Pill Bugs and Sow Bugs

     I often find little colonies of pill bugs and sow bugs under objects such as stones, boards and lawn ornaments I pick up from the ground in our yard.  I have also found pill bugs, also known as roly-polies, and sow bugs, frequently referred to as wood lice, on soil and fallen leaves under logs and limbs on woodland floors.  And I see them behind loose bark and in small cavities of still-standing trees.  All these places are moist, dark and sheltering; niches that keep these interesting little creatures from drying out, and safe from predators.
     When uncovered, or touched, pill bugs roll into small, tight balls so their hard, shiny exoskeletons or "shells" protect their legs and internal organs.  Sow bugs, however, can not curl into balls, but still rely on their hard shells for protection.
     Pill bugs and sow bugs are not bugs at all.  They're not even insects, but appear that way to some people.  These little, related isopods of woods, gardens and lawns are intriguing cousins to crustaceans, including crabs and shrimp.  In fact, pill bugs and sow bugs are the only crustaceans that live wholly on land across much of the world, including the United States; but in moist places where they can respire.
     Being related, appearing similar and sharing habitats, pill bugs and sow bugs have several characteristics in common.  Both species, as adults, are half an inch long, have dark-gray, segmented exoskeletons that protect and camouflage them in soil, dead wood and other dark niches they live in. Both kinds have seven pairs of legs, two pairs of antennae, two simple eyes and trachae-like lungs.  They emerge from damp shelters on summer nights to feed.  And mature females carry up to 100 eggs in pouches under their bodies until their young hatch.
     Being part of nature's clean-up committee, these related species are scavengers, decomposers, feeding mostly on decaying plant material.  But they also consume live plants, including fruits and berries, lettuce and so on, but usually cause little damage. 
     But these ancient crustacean cousins have a few differences, too.  Pill bugs' bodies are rounded and close up tightly, while those of sow bugs are more flattened and don't close tight. 
     A variety of small birds, plus shrews, skunks, small snakes, box turtles, toads, certain spiders, centipedes and other predatory creatures ingest many of these roly-polies and wood lice, making them part of several food chains.  That is another reason why these little crustaceans stay hidden most of the time.
     Pill bugs and sow bugs are interesting little critters that usually don't cause any harm to people.  But one usually has to look for them to acknowledge their presence.