Journal of the Minnesota Academy of Science

Volume 38 Number 2 Article 9

1972

Terrestrial Isopods of Minnesota

James E. Sargent University of Minnesota, St. Paul

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Recommended Citation Sargent, J. E. (1972). Terrestrial Isopods of Minnesota. Journal of the Minnesota Academy of Science, Vol. 38 No.2, 88-92. Retrieved from https://digitalcommons.morris.umn.edu/jmas/vol38/iss2/9

This Article is brought to you for free and open access by the Journals at University of Minnesota Morris Digital Well. It has been accepted for inclusion in Journal of the Minnesota Academy of Science by an authorized editor of University of Minnesota Morris Digital Well. For more information, please contact [email protected]. feet in 2 to 3 minutes. After this time the fly cannot be this shallow body of water certainly freezes through to induced to move for another 5 to IO minutes. the bottom. The succeeding generation of larvae enter the winter season in the last or next to the last instar. (Sampling of References this pond on October 19 with the water temperature at JAMES , MAURICE T. and STEYSKAL, GEORGE C. 1952. A 38°F. showed mo:-e of the latter than the former). A re­ Review of the Ncarctic Stratiomyini (Diptera: Stratio­ turn to this site on May l with the water temperature at myidae). Ann. Ent. Soc. Amer. 45: 385-412. 32 ° F. and thin ice on the surface yielded two last instar JOHANNSEN, 0 . A. 1922. Stratiomyiid larvae & puparia larvae. These were in about 3 ½" of water and did not of the Northesastero states. J. N .J. Ent. Soc. 30: 141- have the usual respiratory bubble at the caudal end. They 15 3. seemed dead until allowed to warm up, at which time JoIIANNSEN, 0. A. 1935. Aquatic Diptera. Pt. ll. Or- they became active. It is assumed that the larvae were in thorrapha-Brachycera and Cyclorrapha. Cornell the soil of the bottom of the pond during the winter as Agr. Exp. Sta. Mem. 177: 1-62.

ENTOMOLOGY Terrestri·al isopods of Minnesota

JAMES E. SARGENT'-'

ABSTRACT - Eight of terrestriol isopods (sub-order Oniscoidea) were collected in Minnesota. Six of them had not been recorded previously. Observations on habitat, distribution, size and coloration were noted. An analytical key to the species within the state is included.

Because of their abundance and wide-spread distri­ acterized by a permeable cuticle and fourteen legs. The bution, the terrestrial Jsopoda (sub-order Oniscoidea) name "," meaning "equal feet," is more accurate are familiar to many people, if only by visual recognition descriptively for the terrestrial isopods than for the aqua­ (Figures 1-b and 2). Prior to this study, little was known tic isopods. of the isopods of Minnesota. Arcangeli ( I 932) reported Since these live on land, their water bal­ finding convexus (DeGcer) at St. Paul and ance must be protected. Commonly they will live in damp Frontenac; and Gunderson ( 1962) collected Tracheo­ places, where there is less loss of moisture through their niscus rathkei (Brandt) at Stillwater. pseudotrachea and gills (Figs. 1-d, 1-e). Aggregation is The purpose of this study in 1971 was to determine not uncommon in suitable places, or as a mans to con­ what species commonly occur in the state and to record serve moisture (Allee, 1926). Some species can also roll observations concerning their natural history and distri­ up and are thus called "pill bugs" (Fig. 2). This may bution. Specimens were collected in a short search of an also retard dessication. Molting is an espccia11y crucial area. These and unidentified specimens in the Entomol­ event because of the possibility of large water losses. ogy museum at the University of Minnesota were identi­ Eggs and young arc kept moist in a brood pouch un­ fied on the basis of descriptions in Yan Name ( 1936) til they arc born alive. As they grow they molt, but and Hatchett ( 1947). The museum specimens are sum­ only half of the cuticle at once. The split occurs between marized in Table 1. the fourth and fifth segments of the thorax with the pos­ The specimens collected in this study, besides those terior half first and then the anterior half up to several listed in Table I, included Armudillidium m1satum days later. In the adult isopod molting takes place about Budde-Lund and Linnaeus (Table JI.). every two months. ( Figures 1-a-1-c). These findings indicate distribution Reproduction usually does not begin until after the within counties of all the species recorded and coilected. An analytical key to the species found in Minnesota ac­ second year (Heeley, 1941). Generally, fertilization companies this paper. takes place only once a year but several broods may be produced. Heeley ( 1941) observed that an average Biology of terrestrial isopoda brood for P. scaber was 24 individuals and for A. vul­ Tsopods make up a large part of the Class Crustacea. gare was 113 individuals. They live to about three years The external anatomy of the terrestrial isopods is char- of age.

JAMES E. SARGENT received the B.A. Degree from Most activities of the terrestrial isopods take place in Hamline University (where this study was initiated). darkness ( Abbot, 19 l 8), but their response to humidity Currently be is Assistant Extension Entomologist in the Department of Entomology, Fisheries and Wildlife ~t levels is stronger than their reaction to light. (Wal off, the University of Minnesota, St. Paul. 1941). The preference for damp habitats varies between 88 Tlie Minnesota Academy of Science species. Desiccation will often cause terrestrial isopods to absorb moisture my mouth and anus from food or free Terrestrial lsopods surfaces (Edney, 1954). of Minnesotcr The terrestrial isopods are scavengers, feeding pri­ I Uropods extending beyond the terminal abdominal marily on dead vegetation. The amount of food eaten by segment (Figs. 1-a, 1-d and 2) ------3 them is many times the amount assimilated (Hubbell, et l' Uropods not extending beyond the terminal ab- al., 1963). The poor digestive efficiency means that they dominal segment (Figs. 1-e, 2, 11) -~---- 2 have an important part in the ecosystem by fragmenting 2(1') Small squarish lobe extending beyond head anteriorly, and breaking down dead organic material (White, 1968). tiny v-shaped notch in front of head (Fig. 1-a) nasatum Bude-Lund Thus they could be considered beneficial. 2' Without lobe or notch (Latreille) History from geological times 3(1) Three-seg:mented antenna} flagellwn (Fig. 7), white The Isopoda are old, probably going back in geologi­ ventral surface with 5 pair ve1·y faint pseudotrachea cal history as far as the second half of the Paleozoic Era. Oniscus asellus Linneaeus The are said not to appear until the upper 3' Two-segmented antenna} flagellum (Figs. 5, 6), pseu- Eocene (Yan Name, 1936). The terrestrial forms dotrachea distinct ______4 evolved from marine forms and have evolved back to an 4(3') Antenna} joints prominently banded with white (Fig, 2), frosty narrow body with abruptly narrow abdo­ aquatic habitat in a few instances (Ellis and Williams, men, second flagellar segtnent shorter than first, 2 1970). Few Oniscoidea were endemic in America. They pair distinct pseudotracrea, very quick are predominantly tropical, but since being established in pruinosus (Brandt) have become quite common. This wide­ 4' Antenna! joints not prominently banded with white, spread distribution of some of the terrestrial isopods in other characteristics variable ______5 North America seems to be the result of having relatively 5(4') Dorsal surface of body smooth and strongly convexed few natural enemies ( Y andel, 1949). (Fig. 2), capable of rolling into a •ball (Fig. 2), flagellar segments equal length, 5 pair distinct pseu- The species collected in this Minnesota study are Old dotrachea ______Cylisticru convexus (DeGeer) World species introduced into America by human agen­ 5' Dorsal surface not as above, incapable of rolling cies, Walker (1927) believes that of the Canadian Onis­ into a bal~------6 coidea, all are introduced. As far as their distribution in 6(5') Five pair of pseudotrachea, posterior pairs becoming Minnesota is concerned, they are most commonly found less distinct (Fig. 8), flagella narrow with second seg­ near areas disturbed by man, including basements, green­ ment longer than first, seventh leg of male with prom­ inent keel-like expansion on dorsal border of third houses, dump grounds and wooded pastures. segment from distal end Tracheoniscru rathkei (Brandt) Distribution and habitat 6' Two pair of pseudotrachea, flagella not as above, Tracheoniscus rathkei (Brandt) was the most fre­ no keel-like expansion on seventh male leg ______7 quently collected terrestrial isopod in the state. Eberly 7 (6') Double longitudinal row or yellow patches on dorsal (1953) believes that it is the commonest isopod in In­ surface, head and abdomen distinctly darker than diana. Hatchett (1947) has 209 records of T. rathkei in thorax, ventral abdominal plates dark, second flagellar segment longer than first, slight tubercles Michigan to support the same idea. He concludes that it spinicornis Say is not specific in its habitat preference, thus accounting 7' Not as above, color usually dark grey or red, pro­ for its wide distribution. It was found in Minnesota un­ nounced tubercles on dorsal surface including head, der dead bark, logs, boards, rocks, asphalt chunks, ma­ short equal-segmented stout flagellum (Fig. 1-b). nure, dead rushes, humus, debris, culverts, and railroad Porcellio scaber Latreille ties. It was collected most often in areas characterized by hardwoods. These areas were more or less disturbed hab­ itats where pasturing or construction had taken place. It of the world, being recorded further north than any other was found near human dwellings in only a few instances. terrestrial isopod (Yan Name, 1936). It is widely dis­ (DeGeer) (Fig. 2) is also very tributed in the United States, being reported in every ma­ commonly found in Minnesota. Walker (1927) states jor paper published. It can be found in Minnesota under that this is the most common terrestrial isopod in eastern dead bark or logs, under stones, and in plant litter, but Canada. It is also common in Iowa (Longnecker, 1924 ), usually around building foundations, or in basements. (Hatchett, 1947), and Indiana (Eberly, 1953). In Min­ This species, although not as widely distributed in rural nesota, the specimens were collected from greenhouses, areas as other species, is so common in human settle­ basements, mushroom caves, storm sewers, city dump ments that many people consider it as the representative grounds, and near water bodies under debris, but gener­ terrestrial isopod. It is often called basement bug, water ally near human habitations. Hatchett ( 194 7) states that bug, or sowbug. this species seems to prefer a more moist situation than Procellionides pruinosus (Brandt) is cosmopolitan and do other terrestrial isopod species in Michigan, as also occurs mostly near human habitations throughout the seemed true in the Minnesota collections. United States. Walker ( 1927), though, only reports one Poree/Lio scaber Latreille (Fig. 1-b) is a native of Eu­ sighting in Southern Canada, and Judd ( 1965) reported rope and has followed man throughout the greater part moderate occurrence in greenhouses in the vicinity of Journal of, Volume Thirty-eight, Nos. 2 and 3, 1973 89 the dump were not limiting factors. P. pruinosus appar­ F/6./-a ently does have a higher tolerance of low humidity as in­ dicated by Hatch (1947) and this collection. Armadillidium vulgare (Latreille) is the commonly known "pillbug" of the southwestern United States, al­ though C. vonvexus and Budde­ Lund can also roll into a ball. It is common outdoors in the South but is rarely found outside of greenhouses in

FLAGELLUM

PSEUDOTRAC HEA

F/6. /·d Fl~ 1-e

FIGURE 1. Some distinguishing features of various terrestrial isopods. 1-a.-Head of Armadillidium nasa­ tum Budde; 1-b-Porcellio scaber Latreille; 1-c-anten­ na of Onisus asellus Linnaeus; 1-d - Ventral view of Tracheoniscus rathkei (Brandt) ~ abdomen; 1-e-ven­ tral view of Armadillidium vulgare (Latreille)

TABLE II. Terrestrial Isopods of Minnesota. Number Average Maximum Collection Species Collected Size (mm) Length (mm) Sites Oniscus asellus Linnaeus ...... 10 8.4 14 2 Armadillidium nasatum Budde-Lund . . . 492 6.4 14 5 Porce/lio spinicornis Say ...... 134 8.4 14 11 Armadillidium vulgare (Latreille) . .... 236 7.8 14 17 Porcellionides pruinosus (Brandt) 177 7.5 11 24 Porcellio scaber Latreille ...... 652 8.6 15 37 Cylisticus convexus (DeGeer) ...... 547 8.5 13 60 Tracheoniscus rathkei (Brandt) ...... 1251 8.l 13 137

Journal of, Volume Thirty-eight, Nos. 2 and 3, 1973 91 ana (Eberly, 1953), or Canada (Walker, 1927), Min­ populations of ground forms on islands in the St. nesota may be a transitional zone between the ranges of Croix River. Masters Thesis. University of Minnesota. some of the species. HATCH, M. H. 1947. The chelifera and lsopoda of Wash­ In the collection of specimens, body length and color ington and adjacent regions. Univ. Wash. Publ. Bull. were recorded (Table H). There were not any unusual 10(5):155-274. results except in two instances. T. rathkei females were HATCHETT, S. P. 1947. Biology of the Isopoda of Michi­ predominantly brown or brown-red while the males were gan. Ecol. Monogr. 17 ( 1) :47-79. almost always black (Table Ill). There was variation in HEELEY, W. 1941. Observations on the life-histories of between those colors, making a more objective measure­ some terrestrial isopods. Proc. Zoo!. Soc. London. ment desirable. 111 :79-149. Also, more than twice as many females as males were HUBELL, s. P., A. SIKORA, and 0. H. PARIS. 1965. Ra­ found (Tables III, IV). Since the sample size at each diotracer, gravimetric and calorimetric studies of di­ collection site was small validity of these results may be gestion and assimilation rates of an isopod. Health questioned as to possible bias in the collection method Physics 11: 1485-1501. regarding size or some other factor. Because the females JUDD, W.W. 1965. Terrestrial sowbugs (Crustacea:Iso­ were larger on the average than the males, their more poda) in the vicinity of London, Ontario. Can. Field­ noticeable size could account for the above results. For Nat. 79(3): 197-202. P. scaber, however, the results were the opposite, so a LONGNECKER, M. 1924. The terrestrial isopods of Iowa. firm conclusion is difficult. (Table IV). Proc. Iowa Acad. Sci. 30: 197-199. RICHARDSON, H. 1905. A monograph on the isopods of References North America. Washington, U.S. Nat. Mus. Bull. 54: 1-727. ABBOT, C. H. 1918. Reaction of land lsopoda to light. SCHULTZ, G. A. 1963. Distribution and establishment of J. Exp. Zool. 27: 193-246. a land isopod in North America. Sys. Zool. 10: 193- ALLEE, W. C. 1926. Studies on aggregations: 196. causes and effects of bunching of land isopods. J. Exp. VANDEL, A. 1949. La faune nord-atlantique. Rev. Fran­ Zool. 45:255-277. caise Ent. 16: 1-11. ARCANGEL!, A. 1932. Isopodi terrestri raccolti dal Prof. VAN NAME, W. G. 1936. The American land and fresh­ Silvestri nel Nord-America. Boll. Lab. Zool. Gen. water isopod Crustacea. Bull. Amer. Mus. Nat. Hist. Agrar. Portici. 26: 121-141. 71:1-535. EBERLY, W. R. 1953. The terrestrial isopods (Oniscoi­ WALKER, E. M. 1927. The woodlice or Oniscoidea of dea) of Indiana. Proc. Indiana A cad. Sci. 63: 272-277. Canada (Crustacea, Isopoda). Can. Field-Nat. 41: EDNEY, E. B. 1954. Woodlice and the land habitat. Bio. 173-179. Revs. 29 : 185-219. WALOFF, N. 1941. The mechanisms of humidity reac­ ELLIS, P. and W. D. WILLIAMS. 1970. The biology of tions of terrestrial isopods. J. Exp. Biol. 18: 115-135. Haloniscus searle; Chilton, an oniscoid living in Aus­ WHITE, J. J . 1968. Bioenergetics of the tralian salt lakes. Aust. J. Mar. Freshwater Res. 21 Traacheoniscus rathkei Brandt in relation to litter de­ (1) :51-69. composition in a deciduous forest. Ecology. 49: 694- GUNDERSON, R. w. JR. 1962. The effects of flooding on 704.

92 The Minnesota Academy of Science