Terrestrial Isopods

Crustacea, Isopoda. Spanish: Cochinillas de la humedad, correderas (General). Portuguese: Tatuzinhos, baratinhas, bichos de conta (Brazil).

Many members of this large and diverse crustacean group (Mulaik 1960, Van Name 1936) are insectlike. They live in humid locations, often near water, including in tank plants such as bromeliads. Although they usually stay near moisture, they are capable of reproducing without depositing their eggs in free water. They may be particularly abundant in leaf litter and decaying vegetation, apparently feeding on the organic debris and fungi associated with such matter. Wood lice, which are found in decomposing leaf and wood litter, are the most familiar representatives. The group is also well represented in caves (Schultz 1981).

Terrestrial isopods are mostly small (BL 5—20 mm) and fairly uniform (onisci-form): oval in outline and somewhat flattened; body segments distinct and more or less equal, except the posterior whose lateral portions are strongly curved to the rear; anterior segments may be expanded winglike to the sides. The thoracic region makes up most of the body length and consists of seven segments, each with a pair of simple legs. Both pairs of antennae are short, but one pair is much shorter than the other. They have stout mandibles and well-developed eyes.

There are terrestrial members of only a few families of Isopoda in the Neotropics. Some of the more common are the somewhat amphibious Tylidae and Ligiidae (Ligia, fig. 4.1b; Ligidium), which live along the seashore within or just above the tidal zone and inland by watercourses—"sea roaches." These have extra long antennae. The near-blind Trichoniscidae are very small (BL up to 5 mm) and inhabit dense organic litter in caves.

Pillbugs (fig. 4.1c), so called because they can roll themselves into a ball, belong to the Armadillidiidae and Armadillidae. These are dull colored, often solid gray or gray-brown with lighter mottling. To resist moisture loss, the cuticle is usually tough and leathery; in some, it is quite rigid and also a good protective armor for the internal organs.

In nature, the true woodlice or Porcel-lionidae (sowbugs) (fig. 4.Id) and On-iscidae live in accumulations of dead decomposing plant matter. They are also abundant, sometimes very abundant, in gardens, greenhouses, and domestic situations where they are considered pests.

The literature is scant on these terrestrial arthropods; few faunal papers exist (Vandel 1972).


Mulaik, S. B. 1960. Contribución al conocimiento de los isópodos terestres de México (Isopoda, Oniscoidea). Soc. Méx. Hist. Nat. Rev. 21(1): 79-294. Schultz, G. A. 1981. Isopods (Oniscoidae) from caves in North America and northern South America. 8th Int. Cong. Speleol. Proc. 1: 551-552.

Vandel, A. 1972. Les Isopodes terrestres de la Colombie. Stud. Neotrop. Fauna 7: 147-172. Van Name, W. G. 1936. The American land and fresh-water isopod Crustacea. Amer. Mus. Nat. Hist. Bull. 71: 1-535.

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