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The terrestrial isopods (Oniscoidea) of Louisiana. (Short Communication).

ABSTRACT--To date, 8 species of terrestrial isopods (Oniscoidea) have been found in Louisiana. The majority are European species accidentally imported by man. They are found throughout the state except in the coniferous woodlands. They play an important role in the development of soil.

Key words: terrestrial isopods, Louisiana.


If one consults the two standard works on North American isopods (Richardson 1905, Van Name 1936), one will find few if any references to isopods in Louisiana. Commonly known as woodlice, sow bugs or pillbugs, they are widely distributed through the state. Terrestrial isopods are the only large group of Crustacea to become adapted for life on the land.

Since the 1970's, the author has made a number of trips to Louisiana collecting in all ecological areas of the state. In general it may be said that in some areas they are very abundant while in other areas they are rare or absent. Terrestrial isopods are found where the humidity is relatively high; they are nocturnal and cryptozoic. In dry weather they can be difficult to find as they can burrow into soil and deep humus.

Terrestrial isopods are found under stones, rotting logs, in deciduous humus, damp decaying vegetation, compost, manure and dump heaps. The soil must have sufficient calcium to enable them to develop their chitinous exoskeleton that is high in calcium carbonate (Sutton 1972). Such soils tend to be neutral or alkaline in pH and rich in micro-decomposers.

The relationship of terrestrial isopods in the ecosystem has not been understood until recently. In the past, it has simply been stated that isopods do little more than triturate the litter in which they live. In recent years, soil scientists have shown that they play an important role in the breakdown of litter and wood residues. Sutton (1972) has found that lycosid spiders, centipedes, and shrews are predators.

Most of the species of isopods found in Louisiana have been imported from Europe (Van Name 1936). Vandel (1949), writing on the North American distribution, stated that continental drift may explain the presence of some European isopods in North America. Studies on Tracheliis rathkei (Brant) (Rapp 1988) indicate that it may be circumboreal. In Louisiana, no collections were made in greenhouses where synanthropic species may occur. In most cases they have been imported with plants.

The majority of collecting was done in rural areas. Urban areas were avoided because these areas have been changed by man and do not represent the natural areas. In general, highly cultivated agriculture areas do not support a population of isopods, except around farmhouses. A number of collecting trips were made in the coniferous area but no isopods were found. In general it may be stated that large numbers of isopods occur in Louisiana, but only in the proper ecological niches.


Unfortunately there are no recent works on the terrestrial isopods of the United States. The two major works, Richardson (1905) and Van Name (1936) are the best references. Muchmore (1990) has published a key to genera that is useful. The checklist follows the sequence proposed by Holdich et al. (1984). All specimens are deposited at the Illinois Natural History Survey, Champaign, Illinois.


Family Ligiidae

Ligidium mucronatum Mulaik

ASCENSION Parish: Gonzales (type locality), Roosevelt State Park. Specimens in the American Museum of Natural History. See Mulaik 1942.

Family Trichoniscidae

Trichoniscus humus Mulaik

ST. LANDRY Parish: West of Eunice (type locality). Specimens at the American Museum of Natural History. See Mulaik 1942.

Family Armadillididae

Armadillidiun nasatum Budde-Lund

WASHINGTON Parish: Franklinton, 3 Apr. 1992.

Armadillididium vulgare Latreille

ASCENSION Parish: Sorrento, 11 Nov. 1992; CALCAUSIEU Parish: Gillis, 23 Apr. 1986; CAMERON Parish: Bradley Beach, 22 Apr. 1987; Hackberry, 22 Apr. 1987; Holly Beach, 22 Apr. 1987; Johnson Bayou, 17 Sept. 1990; CATAHOUA Parish: Jonesville, 5 Apr. 1992; CONCORDIA Parish: Ferriday, 4 Apr. 1992; DESOTA Parish: Logansport, 30 Mar. 1992; Mansfield, 30 Mar. 19 1992; IBERIA Parish: Jeanerette, 18 Sept. 1990; Weeks Island, 23 Apr. 1987; LAFOURCHE Parish: Cut Off, 4 Apr. 1986; Klondy Key, 24 Apr. 1987; Lockport, 24 Apr. 1987; NATCHITOCHES Parish: Cypress, 18 Apr. 1986; Flora, 8 Apr. 1986; Natchitoches, 17 Apr. 1986; ORLEANS Parish: 14 Oct. 1986; PLAQUEMINE Parish: Belle Chase, 23 June 1994; Myrtle Grove, 20 Apr. 1986; Nairn, 20 Apr. 1986; Port Nickel, 20 Apr. 1986; Venice, 20 Apr. 1986; West Pointe A La Hache, 20 Apr. 1986; POINTE COUPEE Parish: Lottie, 11 Nov. 1992; SABINE Parish: Fisher, 25 Apr. 1986; Pleasant Hill, 30 Mar. 1992; ST. CHARLES Parish: Ama, 1 Oct. 1973; Norco, 1 Oct. 1973; Waggaman, 1 Oct. 1973; ST. HELENA Parish: Greensburg, 3 Apr. 1992; ST. JOHN THE BAPTIST Parish: Lapace, 1 Oct. 1973; ST. MARY Parish: Franklin, 34 April 1986; ST. TAMMANY Parish: Mandeville, 30 Sept. 1973; St. Joe, 30 Sept. 1973; Slidell, 30 Sept. 1973, 20 Mar. 1991; TANGIPAHOE Parish: Arcola, 3 Apr. 1992; Fluker, 3 Apr. 1992; TENSAS Parish: Waterproof, 4 Apr. 1992; TERREBONNE Parish: Humphreys, 12 Oct. 1986; VERNON Parish: Leesville, 30 Mar. 1992.

Family Porcellionidae

Porcellio laevis Latreille

CAMERON Parish: Holly Beach, 22 Apr. 1987; TENSAS Parish: Waterproof, 4 April 1992.

Porcellio scaber Latreille

BEAUREGARD Parish: Longville, 25 Apr. 1986; NATCHITOCHES Parish: Flora, 18 Apr. 1986.

Porcellionides pruinosus (Brandt)

CONCORDIA Parish: Vidalia. 4 Apr. 1992; MADISON Parish: Waverly, 16 Sept. 1987; ORLEANS Parish, New Orleans, 14 Oct. 1986; TERREBONNE Parish: Chauvin, 24 Apr. 1987.

Family Trachelipidae

Trachelipus rathkei (Brandt)

CAMERON Parish: Holly Beach, 22 Apr. 1987; LAFOURCHE Parish: Klondyke, 24 Apr. 1987; ST. TAMMANY Parish: Slidell, 30 Sept. 1973.

Hypothetical Species

Family Ligiidae

Ligidium baudiniana Miline-Edwards
 I was never able to collect this large isopod along the Louisiana coast. It
 is abundant along the Mississippi and Texas coast on breakwaters and under
 debris. This species should occur along the Gulf coast of Louisiana (Rapp
 and Rapp 1989).


HOLDICH, D.M., R.J. LINCOLN, AND J.P. ELIAS. 1948. The biology of terrestrial isopods: Terminology and classification. In Symposium of the Zoological Society of London. No. 53.

MUCHMORE, W.B. 1990. Terrestrial isopods. In Soil biology guide, John Wiley & Sons.

MULAIK, S. AND D. MULAIK. 1942. New species and records of American terrestrial isopods. Bull. Univ. of Utah 32(6):1-23.

RAPP, W.F. 1988. Trachelipis rathkei in North America. Isopoda 2:15-19.

RAPP, W.F. AND J.L.C. RAPP. 1989. Ligia baudiniana on the Gulf Coast of the United States. Isopoda 3:15-18.

RICHARDSON, H. 1905. A monograph of the isopods of North America. U.S. National Museum Bull. 54. 727 pp.

SUTTON, S. 1972. Woodlice. Pp. 1-144. In Ginn & Co., London.

VAN NAME, W.G. 1936. The American land and freshwater isopod Crustacea. American Museum of Natural History Bull., Vol. 71. 535 pp.

VANDEL, A. 1949. La Faune Nord-Atlantique. Revue Francaise D'Entomologie. Vol. 16(1): 1-11.
William F. Rapp
87 South Main Street
Pittsford, NY 14534
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Author:Rapp, William F.
Publication:The Proceedings of the Louisiana Academy of Sciences
Geographic Code:1U7LA
Date:Jan 1, 2001
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