Wilderness Underfoot: Isopods: creepy-crawlies for all regions

StoryImage( ‘/Images/Story//Auto-img-114305600613557.jpg’, ”, ‘An isopod – Caecidotea intermedius is found in shallow creeks throughout our region, usually clustering around rocks and debris. These creatures grow about a quarter-inch long (minus the tails). They’re an important source of food for predatory aquatic insects, fish and amphibians. In a remarkable study of this species, researcher Laura J. Hechtel and her associates found a tiny parasite by the name of Acanthocephalus dirus could alter the isopod’s behavior. When not infected, isopods in a tank full of minnows behaved normally, taking refuge from the hungry fish by hiding in debris. But when infected by the parasites, the isopods dropped their defensive strategies and walked out in the open, where they were easily eaten. This allowed the parasites to infect the minnows, their primary hosts!’);
StoryImage( ‘/Images/Story//Auto-img-114305602313557.jpg’, ”, ”);

From the Arctic to the Antarctic, these creatures thrive in the oceans, in freshwater, and even on land

Although the lowly isopods live mostly in marine (salt water) habitats, the ones we’re familiar with in Illinois are adapted to fresh water or life on land. Isopods aren’t insects; they aren’t even closely related to insects. These are crustaceans—the kin of crabs, lobsters, shrimp and crayfish.

The word isopod means “same footed.” These creatures are so named because, unlike many of their crustacean kin, they do not have specialized limbs—for example, they lack the large claws that have evolved in crabs and lobsters. In isopods, all five to seven pairs of legs are pretty much the same shape, best suited for simply creeping about.

With flattened bodies and plenty of legs, isopods are well adapted for crawling through debris—whether it’s under water or piled up on land. They have a taste for detritus, the organic waste of plants and other dead organisms, but they’ll also nibble on live plants and arthropod eggs.

Like other crustaceans, isopods breathe through book gills at the base of their legs. Even terrestrial isopods have gills, and these must remain moistened or the creatures will die. Humidity levels lower than 50 percent can cause them to dehydrate in less than a day. Our most familiar land-based isopods—the sow bug (also known as a wood louse) and the pill bug—are easily found under rocks, logs, and leaf litter, where moisture is plentiful. They avoid sunlight and dry locations.

The pill bug has acquired the name “roly-poly” because of the way it curls into a perfect little ball to protect itself when disturbed. This is probably a splendid defense mechanism in the natural world, but the same trick makes this poor creature all the more interesting to any young child who sees it!

Isopods have been affectionately called “the other marsupials” by Australian researchers Alastair Richardson and Roy Swain because the creatures carry their offspring in pouches on their undersides.

From the MArch 22-28, 2006, issue

Enjoy The Rock River Times? Help spread the word!