Pill Bug Biology A Spider's

Spinach, But a Gary Raham, PO Box 399, Wellington, CO 80549, received his B.S. and M.S. in Biology from the Univ. of Michiganin 1968 and 1969, respectively. After teaching secondary biology and physics at Akron, Coloradofor two years, he entered the field of commercial Biologist's Deligh art. Rahamis a graphicartist and illustratorfor a Fort Collins, Col- orado printing firm. He is a member of the Guild of Natural Science Illustratorsand the Colo-Wyo Academy of Science. His articleon appeared in ABTin 1978 and one on Diatoms in 1979. He also has written a filmstripseries on lichens for Carolina Biological Supply and science articles for various magazines, in- cluding Highlightsfor Children.Raham's first book, Dinosaursin the Garden,A Naturalist'sGuide to BackyardBiology, will be published in Downloaded from http://online.ucpress.edu/abt/article-pdf/48/1/9/41822/4448178.pdf by guest on 01 October 2021 Gary Raham 1986.

Most spiders, it seems, find pill bugs to be a dis- from the air with minimal water loss. Pill bugs, how- tasteful meal-something to be eaten only in emer- ever, are relatively unspecialized for their land life, a gencies. Biologists, however, should find much to fact that is consistent with a recent invasion of the like about them, at least in their adaptations to land land. The earliest fossils of these are life if not their flavor. (Although, I'm told by a rep- found in Baltic amber of upper Eocene or lower Oli- utable biologist, their flavor is not objectionable. gocene age (Edney 1968) and, by that point in time, They're crunchy and a little on the salty side.) they were very similar to modern forms. Their major Most of you may remember pill bugs from child- adaptations to the rigors of terrestriallife have been hood. (Figure 1). You may even have eaten a few. behavioral, which may reflect the usual sequence of Although the casual observer may regard them as events when organisms pioneer new environments. insects, they are crustaceans, representatives of the This isn't to say that pill bugs and their kin are order that have carved out a successful niche without physical tools suited to land life. Edney in a variety of terrestrialhabitats. Pill bugs, in partic- (1968), Cloudsley-Thompson (1968) and other re- ular, have the ability to roll up (Figure 2) into a ball searchers in the field recognize a variety of traits in whereas some of their isopod cousins cannot. I be- marine isopods that preadapted them in many ways lieve their great value to classroom biologists is three- to land life. Isopods possess walking legs ratherthan fold: they are common and easy to find, especially in more specialized, flipper-like appendages. They are grassland and semi-arid locales; they are easy to cul- flattened from top to bottom and hug the ground ture for long periods in the classroom;and they show closely, which efficiently distributes the pull of a variety of physical and behavioral adaptations to gravity. Isopods retain their eggs in a brood chamber, land life that are easily demonstrated in the lab. which, in their land dwelling members, helps keep them from drying out. They also possess internal fer- The Pill Bug Family Tree tilization-another plus for a dry land existence. Mouth parts designed for chewing rather than filter Pill bugs are relative newcomers to terra firma. Ar- feeding also aided their land colonization. Neverthe- achnids probably led the way with a scorpion-like less, water is a crucialfactor in their lives, and shortly creatureforced from the secure, if crowded, Silurian I'll describe how it effects their physiology and be- seas. Insect ancestors weren't too far behind and havior. went ahead to become the most successful land (and air) colonizers of all. The ancient lineages of these a lattergroups are reflected in their intricatespecializa- Making Living tions to land life-specializations for conserving All organisms solve common problems on the road water, for reproduction and for extracting oxygen to survival: acquiring energy either directly from the from an envelope of dessicating gases. Most terres- sun or indirectly by eating; getting oxygen to metab- trialarthropods, for example, have a waxy cuticle for olize that food; taking care of waste products;fending reducing water loss through their exoskeleton; coe- off "enemies" trying to make their living; and finding lomic organs help regulate salt balance in the blood successful ways to reproduce. Land creatures have and specialized respiratory organs extract oxygen the additional problems of preserving the water con-

PILLBUG BIOLOGY 9 Antennule

Ant'enna MRxhpo

''' {'tV ':'S Downloaded from http://online.ucpress.edu/abt/article-pdf/48/1/9/41822/4448178.pdf by guest on 01 October 2021

di \

Figure 1. A generalized terrestrialisopod. They have a body with seven thoracicsegments each carryinga pair of walking legs and six smaller abdominal segments. The number of legs alone helps distinguish them from insects and spiders, which have three and four pair, respectively, and pill millipedes which have eleven to thirteen pair. tent of their bodies and coping with extremes in tem- results in greater water loss than for other terrestrial perature. , but this system of waste removal is also TheWater Problem cheaper in terms of energy expended. Loss of water from respiratory membranes is also Pill bugs lose water in four basic ways: through a serious problem. In an aquatic habitat an organism their skin in general; from evaporation from respi- can be most efficient in extractingoxygen from water ratory membranes; in their feces; and during excre- by maximizing the surface area exposed to aerated tion of nitrogen. Studies have shown that water loss water. In small simple diffusion is sufficient. through their skins is proportionalto the vapor pres- In larger ones, thin, filamentous gills work admirably sure of water in the air. Also, an increase in temper- well. In dry air, however, maximizing surface area ature doesn't result in a sudden increase in perme- also maximizes evaporation and thus water loss. Ter- abilityat some point. Both these facts imply that there restrialinvertebrates have developed several physical is no waterproofing mechanism similar to the waxy strategies for accomplishing this and -the pill bug's coating of insects. Pill bugs may have a lipid layer solution is least efficient. beneath the endocuticle that cuts losses somewhat, but basically they are at the mercy of the ambient RespiratoryStrategies temperature and humidity. First, there's the "pipe-air-to-the-tissues"approach Pill bugs lose some water in their feces although adopted largely by insects (Figure 3). In this system the water content of their solid waste is lower than a network of tubes called tracheae branch and re- that of the food they consume. Nitrogen is excreted branch throughout the body carrying air directly to in the form of ammonia rather than uric acid which the tissues where diffusion can take place. A pair of

10 THE AMERICAN BIOLOGY TEACHER, VOLUME 48, NO. 1, JANUARY 1986 vulgare When Rolled Up a copper-containing molecule. Dallinger, in a 1977 Lateralview Anterior view paper, showed that terrestrial isopods selected food based on the amount of copper reserves in their bodies. Copper enriched isopods preferred low copper litter and copper deficient animals selected a much greater proportion of copper enriched litter. One important question, however, is whether copper cephalothaahitenax eye is truly a limiting factor for land-bound isopods or an element on which they must not get overdosed. Has- Figure 2. Pill bugs roll up when disturbed and in that shape do somewhat resemble a pill. This ability helps to sall and Rushton in a 1982 study felt the latter situ- conserve water loss as well as provide protection from ation might be the case after looking closely at an- predators. other aspect of the pill bug diet: they eat their own feces. openings to the system are usually found on each In fact, a little over nine percent of a pill bug's diet abdominal segment and the openings are surrounded is feces. Growth rates of both copper enriched and by muscles that can close off the system if too much copper deficient animals were slowed when they were prevented from eating their feces. Hassall and

drying occurs. Downloaded from http://online.ucpress.edu/abt/article-pdf/48/1/9/41822/4448178.pdf by guest on 01 October 2021 Secondly, you find the "run-blood-by-a-sack-of- Rushton found copper was not a nutrient limiter. air" technique pioneered by spiders and other ar- Eating feces, or coprophagy, as it is delicately called achnids. In this system air is allowed in a chamber in scientific jargon, seems to accomplish two things: called the atrium and it flows from there into plate- it allows microorganisms to act on the material and like hollows around which blood is forced to flow. further break down hard-to-digest items, and it pro- The air spaces are thin, flat and stacked one upon vides some survival value when food is limited. the other much like the pages of a book and thus The former aspect of coprophagy is important to book lung is an appropriate name for these struc- tures. Like the insects spiders can close off the A. PSEUDOTRACHEAL SYSTEM Air (TerrestrialIsopods) opening to the atrium if conditions are too dry. The pill bug's technique is similar to a book lung in some ways but much less sophisticated. If you flip Pleopod N a pill bug on its back you will find two pair of white, Pseudotracheae bean-shaped structures on the first two abdominal segments (near the rear end of the ). These are C. BOOK LUNG (Spiders) modified areas of appendages called pleopods. The B. TRACHEAL SYSTEM white appearance is from air trapped within hollow (Insects) Air s\ > spaces called pseudotracheae. If you place a drop of Tracheae water on the abdomen you may see a bubble which 5pracle m marks the opening to these air sacks. Even though Air Hemolymph they're called pseudotracheae, pill bug blood or he- (blood) molymph picks up oxygen as it bathes the area rather than having oxygen diffuse directly from the sack to osskeleton tissues as in insect tracheal systems. Oxygen from this source is supplemented by oxygen that diffuses D. GILLS directly through the cuticle. About 10 percent of a pill (Crustaceans & other aquatic arthropods) bug's needs are met by simple diffusion. Because Waterfljow pseudotracheae can't be closed off by muscular ac- tion, up to 42 percent of the animals water loss is through this organ.

Findingthe Groceries Exoskeieton Pill bugs are rather eclectic eaters, consuming a va- riety of fleshy fruits, fungi, dead and decaying Flow matter, spider's eggs, seedlings and even ant drop- Figure 3. Arthropods have adopted several strategies for pings. Their food selection is determined largely by extracting oxygen from the air without drying out in the their water needs and their dependence on a source process. Terrestrial isopods have a workable, though somewhat inefficient, pseudotracheal system that suppli- of copper. ments direct diffusion. (A. Adapted from a drawing in Copper is important to pill bugs because the ox- Kaestner, B. & D. Based on drawings from Clarke and C. ygen carrying chemical in their blood is hemocyanin, redrawn from Foelix)

PILL BUG BIOLOGY 11 pill bugs because their digestive systems are simple A Pill Bug Mimic and probably less efficient at absorbing nutrients than other creatures eating much the same food, such as snails and slugs. A pill bug's system is pretty much a straight tube from mouth to anus with only two pairs of anterior hepatopancreatic glands to help di- gest food juices, whereas snails have "salivary" glands, stomach, crop and various intestinal glands that aid in food digestion. Water relations enter into isopod eating strategies in the form of osmoregulation-in other words the concentration of their blood-the amount of water relative to the amount of dissolved salts. Insects and most other organisms tolerate little shift in the op- timum concentration of salts in the blood but pill bugs and other isopods, including marine forms, are Downloaded from http://online.ucpress.edu/abt/article-pdf/48/1/9/41822/4448178.pdf by guest on 01 October 2021 quite tolerate of fluctuations. Presumably what reg- ulation they impose comes from selecting food of fairly high water content and relying on various be- Lactrodectus mactans Armadillidium klugii havioral techniques for ridding themselves of any (European black-widow) (Pill Bug) water excesses. Ventral view Dorsal view, rolled up Fending Off the Foe If pill bugs could have nightmares a recurring one Figure 5. A of European pill bug has adopted the might involve images of a six-eyed demon with rapier same color markings as the European black widow spider it from predation by jaws attacking suddenly out of the darkness (Figure -a technique that apparently protects lizards. (Drawing by the author. A. klugii based on drawing 4). Dysderid spiders seen at close range are formi- in Levy's paper; L. mactans redrawn from A Guide to Spiders dable looking, with specialized jaws designed to and Their Kin.) pierce pill bug armour. Also, these spiders are not deterred by their prey's acrid secretions, which do tential enemies. The secretions of pill bugs are pro- serve to deter many species of spiders and other po- duced by repugnatorial glands located dorsally in pairs along the margins of their thoracic segments. Although effective, the expense in terms of water loss must be great as the size of these glands decreases in species that are progressively adapted to drier and drier habitats. Herbert W. Levi in 1964 reported another unusual defense used by a European pill bug. It has adopted a strategy of protective coloration by looking nearly identical to the abdomen of the European black widow spider (Figure 5). Presumably this offers pro- tection against certain lizards, who, after sampling a widow and feeling poorly as a result, avoid anything with the same distinctive red and black coloration. Birds, amphibians, mites and centipedes also take their toll on pill bugs although a complete list of pred- ators has probably not been compiled. For many of these predators the "active" defenses of pill bugs are not a great factor. Rather it is the pill bugs' preference for dark, narrow burrows and sheltered areas that keep them hidden from most of their enemies. At least one species of parasite, an acanthoce- phalan worm, has managed to "reprogram" pill bug behavior to its own advantage. Janice Moore at Col- orado State University has followed the life cycle of this enterprising creature whose primary host is the Figure 4. starling. Within the starling the worm reaches sexual

12 THE AMERICAN BIOLOGY TEACHER, VOLUME 48, NO. 1, JANUARY 1986 maturityand lays its eggs within the bird's intestines. The eggs are passed with the feces which are in turn eaten by pill bugs. In this secondary host the young worms hatch and burrow through the gut wall to remain attached to the outside, hanging in the body cavity. There they grow and share the pill bugs dinner, reaching a size of several millimeters. Since pill bugs are about eight millimeters long a substan- tial fraction of their body cavity is occupied by the intruders. Infected female bugs were found to be sterile. The most interesting aspect of the relation- ship, however, is that by some unknown mechanism the presence of the parasite alters the pill bug's normal behavior in such a way that it becomes more susceptible to the bird predators who will serve as the worm's primary host. Infected pill bugs were Downloaded from http://online.ucpress.edu/abt/article-pdf/48/1/9/41822/4448178.pdf by guest on 01 October 2021 found to frequent areas of low humidity with greater frequency and showed no preference for sheltered areas-exactly the opposite behavior of their unin- fected brethren. These tendencies kept them in ex- posed areas where starlings were more likely to find them. Pill bugs become most susceptible to all their ene- mies and the environment during molting periods. Females undergo extra reproductive molts and, not A surprisingly, their mortality is higher. Paris found in Figures 6A and 6B. Photograph 6A shows a female Arma- a 1963 study of California grassland pill bugs that dillidiumvulgare, ventral side up, with a brood pouch full of males outnumbered females after the first breeding eggs. The brood pouch is created by overlapping, platelike season even though the initial sex ratio was 1:1. extensions of the first five pairs of walking legs. Aquatic isopods also possess brood pouches, a situation which may Overall mortality in the,same study was found to be have helped preadapt this group for a terrestrialexistence. high with only 19 percent of pill bugs surviving the (Photographby the author, cross section 6B redrawn from first six months and 1 percent surviving to the ripe Lawrence) old age of four. Cross-section ThroughThorax of Oniscus however,semst bew.liie. Raisinga Family bodycavity Pill bugs inherited from their aquatic relatives one served as a reproductive stratagem which definitely eggs in brood preadaptationto land life: the brood pouch. Females - I~~PL BU BIOLOGYchamber 13 shed their eggs into a chamber formed by plate-like, overlapping extensions of the first five thoracic legs. Withinthis chamberthe young develop over a period oostegite from two to three months, relatively secure from en- vironmentaldangers. Brood size varies from a couple of dozen to several hundred depending on the age of the female. The older and larger the female the B walkinglegs more young she will carry. Paris' Californiapill bugs had two broods per year, breeding from April to Sep- bugs) only contnbutes one kind of sex chromosome tember. The same species, Armadillidiumvulgare, in in those individuals that produce monosexual England usually produces one brood per year and broods. gravid females can be found from May onwards. French researchers have recently found that in Females do need males to produce fertile eggs some populations of Armadillidiumthere are F-factors, (they're not parthenogenic). However, sperm can presumably virus borne or loose scraps of DNA in survive in the female for up to a year. Curiously, the cytoplasm, that can transform genetic males into broods can be mixed with regard to sex of the off- spring or they can be comprised of all males or all females. One possibility is that the sex chromosomes are selectively segregated during meiosis, such that the sex determining partner (female in the case of pill -LITTORAL FOREST GRASSLAND SEMI-ARID ARID Family: Ligiidae Family: Oniscidae Family: Armadillididae Family: Porcellionidae Family: Armadillidae

o2< ~o4 '<< i @@d ifl2 a.

i--J-so L) (n 0 _ aX SaSRock Slaters Sow Bugs Pill Bugs Sow Bugs Pill Bugs Can they roll up? No No Yes, excluding No Yes, including (Conglobate) antennae antennae Downloaded from http://online.ucpress.edu/abt/article-pdf/48/1/9/41822/4448178.pdf by guest on 01 October 2021 Negative, except Positive, except at Negative, except at Reactiontoemightrat high Negative low temperatures high temperatures temperatures

Reaction to Positive Positive hPositive,mexceptua Nodata Nodata humidity high temperatures

Reaction to No data Positive Positive No data No data temperature_

Water loss High High Limited Limited Very limited

D Decrease in size of tegumental glands -. Trends Reaction to light becomes more important than reaction to humidity m in Figure 7. Terrestrialisopods are found in a full range of soil ecologies. Although their physiology and anatomy shows some specializationin the various habitats, it is behavioraladaptation that largely accounts for their success under very different conditions. (Data for the chart taken from Warburg,1968) own (Figures 6A & 6B). If conditions are too dry they 7) may be elicited by an assortment of stimuli in the will desicate quickly and if too moist they will suc- environment including light, temperature, relative cumb to fungi. Brood mortality in Paris' study was humidity, chemicals, vibrations, day length and the 7-8 percent. Young pill bugs are nearly white and behavior of other organisms. become progressively darker in successive moults, eventually turning a leaden gray or gray-blackwith Copingwith WaterLoss and Surplus sulfur-yellow spots. Pill bugs use nearly all their behavioral options in At one year of age females are ready to breed. Al- dealing with water economy as it is a centralproblem though one-year females are the largest part of the in living on land. Loss of water is a function of air breeding population, they are out-produced by two- temperature, relative humidity, rate of evaporation year individuals which have largerbroods. Paris'Cal- and the nature of the substrate. A pill bug's major ifornia population replaced itself every four to five mode of dealing with this problem as well as others years. is to move. It can move toward desirable conditions, away from undesirable ones, and move in circles if it The Pill Bug Solution likes things the way they are. The speed of move- ment reflects the nature and severity of the stimulus. The pill bug's solution, not only to surviving on In 1964, Warburg studied A. vulgare'sresponse to land with a rather meagre collection of physical adap- light, temperature and humidity and found a com- tations but also to outcompeting competitors in its plex interaction among the three variables among soil megafauna niche, has been to develop a simple, several species of terrestrialisopods in different hab- but effective repertoire of behavior. That repertoire itats. Figure 7 partiallysummarizes some of his find- includes locomotory activity: moving from place to ings. place; rolling up (conglobulating),which pill bugs but A pill bug's response to light is diminished toward not all terrestrialisopods can do; bunching behavior; sunset. At high temperatures, also, movement is burrowing and a preference for contact with surfaces faster and in a straight line, whereas at moderate and abdominal movements. These behaviors (Figure temperatures there is more turning, which tends to

14 THE AMERICAN BIOLOGY TEACHER, VOLUME 48, NO. 1, JANUARY 1986 keep the animals in more hospitable temperature between 20 and 30 degrees centigrade was optimal ranges. for aggregation. Pill bugs can actively take up droplets of water if Pill bugs can adapt also to temperatureextremes if they become dried out. You can observe them in a given some time to acclimate. Kaestner (1970) says petri dish, rhythmically contracting their abdomens that if A. vulgareare collected at low temperatures and drawing water up between their tail projections and kept two weeks at a temperature of 30 degrees as if through a straw. Grooves running from the base centigrade they will survive thirty minutes at 41 de- of one leg to another carry water the full length of grees centigrade whereas non-heat-adapted animals the body on either side. Fanning motions of the pleo- will die right away. pods speed the process. A drop of colored water placed on a pill bug's back soon ends up in these Respiration lateral grooves-collectively called a water transport Respirationis an activity that is, perhaps, least sub- system-and is carried toward the head where they ject to supplementation by behavioraltechniques, but can drink it. some terrestrialisopods do increase the flow of air Getting rid of excess water is a matter of evapora- over their pleopods by movements of the abdomen. tion and seems partiallyto dictate pill bugs' nocturnal Upward movement draws air in where it enters air rid of accu- behavior, allowing them to get moisture spaces created between pleopod exopodites at the Downloaded from http://online.ucpress.edu/abt/article-pdf/48/1/9/41822/4448178.pdf by guest on 01 October 2021 mulated in their daytime burrows. Pill bugs quickly junction between the thicker part (that contains the loose water from the ventral side of the abdomen pseudotracheae) and the thinner, laminar portion. where the respiratory organs are located. Just Downward movement of the abdomen expels the air. keeping the abdomen flat to the ground greatly re- Oxygen diffuses directly across the moist mem- duces water losses. Thus, it's not surprisingthat they branes. are thigmotactic-prefer to be in contact with some- thing on all sides. They also tend to bunch with other While insects may represent the pinnacle of ar- pill bugs although Friedlanderhas shown that they thropod adaptation to a terrestrialenvironment and will prefer moist areas without contact with other pill spiders can claim a close lineage to the first terrestri- bugs to dry areas with contact. A pill bug's tendency nauts in the animal kingdom, pill bugs and their kin to aggregate is regulated by more than thigmotaxis, have taken the basic body plan and "be- however. Kuenen and Nooteboom, in 1963, showed haved" their way into an important part of soil ecol- that pill bugs are attracted to each other's odor ogies. They are excellent subjects for studying how more so as they get dryer. It seems to be this behavior the interplay of environmental conditions affects an- which gets them back to shelter before daybreak. imal behavior. At least that can be your excuse next The behavior which gives a pill bug its name-the time you put one on your hand and watch him roll ability to roll up into a pill-like shape-also helps up. conserve water although whether that is more im- portant than its protective function is debatable. References Other types of terrestrial lack the isopods ability. Allee, W.C. (1926). Studies in animal aggregation:causes and effects of bunching in land isopods. Journalof Exper- TemperatureExtremes imentalZoology, 45, 255-277. Barrington, E.J.W. FRS. (1967). Invertebratestructure and Overheating, independent of any water loss in- function.Boston: Houghton Mifflin Co. volved, is a problem more severe for land organisms Clarke,K.U. (1973). Thebiology of theArthropoda. New York: than their water-based relatives. Most terrestrialis- American Elsevier Publishing Company, Inc. opods move away from light, which tends to keep Cloudsley-Thompson, J.L. (1961). Land invertebrates. them in shaded, cooler places. Pill bugs are some- London: Methuen and Co Ltd. what unusual in this regard as they Cloudsley-Thompson, J.L. (1968). Spiders,scorpions, cen- are photopositive tipedesand mites, Oxford:Pergamon Press Ltd. except at high temperaturesand humidity. However, Dallinger, R. & Wieser, W. (1977). The flow of copper Warburg(1968) concludes from his studies that light through a terrestrialfood chain. Oecologia(Berl.), 30, 253- is "mainly a token stimulus important more as a clue 264. for other factors, and with little over-all physiological Edney, E.B. (1968).Transition from water to land in isopod effect in isopods." crustaceans,American Zoologist, 8, 309-326. Foelix, R.F. (1982). Biologyof spiders.Cambridge, MA: Har- As mentioned earlier pill bugs move more quickly vard University Press. and in straight lines from areas of high temperature. Hals, G.D. & Beal, K.G. (1982). Death feint and other re- Their body temperature is also lowered by evapora- sponses of the terrestrialisopod, Porcellio Scaber. Ohio tive cooling. Their nocturnal behavior makes them Journalof Science,82(2), 94. active in the cooler, nighttime hours. Bunching be- Hassall, M. & Rushton, S. (1982). The role of coprophagy in the feeding strategies of terrestrialisopods, Oecologia, havior should also result in more consistant collective (Berl.), 53(3), 374-381. temperatures. Allee in 1926 found that a temperature Howard, H.W. (1940).The genetics of Armadillidiumvulgare

PILL BUG BIOLOGY 15 Latr. I. A general survey of the problems. Journalof Ge- beneath them. (See Figure 8) In pill bugs, the tail end is netics,40, 83-108. always rounded with a plate-like telson and uropods. A Huxley, T. (1878). Anatomyof invertebratedanimals. New good, inexpensive general reference which keys out York:D. Appleton and Co. common terrestrialisopods is Spidersand TheirKin, (1968), Juchault,P.P. & Legarnd,J.J. (1981).Contribution a l'etude New York:Golden Press. Cloudsley-Thompson(1961) has qualitativeet quantitativedes facteurs controlantle sexe good black and white pictures of differentspecies and Pratt dans les populations du Crustace Isopode terrestreAr- (1935)provides a more technical key. madillidiumvulgare latreille. Archives des Zoologie Ex- From a behavioral standpoint, if it rolls up chances are perimentale Generale, 122, 117-131. (Also see pp 65-74 you have a pill bug-in other words, a member of the in the same volume.). family Armadillididaeor Armadillidae.The common pill bug Kaestner,A. (1970).Invertebrate zoology crustacea vol III.New is Armadillidiumvulgare, a member of the former family. If York:John Wiley & Sons. you flip o'ne on its back you can see two pair of white Kuenan, D.J. & Nooteboom, H.P. (1963). Olfactoryorien- tracheallungs on the first two abdominalsegments. Mem- tation in some land isopods (Oniscoidea, Crustacea)En- bers of the latter family are found in desert regions and tomologieExperimentalia Applicata, 6, 133-142. have five pair of tracheallungs. Pill bugs have a hard time Lawrence, R.G. (1953). Thebiology of the crypticfauna of for- righting themselves once on their back and will eventually ests, Cape Town: A.A. Balkema. stop moving their legs. This makes them easier to work Levy, H.W. (1965). An unusual case of mimicry. Evolution, with than some of the sow bugs that don't roll up. These 19, 261-262. latter animals move more quickly and, since they tend to Moore, J. (1984).Parasites that change the behavior of their be flatter, can right themselves more easily. hosts. ScientificAmerican, 250, (5), 108-115. Culturing pill bugs is also simple, which is a plus for Downloaded from http://online.ucpress.edu/abt/article-pdf/48/1/9/41822/4448178.pdf by guest on 01 October 2021 Paris, O.H. (1963):The ecology of Armadillidiumvulgare (Is- their use in the lab. Howard (1940)used petri dishes with opoda, Oniscoidea) in Californiagrasslands. Ecology,43, damp filter paper on the bottom. To this he added dead 229-248. leaves and twigs to fill the dish. Four to ten individuals Pratt, H.S. (1935). Commoninvertebrate animals. Philadel- could be kept in each one. He also used #1 jars with an phia: P. Blakeston's Son and Co., Inc. inch of very wet cotton wool at the bottom. To this he Warburg, M.R. (1964). The response of isopods towards added dead leaves, twigs and beech wood leaf mold. temperature, humidity and light. Animal Behavior,12, For my first colony I found a well-populated source of 175-186. pill bugs in the clay soil beneath a cement drain spout cul- Warburg,M.R. (1968). Behavioraladaptations of terrestrial vert. With a shovel I removed the top inch or so of soil and isopods. AmericanZoologists, 8, 545-559. placed it in a five gallon aquarium and covered it with a Wieser, W. (1979). The flow of copper through a terrestrial piece of glass. From time to time I added a small amount food web. In Nriagu, Jo (Ed.) Copperin the environment, of fleshy fruit or a few of the local vine weeds that they partI: Ecologicalcycling, New York:Wiley, 325-355. seemed to feed on. If the soil looked dry I sprayed with water. The key is to give them sufficient moisture without encouraging a lot of mold growth. Pill bugs do eat some mold spores, but young pill bugs are susceptible to mold. Findingand Raising Pill Bugs Moist sand can be substituted for soil and is a little cleaner. Carrots (or almost any vegetable or fruit) can be used as How do you know a pill bug when you find it? The food and removed when they start to mold. terrestrialisopods, of which pill bugs are one example, in- clude rock slaters and sow bugs. Cloudsley-Thompson (1968) lists other common names-at least in England- such as bibble bugs, coffin cutters and tiggy hogs. Rock slaters are relatively primitive and inhabit shorelines. Sow bugs are common in leaf litter and humus on forest floors 1 2 e and pill bugs are populous in glasslands and deserts. All terrestrial isopods, however, share common traits. Their basic body shape is oval with an arched back, much UtUe like a lozenge cut in half lengthwise. They have a pair of eyes on the head which are not stalked like lobsters' and other decapod crustaceans'.They have two large antennae and two smaller antennules in front of them. The latter, however, are hard to see without magnification.The thorax has seven segments which are usually broaderthan the six following abdominal segments. Each thoracicsegment has a pair of walking legs. Thoracicsegments two to five have ventral plates that form the brood pouch in pregnant fe- males. The abdominal segments have appendages called pleopods. The inner branches or rami, form a surface, while the outer parts serve as a protective cover. In some species, including pill bugs, you will find bumps on some of the pleopods that are white in living animals. These are networks of respiratorytubules called pseudotracheae. Once you know you have a terrestrialisopod, it becomes a matter of knowing heads and tails. The antennae of ter- restrial isopods differ in the number of segments in the terminal portion, or flagellum. The tail ends differ in the shape of the terminal segment, or telson, and the uropods Figure 8. Making heads or tails of woodlice.

16 THE AMERICAN BIOLOGY TEACHER, VOLUME 48, NO. 1, JANUARY 1986