Defenses of isopods include hiding/clinging/burying/nocturnalism, considered in this section, and PROTECTIVE EXOSKELETON & FAST RUNNING, SWIMMING, and CAMOUFLAGE considered in other sections. Some species of terrestrial isopods have repugnatorial glands (not dealt with here).

Several species of Idotea inhabit surfgrass and algal patches in the intertidal area.  They are strongly thigmotactic and their legs, especially those of adults, are well adapted to clinging onto rocks and seaweeds.

NOTE  reference to juveniles of rock slaters Ligia pallasii inhabiting intertidal growths of the green alga Enteromorpha spp. for protection can be found elsewhere in the ODYSSEY: TYPES & HABITATS

NOTE   lit. “touch oriented” G., referring here to a tendency of the legs to cling to anything that brushes against them

Idotea wosnesenskii crawling on seaweed,
possibly a mating pair. The male is the larger,
with proportionally larger, stronger legs 2X

In the supratidal beach areas of central California isopods Alloniscus perconvexus are attacked and eaten by larval and adult rove beetles Thinopinus pictus.  The isopods inhabit burrows in the sand during the day and emerge at night to forage.  The beetles attack from ambush positions among the micro-dunes and use their large, sickle-shaped mandibles to dismember the prey.  Craig 1970 Ecology 51: 1012. Photograph of Alloniscus courtesy Jonathan Wright, Pomona College, Claremont, California.

Larval rove beetle Thinopinus pictus attacks
and eats a semiterrestrial amphipod on the west
coast of Vancouver Island, British Columbia 1.5X

Terrestrial isopod Alloniscus convexus 3X

The semiterrestrial isopod Ligia pallasii and most other oniscidean isopods are nocturnal.  Advantages of this behaviour include water conservation and perhaps avoidance of daytime visual predators, such as spiders, birds, and shrews.  The tendency of Ligia and terrestrial species to aggregate during daytime also has water-sparing benefits. The graph shows the percentage of a population of L. pallasii at Seppings Island, British Columbia that are resting during a 24-h period. Only during nighttime are individuals actively moving around and feeding. Carefoot et al. 1998 Israeli J Zool 44: 463

Mature male Ligia pallasii 1.5X