* RILEY f : Observations on the Ecology of Water Stridors Zoology M. S. 1912 MS/TV. <>V THE UNIVERSITY OF ILLINOIS LIBRARY ^5 OBSERVATIONS ON THE ECOLOGY OF WATER STRIDERS BY CHARLES FREDERICK CURTIS RILEY A. B. Doane College, 1901 A. B. University of Michigan, 1905 THESIS Submitted in Partial Fulfillment of the Requirements for the Degree of MASTER OF SCIENCE IN ZOOLOGY IN THE GRADUATE SCHOOL OF THE UNIVERSITY OF ILLINOIS 1912 TH5 \vi_ r-4S UNIVERSITY OF ILLINOIS THE GRADUATE SCHOOL 19JT2J 1 HEREBY RECOMMEND THAT THE THESIS PREPARED UNDER MY SUPERVISION BY C: 31 C OIL* . ENTITLED IaJoJjjx- ^tX^MlA^ BE ACCEPTED AS FULFILLING THIS PART OF THE REQUIREMENTS FOR THE DEGREE OF In Charge of Major Work Recommendation concurred in: Committee on Final Examination Digitized by the Internet Archive in 2014 http://archive.org/details/observationsonecOOrile Observations on the Ecology of Water Stridors. Table of Contents. I. Introduction. II. Running Water Habitats 1. Ravines. 2. Springs. 5. Small Temporary Streams. a. Tile-drains and Temporary Streams. 4. Permanent Brooks. a. Behavior During Flood Conditions. b. Drought Conditions. c. Behavior During Conditions of Severe Drought. 5. Creeks. a. Dralnage-di tc h. 6. Rivers. a. Ox-bow Ponds. II. Food and Food Relations. I. Nature and Source of Focd. Food During Captivity. Transportation of Food by Water Currents. Time of Feeding. Response to Water Currents and its Relation to Food. Trial Method of Response to Moving Objects and Its Relation to Food. IV. Summary. V. Bibliography. -3- OESERVATIONS ON THE ECOLOGY OF WATER STRIDERS. I. Introduction. The present paper treats of some of the general ecological relations of water striders. The species that were studied are Gerris remigis Say and Gerri s marginatus Say. The observations recorded are not only with reference to the water striders themselves, but also with reference to the physical conditions of the environment to which the animals respond as they exist near Urbana, Muncie, and White Heath, Illinois. The work was done at the University of Illinois. It was suggested by Doctor C. C. Adams, and was under his immediate direction. The writer is indebted to hio for free access to his library, and also for valuable suggestions. Thanks are due to Professor H. B. Ward, Head of the Department of Zoology, for the use of books from his private library. Thanks are also due Mr. C. A. Hart, of the Illinois State Laboratory of Natural History, for identification of various insects, particularly those used as food by the water striders. The writer appreciates the assistance rendered by Professor J. B. Burrill, of the Department of Botany, in identifying certain plants, the fruit of which is used as food by Gerri s remigis . II. Running Water Habitats. In the discussion of aquatic habitats, it is obvious that some definite scheme of grouping is useful. It assists in the comparison of one sort of habitat with that of another, and it also helps to avoid confusion. Therefore In our -4- ccnsideratlon of water strlder habitats we shall speak of the ravine-brook-creek-rl ver series, as these represent stages in the ideal development of the stream environment. The evolution of the environment toward permanent stream conditions will be traced through as many stages as are found In this vicinity. The physical conditions that seem to be necessary for the existence of water striders will be pointed out, and attention will be directed to the earliest appearance of the water striders In the developing stream series. i. Ravines. The ravine Is the earliest stage in the evelopment of the stream environment. Good examples are found near Urbana, Muncie, and White Heath. These ravines are found on both steep and gentle slopes. About 2 km, north east of Urbana are many ravines, in various stages of development on the steep sides of a deep "gravel pit. In this locality the soil is a sandy clay and is easily eroded by the rains; frost and wind are also agents which aid in this degradation to some extent. The ravines in the earlier stages of formation are shallow, being but .60 cm. — I m. deep, and they have cut back from the gravel pit a few meters only. Others, in later stages of development, have eroded channels, in some instances, to a depth of 4 m. or more, and they extend back from the gravel pit for a distance of about 85 m. In the younger ravines the banks are steep, while in the older ones, they tend to have a somewhat more gradual slope. Such ravines owe their existence chiefly to heavy rain storms. During a severe downpour a considerable volume of water rushes down the larger ravines. The slope being so steep, this surface water quickly passes off after the storm s -5- ceases. At such tines the process of erosion is much in evidence, and the ravines are cut back rapidly. These ravines have no connection with permanent water bodies. The water that flows down their channels passes into the gravel pit. In many of them, holes are formed, which are due ta the combined agency of the current and the grinding .process of the coarser debris. In such places pools of water frequently linger for several days after a rain, and make possible temporary habitats for water striders. It has been mentioned that the ravine represents a very early stage of development in a stream habitat. Running water is present during rains only, and is therefore a temporary condition. Pools exist for a short time after the rain is over. The ravines described are not connected with permanent streams, therefore Gerri s remigi , which is a 1 wingless form , cannot reach such. pools. Gerri s marginatus , being a winged form, can readily migrate to such a location. It is possible for it to live there just so long as the conditions - water and food - remain favorable. From evidence that will be di scusseA later, the writer believes that Gerri s marginatus would be found occasionally In the temporary pools of the larger ravines, if it were not for the meager food supply. The sandy clay banks of the gravel pit are bare of vegetation, and there is little insect life that would be likely to form floating food for water striders. G. marginatus is found in considerable 1. The writer has found two winged specimens during a year of collecting. J numbers not more than 300 . distant from To ; ravel pit, and C. rer.tir;is la also occasi nally taken. However, neither species have been observed in any o£ these ravines connected with the Gravel pit, al nourh those pools have been examined after rains. About 1,5 kin. north east of Muncie, there are high clay bluffs on the north hank of Stony Creel:. The general physio- graphic conditions closel y resemble those described at the rr.wol pit near Urban a. '"ore are also seen -he initial stares or s '.ream development. There are ravines Which have "been cut by the erosion of rains, much in the same '/ay as in the -ravel bank already described. .Tome of these have reached a depth of l.t m. , with a total length a proximately of 50 m. The bluffs are perhaps 17 m. or more in height and very steep. ' he jater from the ravines flons dl c ' V~ into Stony Creel:. The eastern portion of the bluffs is deltoid of veeeta- tion, "out at the top, avid extending back from the creek is an abundance of crass and co: lion neado • plants^ In this verctalional zone erosion is not taking place so rapidly. The ravines arc not of sufficient depth to form, anything more than tTe smallest and most temporary pools. Farther vast the bluffs are hi -her, but not so steep, reccdi ;-..<; from the creel: more yradually. "ere the ravines arc of somewhat greater length, and small temporary pools are some times formed. There is considerable vegetation on the Tr.cc of this slope, cordis tine of forest trees, bushes, and herbaceous plants. In both situations v;here vegetation is found there is con si d oral le insect life. Tone of the ravines have really processed far enough in stares of stream development to form suitable ra' er strider -7- habitats, although on one occasion a stray Gerri s marginatum was found about 6 m. from the edge of the creek on the less steep slope farther to the west, in one of the larger ravine pools. These pools in the ravines are too small and of too temporary a character, and the streams are too swift, existing during rains only. However, there is a plentiful food supply, and this would be in favor of the water striders; but with the one exception, the writer has not observed water striders in any of these situations. wever, it is not difficult to predict, with a considerable degree of accuracy, the changes that will result from the continued process of erosion. These ravines will have so far developed toward the permanent stream stage that their channels will be much deeper and broader. They will retain more of the surface water and for a longer period of time, as their courses will be less steep. In the course of years they will have cut deep enough to receive ground water through seepage. Such a stage of development will tend to make these ravines more favorable habitats for water striders, as there will be a larger amount of water present, and it will be more permanent. There are several small streams, of more or less permanence, emptying into Stcny Creek, in this immediate vicinity, which have already passed through such stages as have been described.