Bulletin No. 99 July

UNIVERSITY OF WYOMING Agricultural Experiment Station

LARAMIE, WYOMING.

BULLETIN NO. 99 JULY. 1913

UBRARY O"TH~ UIJV£RSITY Of WYOMIN8 LARAMIE

The Life-History ot the Sheep-Tick Melophagus ovinus

LEROY D. SWINGLE. Par.. ito!ogiot

Bulletins will be sent free upon request. Address Director Experi- ment Station, Laramie, Wyoming. UNIVERSITY OF WYOMING Agricultural Experiment Station

LARAMIE.

BOARD OF TRUSTEES. Officers. TIMOTHY F. BURKE, 1,1,. B President ARTHUR C. JONES Treasurer FRANK SUMNER BURRAGE, B. A Secretary

Executive Committee. A. B. HAMILTON T·. F. BURKE W. S. INGHAM

Members. Term Appointed Expires 1908 HON. GIBSON CLARK 1915 1911 HON. W. S. INGHAM, B. A 1915 1913 HON. C. D. SPALDING 1915. 1911 HON. ALEXANDER B. HAMILTON, M. D 1917 1911 HON. LYMAN H. BROOKS 1917 1913 I-ION. CHARLES S. BEACI I. ... .1917 1895 HON. TIMOTHY F. BURKE, LL. B 1919 1913 HON. MARY B. DAVID 1919 HON. ROSE A. BIRD MALEY, State Superintendent of Public Instruction Ex officio PRESIDENT C. A. DUNIWAY, Ph. D Ex officio

STATION COUNCIL. C. A. DUNIWA Y, Ph. D , .. President HENRY G. KNIGHT, A. M Director and Agricultural Chemist A. NELSON, Ph. D Botanist and Horticulturist F. E. HEPNER, M. S Assistant Chemist J. A. HILL, B. S '" Wool Specialist O. L. PRIEN, M. D. V Veterinarian A. D. FAVILLE, B. S. , Animal Husbandman J. C. FITTERER, M. S., C. E , Irrigation Engineer S. K. Loy, Ph. D , Chemist T. S. PARSONS, M. S Agronomist L. D. SWINGLE, Ph. D Parasitologist KARL STEIK, M. A , Engineering Chemist JAMES McLAY Stock Superintendent C. D. MOIR , : Clerk F. S. BURRAGE, B. A ' , Secretary The Life-History of the Sheep-Tick Melophagus ouinu»

BY LEROY D. SWINGLE.

INTRODUCTION. This investigation of the life-history of the sheep-tick was made not only because of its scientific importance but also for :l basis upon which to determine effective methods for the utter eradication of the tick. It was the hope of the writer to publish at this time a complete paper on the life-history and eradication of this obnoxious associate of sheep, but owing to failure in . securing a large number of sheep for dipping experiments, it was decided to publish at this time only the results obtained i-i the investigation of the life-history, leaving for a later bulletin the eradication of the tick, which, however, has been worked out except for the practical dipping tests just mentioned. Let it he kept in mind that the life-history has been studied not so much from the purely scientific point of view, as from the standpoint of the eradication of the tick. The sheep-tick, a common and familiar pest, while known 10 biologi ts for many years, has not, so far as I am aware, re- ceived the attention that has been given to many other insects no more common and no more harmful. On this account practical and unfailing methods of eradication have not been prac- ticed in this country. To be sure, many or perhaps most of the sheep-raisers dip their sheep yearly to destroy the tick, yet by the middle of the winter hundreds of these lance-armed pests are to be found living upon a single sheep. The reason is that the dipping was merely of temporary benefit, the life-history of the tick not being sufficiently known to constitute a basis for in- telligent dipping. 4 Wyo. Aqricultural Experiment Station. BUL. 99

The sheep-tick, contrary to general opinion, is not a true tick, such for example as the cattle-tick. Its whole life is spent on the sheep and therefore its life-history is less complex than of the true tick. The sheep-tick is more like a fly than a true tick. It possesses, as do flies, six legs; the true tick has eight. Zoologists regard it as a kind of fly that has lost its wings; it needs no wings, being parasitic during its whole life upon animals that come in close contact with each other. Some authors claim that in addition to its bloodsucking habit, it eats the yolk matter in the wool. I have never seen' any signs of such a habit and am inclined to doubt that such is the case. However, a careful examination of the stomach contents. might show that such material is ingested. It is certain that the flagellates contained in their stomachs are generally obtained by eating the excrement from other ticks which are infected, and so it may be possible that the yolk matter is also sometimes eaten.

LIFE-HISTORY. It is convenient for our purposes to divide the life-history into three stages, namely, the pupa, the young tick sexually immature, and the adult capable of reproduction . Yet this is a more or less artificial division. In the case of most insects, such for example as the house fly, there are four natural divi- sions, namely, the egg, the larva which hatches from the egg, the pupa, and the imago, or adult fly. In the sheep-tick there are present these natural stages, but they are not all apparent except when carefully studied by means of the microscope. The reason lies in the fact that the egg is not laid as in the case of the house fly, but is retained in a uterus where it undergoes development after fertilization, and forms a larva, this larva being nourished in the uterus by a kind of milk secreted by .glands which open into the uterus in the region of the larva's mouth. According to my own observations, the period required for the development of the larva is generally not over a week. When the larva has become so large as to greatly distend the The Life-History of the Sheep-Tick. 5 abdomen, it is born. According to Pratt (1889), the puparium" is completed about twelve hours after the larva is born, and it is not proper to say that the tick gives birth to a pupa. After a variable period of development, the pupa hatches into a young tick, which soon becomes capable of reproduction. These then are the natural stages in the life-history, but for convenience I shall use the term pupa to designate the offspring from the time of birth till it hatches into the young tick pos- sessing the external characters of the sexually mature, or adult tick. In external appearance the larva, as soon as it is born, is the same as the true pupa. The pupa when laid is covered with a white chitinous membrane which soon turns dark brown and hard and is then known as the puparium. Along with the pupa is deposited a gelatinous substance which serves to glue the pupa to the wool. This glue is readily soluble in water yet when dry constitutes a firm cement.

FIG. 1. Enlarged drawing of pupa. a. Lid which ope n s , allowing young tick to escape. FIG. 2. Enlarged drawing of adult female sheep- tick. The two stages, pupa and adult tick, are represented in the figures 1 and 2 respectively. The natural sizes are approxi- mately represented by the lines at one side. The pupae can readily be found by anyone who will examine ticky sheep by separating the wool along the neck, shoulders, belly and thighs,

·Pratt and otbers quoted In this paper use the term puparlum to denote the pupal stage. Packard (1898) uses tbe term in a narrower sense, desig- nating merely the old larval hardened skiilwhlch surrounds the aott pupa within. 6 WyQ -, Aqricultural Experiment Station. BUL. 99

They are rarely found high up near the back region of the sheep. The main objects of this investigation of the life history were: To determine the incubation period of the pupa, i. e., the time elapsing between the laying and the hatching of the pupa; To determine the time required by the young tick to reach sexual maturity, i, e., the time elapsing between its hatching and the laying of its fir t pupa; To determine the length of life of the female tick; To det~rmine the number of pupae laid in a life time, and the rapidity with which they are laid.* The methods used to determine the incubation period of the pupa were such as to place the pupae under quite normal conditions. As far as I have been able to discover from the literature available, the incubation period is known only for pupae kept in boxes in the laboratory. In the fir t method to be tried several females containing large larvae were collected. The larvae are readily recognized as large white bodies distending the abdomen. These ticks were placed in cups on the sheep made in the following manner. A ring was sheared in the wool close to the skin, the wool in the center of the ring being left. Then a muslin band was pasted by means of Le Page's glue perpendicular to the skin and against the outer wall of the furrow made by shearing the wool. A vertical section through the area is shown in figure .t.

FIG. 3. Vertical sectlon showing breeding cup. a. Wool. b. Skin of sbeep. c. Oloth cover. d. OJoth band pasted to the wool. To the top of this band a cheese cloth or muslin cover was sewed, the ticks having been placed within the cup thus formed.

'The egg and intra-uterine tages of the tick have been accurately worked out by Pratt (1893 and 1899). The Life-History of the Sheep-Tick. 7

Before placing the ticks within the cup, the wool was carefully inspected and rid of all pupae which might have been already deposited. Within a day or two, a the case might have been, the cup was opened and the ticks removed. The pupae which they had laid were counted and left in the cup. The cover was sewed on to prevent other ticks from entering the cup. After a few days had elapsed, the cup was opened every day and inspected to determine whether the pupae were hatching. A trial experiment was conducted as follows. On June 30th several pregnant females were placed in such a cup. July rst four pupae were found deposited. In the afternoon several more pregnant females were placed in the cup. On the morning of July 3rd, upon examination sixteen more pupae were found deposited. All the ticks were then removed and the pupae left to hatch. July 19th none had hatched. July arst one was seen to hatch. July zznd four more had hatched. July zath eight more had hatched, July 25 four more, and July 26th one more. August roth there were still two that had not hatched. These were opened and found to be dead. Since the pupae were laid at different times during the period of three days, it is impossible to determine to the day the incubation period. Yet inasmuch as four pupae were laid during the night of June 30th, it is probable that at least one of the first four to hatch was one of these, and also it is fair to assume that the last one to hatch was one of tho e laid during the night of July znd. Therefore, the incubation period must have been from 20 to 23 days. In another experiment ix pupae, which were laid Jl1lY zand, were placed in a cup on the sheep. August roth one hatched. No more had hatched Aug. roth and only 3 were found. The e were opened and found to be immature and dead. The' ncubation period for the one that hatched was 19' days. August r r th five more pupae were placed in the same cup. August 28th one was opened and found to be dried up. One hatched Sept. znd : on Sept. 5th the other three were opened. 8 Wyo. Agricultural Experiment Station. BUL. 99

Two were found to be very immature, while the other was completely developed, but showed no signs of life. For the one that hatched, the incubation period was 22 days. August 13th seven fresh pupae were placed in the cup. None had hatched Sept. znd, On Sept. 4th six had hatched. The other was opened and found to be undeveloped. Thus the incubation period was from 20 to 22 days. Three more pupae were placed in the cup Aug. 23rd. Two hatched Sept. rath. The third hatched Sept. 13th. The incubation period was 20 to 21 days. August 24th two more pupae were placed in the cup. One hatched Sept. rath and the other Sept. 13th. The incubation period was 19 to 20 days. Between Nov. rrth and 13th, thirteen pupae were laid. They were placed in a small cheese cloth sack which was in turn placed in the wool which I drew together well over the sack. The pupae commenced to hatch Dec. 4th. On the 6th they were placed farther from the skin. During the night of Dec. roth the last one hatched. Thus the incubation period was from 22 to 28 days. Coming to the conclusion that the experiments could be. carried on as well without the cups, and knowing that the pupae were not under absolutely natural conditions owing to the cloth over them, I decided to do away with the cups. I marked off a definite area on the side of a sheep by shearing a narrow ring of wool, leaving a tuft in the center six or more inches in diameter. This tuft of wool was carefully freed from any pupae it might contain. Females containing large larvae were then placed in the tuft. The next day all the ticks within and around the tuft of wool were removed from the sheep. Dec. 7th an experiment under such conditions was begun. The following day sixteen pupae were found deposited. The ticks were then removed and for several days thereafter the area was examined to prevent any stray ticks from laying pupae amongst those, the age of which was known. At noon The Life-History of the Sheep-Tick. 9

Dec. 7th one hatched. It was 7-16 of an inch from the skin and 2,% inches from the outer surface of the wool. The pupae farther from the skin were not hatching. The incubation period for this one was between 19 and 20 days. January rst another hatched. It was ~ of an inch from the skin. January 4th two more hatched, one being ~ of an inch from the skin, and the other yS. January 6th four others hatched. They were ~ to 18 of an inch from the skin. January 8th two hatched, one being 18 of an inch from the skin and the other ~ of an inch, with the wool sheared away from one side so that it was somewhat exposed to the weather. The incubation period was from 20 to 36 days. Five pupae were laid in another tuft of wool Feb. roth- arst. March 13th two of them hatched, each being ~ of an inch from the skin and 2~ inches from the surface of the wool. The incubation period was 21 days. March 15th one hatched 18 of an inch from the skin, the incubation period being 23 days. On March rSth the last one hatched. It was one inch from the skin and more or less exposed on one side where the wool was clipped. Incubation period was 26 days. During the night of March rst, seven pupae were laid in another tuft of wool. March 25th one pupa ~ of an inch from the skin and 2 inches from the surface of the wool hatched, making the incubation period 23 days. On March 26th two pupae hatched, ~ of an inch from the skin, making the incubation period 24 days. On March 28th, two more pupae about 1 inch from the skin hatched. The incubation period was 26 days. The other pupae were lost. On April 13th, at 5 P. M., female ticks containing large larvae were placed in another tuft of wool. At 2 P. M., April 15th, they were removed from the sheep, seventeen pupae having been deposited in the tuft of wool. May 3rd-1 pupa about ,% inch from the skin hatched. May 4th-5 pupae about ~ inch from the skin hatched. May 5th-1 pupa about ,% inch from the skin hatched. May 5th;-3 pupae about ~ inch from the skin hatched. 10 Wyo. Agricultural Experiment Station. BUL. 99

May 6th-3 pupae about ?1i inch from the skin hatched. May 7th-1 pupa about 13-16 inch from the skin hatched. May 7th-1 pupa about 15-16 inch from the skin hatched. May 7th-1 pupa about Iy,i inch from the skin hatched. May 9th-1 pupa about 17-16 inch from the skin hatched. The incubation period was from 19 to 25 days. Here again it will be seen that in general the pupae farthest from the warm skin developed slowest. From the foregoing experiments it is apparent that the incubation period is quite variable even under natural conditions. The cause for these variations lies in the temperature under which pupae develop. Under natural conditions it will be noted that the incubation period during the warm summer weather was shorter on the average than during the winter months. In the summer months, from June 30th to Sept. rjth, it varied from 19 to 23 days; between Nov. r rth and Dec. loth, from 22 to 28 days; December 7th to Jan. 13th, from 20 to 36 days, etc. The correlation between the incubation period and the temperature may be shown by giving the average maximum and minimum temperatures for the various months. For July the average maximum temperature was 74 do- gree , and the average minimum temperature was 44 degrees. For August the corresponding averages were 76.S degrees awl 45.6 degrees. During the first 13 days of September, they were 75 degrees and 42.2 degrees. Thus during the warm months, when the average maximum temperature was 76.6 degrees and the minimum 43.9 degrees, the incubation period was from 19 to 23 days. The average maximum temperature from Nov. r r th to Dec. loth was 38-4 degrees, while the minimum was 23.3 degrees. During this period the incubation period varied from 22 to 28 days. From Dec. 7th to Jan. 13th, the average maximum temperature was 27.3 degrees, and the average minimum temperature 7.2 degrees. The incubation period was from 20 to j6 days. The Life-History of the Sheep-Tick. II

The average maximum temperature from Feb. 19th to Mar. rSth, was 38.6 degrees, the minimum 17.3 degrees. The incubation period was from 21 to 26 days. From March rst to March 28th, the incubation period was 23 to 26 days, while the average maximum temperature was 464 degrees and the average minimum temperature was 27.6 degrees. From April 13th to May 9th, the average maximum temperature was S6 degrees and the average minimum 28.2 degrees. The incubation period varied from 19 to 2S days. From these experiments we may make this generalization. The average incubation period was shortest when the average temperature was highest, and vice versa. However, a few degrees difference in temperature had no appreciable effect. This was doubtless due to the fact that the constant warm temperature of the sheep's skin prevented a slight fall of the air temperature from lowering to any appreciable degree the temperature of the pupae located in the wool close to the skin. At this high altitude the maximum and minimum temperatures during the summer months average much lower than in most of the states, such for example as Nebraska, where the temperature is, generally above 8S degrees in the daytime and at night often uncomfortably warm. Therefore in such, states it is probable that during the summer the period of incubation is somewhat shorter. An attempt was made to obtain a shorter incubation period than 19 days, by keeping the pupae in an incubator at a temperature of 37° to 38° Cent. Four pupae, laid April rath, were placed on the same day in the incubator. One hatched in 21 days and another in 22 days. The other two did not develop. April 13th a group of eight pupae were put into the incubator. Two hatched in 20 days and five in 21 days. The other did not hatch. In other trials with the temperature up to 40° C. the pupae were killed. These experiments indicate that the incubation period will 12 Wyo. Agricultural Experiment Station. BUL. 99 not be much less than 19 days even in the warmest weather. One author has stated that the period is from three to 20 days. This can hardly be true. If. the pupae were laid close against the skin of the sheep in the winter, it is probable that there would not be a great difference between the incubation period in winter and in summer. But since they are laid generally from 0 inch to 1;4 inches from the skin, it is certain that the temperature of the pupae in the winter, especially if the sheep are out of doors where the' cold winds may blow into the wool, is much lower one inch from the skin than it is in the summer the same distance from the skin. Then, too, in winter the temperature must be lower 1 inch from the skin than it is 0 of an inch away. And so in the winter the incubation period must necessarily average longer than in summer and must also in a general way depend upon the distance the pupae are from the skin. It has already been shown that in winter there is a general correlation between the length of the incubation period and the distance of the pupae from the skin-the farther the pupae from the skin, the longer the incubation period. The effect of temperature upon the incubation period may be further shown by experiments carried on at laboratory temperatures. When pupae were collected. and kept in boxes at room temperature the number of ticks hatching out in 24 hours was much less than when the boxes were placed above a hot water tank where the temperature ·was much higher. The warmer temperature hastened the incubation. In another experiment pupae which were laid between June aand and June 27th were put into boxes and kept in the north room of a stone laboratory. I have no record of the temperature, but know that the air was chilly, except perhaps for a few hours in the middle of the day. In this case the low temperature inhibited incubation to such an extent that no development whatever took place. Pupae kept in the laboratory where the temperature was from 65 degrees to 80 degrees underwent development, but at The Life-History of the Sheep-Tick. 13 a much lower rate than on the sheep. For example, they did not hatch in less than 39 to 46 days.

DEVELOPMENT OF THE YOUNG TICK TO SEXUAL MATURITY. From the standpoint of eradication of the tick, the time required for young ticks to reach the capacity to lay pupae is very important, since it is difficult to find a dip that will kill all of the pupae. Here, as in the case of the pupae, it was necessary to carryon the experiments under natural conditions. One cannot conceive that young ticks put on a sheep each day to suck, and then removed to boxes, would have a natural development. Therefore the experiments were carried on with ticks kept continually on sheep. Much labor and time were spent in trying to confine the young ticks in cups similar to those previously described. For the experiments to be absolutely without a shadow of error, it was necessary to know beyond doubt that the ticks laying pupae were those that hatched on a certain known date. It was thought that the ticks could be so controlled in these cups as to remove any liability of confusion respecting their identity. It might be said in the beginning that practically all the experiments conducted in this manner were failures. Yet from a scientific standpoint it is worth while to record some of them in detail. In order to have a large number of young ticks hatched out on the same day it was necessary to collect large quantities of pupae.* ' On June 23rd eight young ticks, which hatched June aand-ajrd were placed in a cup. These all died. June 29th- 30th, twenty-two young ticks hatched. They were placed' ill a cup. Three of them died; seven of them were found doing well July 3rd. None could be found July 8th. They probably escaped underneath the edge of the cup. June 26th, fifteen young ticks, hatched June 25th-26th, were put into a cup on another sheep. June 28th, eighteen

.The work was handicapped owing to the difficulty In securing materIal In sufficient quantities. Wyo. Agricultural E~periment Station. BUL. 99 young ticks, hatched June 26th-27th, were placed in a cup on the other side of the same sheep. July 8th there were only four in the first cup. On this date all were placed together in one cup, making 3 males and 3 females. July rSth one female, containing a large larva was found dead. There was present another female with a large larva. This was laid the following day. Therefore in this case the period from the hatching of the ticks till the laying of their first pupae, was between 20 and 23 days. On July 4th thirty young ticks, which hatched July and- 4th, were placed in another cup. On the 8th seventeen live ones were present. One of them was a female. July i Sth only four could be found, the others having made their escape. They all perished later. July 6th another group of young ticks, hatched July 5th- 6th, were placed in a cup on another sheep. July 8th they had all perished. July 8th thirty-two young ticks, which hatched July 7th- 8th, were placed in a cup. These all died. July roth thirty young ticks, hatched July 9th-lqth, were placed in another cup. All but one were dead July r ath. On this day 23 more were added, which had hatched July r rth-rath. These all perished. Into a cup on another sheep, were placed 17 young ticks, which hatched July z.tst-aand, July 24th all were dead. On this day 20 other ticks, hatched July 23rd-24th, were put into a cup. July zoth they were all dead. July 24th twenty others which had hatched the-day preceding, were put into another cup. July zoth nine were living. On the 27th only 3 could be found and on August znd all were dead. It is perhaps needless to record in detail the rest of the experiments by means of the cup method. Nine more experiments using 201 ticks were made. The ticks either died or escaped from the cups, so that no results were obtained. In some of these experiments the pupae were put into the cups so that they might hatch under natural conditions. But the results were no better. Then an experiment was tried in The Life-History of the Sheep-Tick. which the cup was covered with a wire gauze, thinking that possibly the muslin cover did not admit enough air. This brought no improvement. It was found, however, that they lived much better when placed in large cups, 8 or 10 inches ill, diameter. The difficulty of making the large cup absolutely tick proof for the course of several weeks was too great and so the method was erttirely abandoned. It is hardly possible that the glue which hardened quickly was a factor in the destruction of the ticks. The results were the same whether the cups were placed on the side, shoulders, rump or back of the sheep, or whether lambs or old sheep were used. Nor could the death of the ticks be ascribed to any general condition of the sheep's wool or skin, because the ticks lived and did well outside the cups. Therefore since they lived better in the large cups than in the small ones, one is tempted to believe their death was due chiefly to confinement, though even this would seem absurd. And yet many other insects and higher animals will not endure confinement, even though the conditions are natural except for this one factor. On August z t st thirty-nine young ticks, hatched August roth-arst, were allowed to go free on a lamb from which all ticks had been remove 1. On Sept. r r th two females with large larvae were found. September rzth four more females, containing large larvae were found. On the r jth one pupa was deposited. On the rath four more were found. On the 15th another, anti on the roth still another. This makes 9 pupae which were laid, and 9' females and 3 males were found on the lamb at the time. The period required for these ticks to reach the ability to lay their first pupae was therefore 24-30 days. The further life of these ticks will be described under a discussion of the length of life of the tick. Although this method was successful it seemed wise to devise some method which would insure absolute certainty regarding the identity of the ticks. Various methods of marking ticks were now tried. In the first place I attempted by means of glue to stick on to the 16 Wyo. Agricultural Experiment Station. BUL. 99 dorsal side of their abdomens a very tiny piece of paper bear- ing a number. But it was impossible to make the glue hold for more than a few hours. I then tried to mark them by coloring the glue and putting a small drop on their abdomens. This failed to stick permanently. Then in the place of glue, colored celloidin was tried, but this was no better. I then attempted to stain the abdomen with comparitively non-poison- ous stains, but the chitinous covering of the ticks would not take the stain sufficiently. Finally as a last resort, it was found possible to mark them by tying colored silk thread about the constricted por- tion joining the abdomen and thorax. This method was practical, though slightly tedious. Fine silk thread of various colors was secured, and split into its three component strands. These strands were very fine, yet sufficiently strong. By carefully holding the thorax and legs of the tick between the thumb and second finger, leaving the abdomen slightly free, it was possible to tie the thread between the abdomen and thorax by using forceps. The ends of the legs are each armed, as shown in the figure, with two large claws which hook viciously into the silk and prevent tying it unless their movements are prevented. These threads remained on the ticks for months, and. served perfectly as a means for identifying them. On December znd a lamb was freed from ticks. Then 36 young ticks, hatched December r st-and, were placed on it. De- cember 6th 29 of them were found doing well. Some were copulating. On December rath I collected 10 females and tied red silk threads on them. While doing so, one was killed. De- cember 13th three more females and 18 males were found and marked with red silk. December 14th I was able to find 12 of the females, ten of which contained plainly visible larvae. On December roth one pupa was laid. December 17th four pupae were deposited. On the r Sth five more pupae were laid. De- cember 19th another pupa was found and on the 23rd still another. Thus the time required to reach sexual maturity was 1-1- to 21 days. The further history of these ticks will be related in the discussion on the length of life of the tick. The Life-History of the Sheep-Tick.

Twenty-one ticks, hatched January 24th-26th, were placed on a Iamb January 26th. I recovered 14 of them right after they had sucked blood, and immediately tied blue silk thread on them. January 30th the 14 labeled ticks were found. February 7th one of them died. On the r rth two pupae were laid by them. The least time required by these to reach sexual maturity was from 17 to 18 days. In the foregoing experiments the threads were not tied on the young ticks before putting them on the sheep, for the reason that the ticks are small and slender before they have sucked blood and it therefore appeared impossible to tie the strings on them tight enough to stay without injuring or preventing them from sucking blood. Also it really seemed unnecessary, because one who has seen a great number of ticks can distinguish one a few days old from an old one. But to eliminate all possibility of error, an experiment was made in which the ticks were marked with silk thread before being placed on the sheep. Seventeen ticks hatched out March roth-aoth. On the latter date they were labeled with brown silk threads and placed on a Iamb which had been freed from ticks. On the following day eight ticks, hatched March zoth-arst, and marked with black silk, were placed on the opposite side of the same Iamb. March 30th fifteen of the ticks were found and one of the brown group contained a larva. April' 4th a pupa was laid by the brown group. Also two others of the brown group and one of the black contained large embryos. April 5th the brown ones laid two pupae and on the next day the black one laid its pupa. On April 8th one pupa and on April 12th two pupae were laid by the brown group. The others did not lay pupae until it was time for the first ones to lay again, and so these were not followed further. The time required to reach sexual maturity was, therefore, from 15 to 23 days. In these cases all possibility of error was removed. From the results of these experiments it may Le stated that the time required for the young female tick to reach sexual maturity is between 14 and 30 days. By using thou- ]8 Wyo. Aqricultural Experiment Station. BUL. 09 sands of ticks in the experiments it might be possible to make the period less than ]4 days, yet in nature it is not likely to be much less than this, for the ticks used in the experiments were kept close together so that copulation was possible as soon as the ticks were sufficiently developed; whereas in nature after all the ticks have been killed by dipping, only a tick here awl there is hatching out, and the chances for an early copulation are very light. As for the possibility of the time being longer than 30 days, of course this limit is not at all fixed. It varies with conditions. If a female does not copulate for two months or more, it is evident that she will not lay pupae in less than two months. The temperature has not much effect upon the period. And why should it have, at least under natural conditions? Ticks, unlike pupae, have locomotion and when the temperature is high, they come out on the surface of the wool, and when it is low they cling tightly against the warm skin. On hot summer days one may see fifty ticks crawling over the SU!"- face of the wool, while on cold days not one is in evidence. Therefore there is little variation in their temperature.

THE LENGTH OF LIFE OF A FEMALE TICK AND THE NUMBER OF PUPAE LAID. To determine the length of life of the tick the cup metho 1 was tried first. It was my intention to follow the groups of ticks placed therein until they died, but since all of them die i or escaped from the cups within two or three weeks the method was abandoned. The only method that proved successful was that of marking the young ticks with silk thread and turning them loose on the sheep. They were placed, therefore, under perfectly natural conditions, for the strings were cut 0 short as not to entangle the legs nor catch in the wool. ~ or were they tied so tightly as to constrict the body of the tick. The ticks from the first experiment, which was made to determine the time required to reach sexual maturity, were marked September zoth with red silk threads. These ticks, it will be remembered, hatched between August roth and 21St. The Life-History of the Sheep-Tick .

. There were three males arid nine female in the group. Septem- ber zznd one of the males became swollen, turned black and died. On the 25th one of the females did the same and died the following day. After the 25th only seven females could be found, one evidently having escaped. On November 7th only six females were to be found. I do not know whether the one had died or escaped from the sheep. November 25th one female died. December 9th the abdomen of one of the females became greatly distended with the transparent coelomic fluid, and December rath it was dead. Only four of the nine were left. December 15th another female was missing, but I do not know whether it died or escaped. December 29th one of the three remaining females died. January 4th another was dead and on the 17th the last one died. Of the females, the deaths 'of which were certain, one died at the age of 36 days, another at 97, another at 114, another at 131, .another at 137, and the last at the age of 150 days, or 5 months. A careful daily record of the pupae laid by this group of ticks during their life-time having been kept, the following results may be presented. The ticks that lived at least 36 days produced on the average 2 pupae each; those that lived 97 days, 7.42 pupae each; those that lived 114 days, 9.°48 pupae; those that lived 131 days, 11.45 pupae; those living 137 days, 13-46; and the one living 150 days, 14.72 pupae. Counting from the time the ticks began to lay pupae we find that the average time required for a tick to develop and lay a pupa was 7.89 days. In another experiment the twelve females which hatched December rst-znd were followed till all were dead. These were marked with red silk threads. On December 16th the fir-st pupa was laid, while ten of the group contained large embryos. On December 17th four more pupae were laid. On the r Sth five more were laid. And so it may be counted that on the average this group laid their first pupae at the age of 17 day>, December 30th one tick died. January znd three more died. On the zand another died. February loth another died. March

• 20 Wyo. Agricultural Experiment Station. BUL. Y9

26th one of the number was missing. March zoth one of the females turned deep red in color and on the 30th died. April 8th another female was missing; I believe it escaped from the sheep. April rath a female laid a pupa and died immediately. One of the two remaining ticks was lost on May r r th. The other laid a pupa on the r jth and was lost on the 15th. Count- ing only. those the deaths of which were certain one died in 28 days, three in 31 days, one in 51 days, one in 70 days, one in 119 days, and the last in 132 days. The last two of the group lived at least 161 days and 165 days respectively. On the average the number of pupae laid by the ticks living 28 days was 2; by those living 31 days the number was 2.54; by those living 51 days, 4.8; by those living 70 days, 6.8; by those living 119 days, 13.26; by those living 132 days, 14.6; by those living 161 days, 15.6; and by the one living 165 days, 16.6. In the case of the last two ticks the rate of pupa laying was much de- creased during the last month of their known existence. From April 13th to May 13th both together laid only 3 pupae. This decrease in rapidity of laying pupae is not due to the warmer weather for it was no warmer than in September and October when the other group was laying at the rate of I pupae in 7.89 days. The falling off is probably due to senility. The average rate of pupa laying, counting from the time they began to lay up to May 13th when the last pupa was laid, was I pupa every 7.99 days for each tick. This it will be noted is practically the same as the time required by the preceding group of ticks, there being only 2 hours difference. Thus, ticks living for 4 months, as is probably the case with most of them in nature, will lay in their lifetime from 10 to 12 pupae. But some of the ticks will live at least six months and their brood will number from 15 to 20. These results are quite different from those commonly given in articles on the sheep tick. In an article occurring in the Journal of the Department of Agriculture and Technical Instruction, Ireland, 1906, it is stated that "the same female is able to produce five or more young successively." Hopkins The Life-History of the Sheep-Tick. 21

(1890) says that according to Packard (Common Insects p. 85) "Each female produces but two or three young." Cooper Curtice (18g0) writes: "Some authorities say that each female produces but one or two of these pupa ria ; others say that they can lay about eight or nine during their life-time." Lugger (1896) says "When we consider that a female of this parasite only produces one offspring at a time, and perhaps only four or five during her whole existence it is difficult to explain the very- large number of ticks sometimes found upon a single sheep." Neumann (1907) says "the female only lays one larva at a time, and there are but four or five in the course of a year." Pratt (1899) says, "the young animals are born one at a time and at intervals in the summer-time of several weeks." Davison (1910) writes, "a female lays but one puparium at a time, and only five, or possibly eight during her life time." He further says, "the life time of the female is said by competent authorities to be from three to four months, although it is not denied that it may survive for a period of twelve months." These quotations show that the general opirnon every- where is that the sheep-tick lays very few pupae in a life-time and that several weeks intervene between the laying of suc- cessive individuals. However; since it has been shown that a female may live at least five and one-half months laying a pupa every eight days it is not difficult to see how sheep in the course of a few months may become heavily infested, although but one pupa is deposited at a time. The tick is exposed to very little danger of destruction either in summer or winter, and hence the probability is that most of them live fully six months. The ticks used in the experiments were handled every day and probably died sooner than they would have otherwise. Some one may wonder how it was possible to follow with any degree of success a dozen ticks on a sheep for a period of five or six months. The fact is that it is not as difficult as would be supposed by one who is not acquainted with the habits of the sheep-tick. It was di covered that if a dozen 22 Wyo. Aqriculturol Experiment Station. BUL. 99 female ticks be placed in the wool within a circle having a diameter of 2 inches, the following day they will most generally be found very near that area, at least within a radius of three or four inches. In the experiments the ticks were rounded up each day and placed within a small area. Nevertheless one was lost oc- casionally and could not be found anywhere on the sheep. In such cases it is probable that the tick crawled to the surface of the wool and was rubbed off, or accidently fell from the sheep. The sheep-tick spends its whole life on the sheep. It is a false idea that the tick may drop off the sheep and live for a long time in the grass or brush and be picked up again by sheep sometime later, as is the case with the true tick. Experiments on keeping ticks in boxes covered with gauze show that the sheep-tick's life off the sheep is short. They were all dead in four days whether they were kept warm or cool. Young ticks, before taking a meal, can be kept a little longer and in one case years ago the writer was able to keep a tick alive off the sheep for seven days. A large percentage of them will die within forty-eight hours. For example, 2IO ticks were gathered March rSth. On the roth 38 were dead. March zoth, 48 hours after they were collected, 71 more were dead, or more than half of them. March arst 55 more or them were dead. March 22nd the remaining 46 were dead. March 5th 73 ticks were collected. On the 7th 13 were dead. On the following day 47 more were dead. March 9th no living ticks were present. A sheep free from ticks can be kept for months beside a heavily infected one with a tight partition only three feet high between them without becoming infected. Sheep-ticks have very little instinct for migration, unless they are disturbed by shearing the wool. As already mentioned a bunch of females placed in the wool of a sheep will be found in practically the same place for two days. Males, however, are more inclined to migrate. This may be due to a sexual instinct impelling them to search for females. The Life-History of the Sheep-Tick. 23

SUMMARY OF THE LIFE-CYCLE.

I. The egg is fertilized and develops through the embryo- mic and most of the larval stage within the body of the female tick. It is laid as a larva which changes into the pupa stage about 12 hours later. (For convenience the term pupa is used in this paper to designate the offspring from the time it was born until it was hatched.) 2. Pupae require during the summer months from 19 to 23 days to hatch. In the winter-and at Laramie one can include the time from November rst to May r st-s-from 19 to 36 days are required in case the sheep are kept in the barn. Were they turned out doors in the cold wind, the probability is that in some cases the period might increase to 40 or 4S days. The period of incubation is greatly affected by the temperature, and therefore by the distance the pupae are laid from the skin of the sheep, especially in the winter. 3. The time required for females to reach sexual maturity is variable. Generally it will be from 14 to 30 days. But it is al 0 true that certain factors might make the time much longer. Males and remales are capable of copulating within three or four days after hatching. 4. The whole life of the tick is spent on' the sheep. They will not live more than a few days off their ho t. S. Female ticks were followed for five and one-half month. Some probably live much longer. Many die earlier. There is a great mortality among the young before they take their first meal. The change from life in a puparium, supplied with food from the mother, to an independent exi tence on the sheep is naturally attended with considerable mortality. 6. The number of pupae laid by a female depends upon the length of her life. For a female living, say four months. the time one might regard as an average life-time, the number is about TO to 12 pupae. For one living six months, the number is I S or more. 7. The rate of pupa laying, counting from the time the first one is laid, is about one pupa every 7 or 8 days. 24 Wyo. Aqricultural Experiment Station. nUL. 99

LITERATURE CITED. Curtice, C. 1890. The Animal Parasites of Sheep. U. S. Dept. of Agric., Bu. An. Industry, Wash., pp. 39-44. Davison, A. G.

1910. The Ked or Sheep Louse. ..<1 Agric. J ourn. of the Cape of Oood.Hope, 36 :398-403·

Hopkins, A. D. Jb e 18g0. Melophagus ouinus. fIlW 'I "I:l( West Virginia Report, p. IS0. 'lr{a . Lugger, O. :l 5f!J 1896· Melophagus ovinus. .Igirrr b Minnesota Bulletin, 48 :169-7Q1£n-g a'

Neumann, L. G. [t -:lITh 1907. A Treatise on the Parasites and Parasitic Diseases of the Domesticated Animals. (Translated by George Fleming). . William R. Jenkins Co., New York. Packard, A. S. 1898. A Text-Book of Entomology. The Macmillan Company, New York. Pratt, H. S. 1893. Beitrage zur Kenntnis der Pupiparen. (Die Larve von Melophagus ovinus). Archiv. f. Naturgesch., Bd. 53.

1899. The Anatomy of the Female Genital Tract of the Pupipara as Observed in Melophagus ovinus. Zeitschr. f. Wiss. Zoo1., 66 :16-42.