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The Rollicking Life of the Roly-Poly
They go by many names: roly-polies, pill bugs, potato bugs, sow bugs. But whatever you call them, those hard- shelled little critters lurking under logs in the backyard have an impressive repertoire of tricks and rather unexpected origins.

By Michael Purdy

When Katalin Szlavecz starts talking about a recent scientific meeting she attended in Europe, she pauses. "I get this look all the time--'You mean there are other people who study them?'" Szlavecz says, laughing. "Yes, there are! At the meeting in Crete, [there were] about 60 to 100 of us."

Szlavecz, a Hopkins research scientist in Earth and Planetary Sciences, specializes in the ecology of isopods, those small, pill-shaped gray bugs with a long collection of pseudonyms. She is the first to acknowledge that the segment of the general public that gives isopods the most attention probably hasn't yet started kindergarten. The young have less compunction about getting their hands (and anything else) dirty and are often fascinated by the ability some isopods have to roll up into a small gray ball when threatened. The rolling-up trick, admittedly one of the odder defenses employed by the menagerie of small performers living in the typical back yard, is just the beginning of the isopod's strangeness.

First off, many of the names for isopods are misnomers. Isopods aren't bugs or insects, they're crustaceans, the only relative of lobsters and shrimps to evolve into a completely terrestrial lifestyle. In addition, the sex life of isopods can be quite colorful. Suffice it to say that if the habits of some species were detailed, many people would call them unusual, some would call them amazing, and a few would call them perverts.

The aspect of isopod weirdness central to Szlavecz's research, though, is the fact that isopods "get around." In a field near a condominium in Baltimore, Szlavecz has discovered a species of Mediterranean isopods. The inauspicious little field is the only spot in North America where these Mediterranean isopods have been spotted. Szlavecz wasn't surprised by her discovery. She and her colleagues have been identifying non-native species of isopods and other arthropods, worms, and soil-dwelling creatures for years, and she knows the United States is teeming with them.

"These days, the introduced species mostly result from ornamental plants at greenhouses that have soil in the container from the native country," Szlavecz explains. It's a tradition that actually dates all the way back to when the first Europeans started coming to America. "The first American immigrants brought non-native species over because they brought their little apple trees and things like that with soil," Szlavecz says. "But also in the early ships the ballast was not water, it was soil." Soil ballast helped keep the ships sailable for the dangerous journey across the Atlantic, but once the ships arrived, sailors had to get rid of the soil to load up the treasures of the new world. Much of the dirt was shoveled onto shore. "So with that I'm sure a lot of soil organisms got unintentionally introduced," she says.

As part of her current field work with the Baltimore Ecosystems Study, a long-term ecological research project funded by the National Science Foundation, Szlavecz works to promote awareness of non-native species and the role people can play in spreading them. None of the introduced creatures she studies is likely to ever present an ecological or economic cause for alarm comparable to that of, say, the Cane toad in Australia or the Zebra mussel in the Great Lakes, but Szlavecz feels that knowing who these tiny invaders are and what they do is still a worthwhile goal.

"For many people, an earthworm is an earthworm is an earthworm," she says, "but there can be big differences in what different species of earthworms do, and that can have an effect on the ecosystem."

Return to September 2001 Table of Contents

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