Holy Moly, It’s a Roly-Poly!

Roly-Polies and other woodlice are easy to find, perform some amazing stunts and may have non-traditional families.

Isopods are among the most abundant creatures that you will find in a typical Lehigh Valley garden. They answer to about 20 different common names, including woodlice, sow bugs, pill bugs, potato bugs and roly-polies. Strictly speaking, isopods are not bugs. A quick leg count will reveal that isopods are not even insects. Insects have six legs and isopods have 14. Isopods are crustaceans, which makes them more closely related to crabs, shrimp, barnacles and lobsters. 

My favorite nickname for all the isopods that live on land and far from the beach is “woodlice.”  It is not a perfectly cromulent moniker, since they aren’t lice and they don’t eat wood. However, it’s broad enough to include our local land-loving isopods that can either curl up into a little ball (pill bugs a.k.a. roly-polies) or not  (sow bugs). 

Woodlice are not the only crustaceans that can live away from the watery depths. However, they are the only ones that I know of that can spend their whole lives on solid ground. Coconut Crabs and some other Hermit Crabs can live on dry land, but they still need to return to the ocean to reproduce. Only about half of the 10,000 known isopod species live on land, the rest prefer freshwater or marine habitats.

One species of giant isopod that roams the ocean floor can measure up to 30 inches long. One leviathan of the abyss was photographed by workers on an oil rig. It was thought by many to be an April Fools prank, but it wasn't. Can you imagine them scampering around on your back lawn? As long as they left my tulip bulbs alone, I would probably welcome them.

The Common Woodlouse (Armadillidum vulgare) is also known as the Roly-Poly or Pill Bug. As their Latin name suggests, they can roll up like an armadillo. They are familiar, but by no means vulgar. Their advanced yoga skills have the advantage of protecting them from enemies, like ants, while also preventing them from drying out.

Sow bugs cannot roll themselves up into a little ball. Try to make them do it, you’ll see. Two common species of sow bugs in the Lehigh Valley are the European Sow Bug (Oniscus asellus) and the Rough Sow Bug (Porcellio scaber).  Not to be outdone, they have a very special trick that the Roly-Polies cannot pull off. They can sponge up water from the ground with a pair of narrow appendages called uropods, which appear to protrude from their little bottoms.

Although woodlice live on terra firma, they can never be very far from fresh water. They breathe through gills at the bases of their legs. In order to work properly, the gills need to be constantly moist. Unlike insects, they do not have protective waxes and oils on their exoskeleton to prevent water loss. Nor do they have the nifty water-saving internal air tubes that insects have. This is why woodlice are usually found in damp places, like under flower pots.

The European origins of our most common woodlice are explored in by Patricia Gadsby in a Discover Magazine article (August, 1999). Woodlice were originally introduced to both coasts by visitors arriving from different regions of Europe. Woodlice in the Southwestern United States bear the genetic markers of their Spanish ancestors. Eastern woodlice are more likely to have relatives back in England. Thus, the shadows of American colonial history are still detectable in the population genetics of our introduced woodlice. Gadsby's article also delves into other crucial information about woodlice, like how they taste.

Woodlice can be fabulous companion animals. With proper care and feeding, they can be kept alive for more than three years. They love potatoes. Almonds make for a tasty treat to be enjoyed on special occasions. Ideal containers are clear plastic boxes containing a thin layer of soil, a few pieces of bark and some leaf litter. Throw in some grated carrot every week, and spritz them lightly with water as needed. Don’t water them too much, since woodlice are just as easily killed by drowning as they are by drying out. Unlike most other companion animals, woodlice can be safely released back into the wild when they retire.

Much easier to keep than kangaroos, woodlouse mothers still have the endearing quality of keeping their unborn babies in a little belly pouch, called a marsupium.  The mothers will carry their precious cargo around for up to a month. After birth, the newborn woodlice will head off immediately to seek their own fortunes.  They don’t get any motherly coddling like baby . Woodlice are generally ready to reproduce when they are about 2 years old.

Female Common Woodlice (Armadillidum vulgare) do not need find a male partner in order to have little bundles of love. However, solo females will only be able to have daughters. There are a few strains of a gender-bending bacterium called Wolbachia that can inhabit the cells of some woodlice. This infection can cause male woodlice to develop into females, by knocking out the gland that produces a male hormone. Transgendered woodlice are capable of reproducing, but with a catch. Most of their offspring will be Wolbachia-infected daughters! 

Woodlouse Wolbachia have spread around the world by manipulating the family lives of their hosts. Wolbachia genes have been detected in Common Woodlice near Rochester, NY. I would be shocked if transgendered Pill Bugs are not thriving here in the Lehigh Valley. For many insects, Wolbachia infections are a win-win situation. The bacteria provide genes that help their hosts manufacture essential nutrients in exchange for a comfy place to live. Nobody knows how Wolbachia affect the health and welfare of woodlice, other than increasing the number of females in the population. 

Woodlice depend on helpful bacteria to digest their food. They use soil microbes to break down the fibers in decomposing plants. This habit allows woodlice to rival earthworms as effective soil improvers. While they love to graze on algae and lichen as well as rotting vegetation, they will occasionally consume live plants. 

Woodlice can become a nuisance in some settings, especially when there is too much moisture around. Some gardeners have become frustrated by the perceived misdeeds of woodlice. Most of the time, the damage was already done.  The plants had started to decompose before the woodlice arrived on the scene. Blaming woodlice for killing healthy garden plants is about as helpful as maligning vultures for apprehending sprightly zebras on the run. 

Some gardeners will never be convinced that woodlice are beneficial creatures.  Folks who become so easily disgruntled with nature are probably not spider keepers. However, they should know they have a friend in the Woodlouse Spider. Also imported from Europe, this spider specializes in woodlice and is apparently common in the Lehigh Valley. I will be keeping an eye out for them.  Meanwhile, a Californian study found that Common Woodlice will feast on a particular type of stink bug eggs. I got really excited about this, until it occurred to me that they don’t seem to have had much of an impact on our   Stink bugs lay their eggs up in trees while the roly-polies keep their antennae to the ground.

Woodlice are one of the few “bugs” that children will encounter without having been taught to be frightened of them. The other day, I was taking pictures of the woodlice in my garden and picked up a few to see if they would curl up into a little ball. I think everybody should try it at least once.

This work by Marten Edwards is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License.

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jennifer July 31, 2012 at 01:38 PM
Very interesting article!
Sunday July 31, 2012 at 01:51 PM
Ahhhhhh yes - pill bugs! I remember playing with them when I was a kid! Incidentally, (a bit off topic-sorry) yesterday was the second time this summer I spotted a bright green stink bug. I once read that the green one's are common down in Florida. Great...now we have them here, too! It was found on my rose bush leaf. The young rose bush is a bit wilted and looks stressed (even though I have been watering it regularly). Sorry, I hate those critters and just had to vent. :( P.S. - Marten - What an abundant year for insects, huh? lol
slyfox July 31, 2012 at 02:52 PM
Who woulda thunk it? Woodlice as a pet. Cheaper than others, I'd imagine. Very informative article. Where DO you come up with these? :o)
Michael Powell September 19, 2012 at 01:17 PM
Nice article, Marten. I am going to guess that there is a fun connection story to the genus name Armadillidum and the armadillo, even if it is just because one reminded the name giver of the other.
Michael Powell September 19, 2012 at 01:26 PM
What we need is a Woodlouse Wolbachia that inclines its host to become arboreal and favor borwn marmorated stink bug eggs. ;)


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