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Crustaceans Among Us

Did you know that you most likely have a crustacean in your backyard? It’s true! You’ve probably all heard of the roly poly bug, sowbugs, or pill-bugs.

This content was originally published by the Longmont Observer and is licensed under a Creative Commons license.

Did you know that you most likely have a crustacean in your backyard? It’s true! You’ve probably all heard of the roly poly bug, sowbugs, or pill-bugs. In actuality, they aren’t bugs at all, but crustaceans most closely related to shrimp and crayfish!

There are over 4,000 species of roly polies worldwide, and they are the only crustacean that lives on land. Their scientific name is Armadillidium vulgare, and I have to say that they kind of remind me of armadillos. Armadillididae is a family of wood lice. They are not native to America, but were introduced from Europe, most likely with lumber. The common name, roly poly, refers to the animal’s ability to roll into a ball when disturbed.

Roly polies are in the isopod family of crustaceans. Isopod means “same pod” or “same foot.” Roly polies have seven legs that are similar in size and shape. They have three main segments to their bodies: head, thorax, and abdomen. They have simple eyes and prominent antennae. Roly polies also have abdominal appendages toward the rear called uropods that assist in locomotion and water uptake. In shrimp and crayfish, the uropods form the tail fan. The roly poly uses gill-like appendages to breathe through. Although they need moisture to survive, they cannot survive underwater.

The roly poly is about 0.7 inches in length when not rolled up. Most range in color from gray to brown, but sometimes you can find a roly poly that is bright blue or purple. These blue bugs are actually sick with a retrovirus. The retrovirus is not harmful to humans. The bright blue or purple color comes from crystals that form beneath the roly poly’s exoskeleton. The exoskeleton, also called a cuticle, is hard and is made from chitin. It is made up of overlapping plates.

(By No machine-readable author provided. Folini assumed (based on copyright claims). - No machine-readable source provided. Own work assumed (based on copyright claims)., CC BY 2.5, https://commons.wikimedia.org/w/index.php?curid=789619)

The roly poly bug has several interesting adaptations. One of the more obvious adaptations is the ability of the roly poly bug to roll itself into a ball. This is also known as conglobation. They share this feature with armadillos. Stimuli, such as vibrations or pressure, may trigger the behavior. The behavior is a defense against predators.

The roly poly also releases a foul-smelling odor. The behavior may also help protect against moisture loss from the body. The roly poly drinks water with its mouth but is also capable of taking water up through capillary action with their uropods (those appendages in the rear of the animal). Roly polies do not urinate.

They are capable of tolerating high amounts of ammonia gas, a byproduct of urea production. The gas simply diffuses out of their exoskeletons. The blood of roly polies is blue due to a compound called hemocyanin. Due to their ability to tolerate heavy metals, roly polies can live in contaminated soil where other animals can’t survive. Roly polies are capable of absorbing moisture through their exoskeletons when ambient humidity is greater than 87%.

The roly poly can be found in cool, dark places that are moist. They are cold-blooded and react very strongly to light, temperature, and humidity. If they are unable to get out of the sun, they will die. Because they are so sensitive to environmental changes, they can be used as biological indicators.

The roly poly can be found in decaying matter and under rocks or other debris. The roly poly eats primarily decaying plant and animal matter and wood fibers. However, they will also eat very young plants leading to them being considered agricultural pests in some areas. However, they also eat the eggs of stink bugs which damage plants, so roly polies act as a natural control for stink bugs.

Roly polies return nutrients from digested material back to the soil. However, when they defecate, they lose copper, an essential nutrient. Because of this, they will eat their own feces (called coprophagy). They are preyed upon by frogs, toads, newts, spiders, and small mammals.

(By Franco Folini - San Francisco, California, CC BY 2.5, https://commons.wikimedia.org/w/index.php?curid=789616)

Males are not needed for reproduction because the females can reproduce through a process called parthenogenesis. There is a bacteria that can turn male roly polies into females. Females will form eggs, then deposit them in a brood pouch. The plates of the exoskeleton overlap and form a special pouch on the underside of the roly poly called a marsupium. Each pouch can hold up to 50 eggs. The average brood consists of about two dozen eggs. Roly polies can have two to three broods per year.

The eggs will hatch in about two months and the babies will stay in the brood pouch for several days before venturing out on their own. Baby roly polies look just like miniature adults but don’t have all their legs and are white. The babies only have six pairs of legs. They will get their seventh pair of legs after their first molt. Juveniles will molt in two sections with the back half of the roly poly molting first. The front half sloughs off several days later. This can create a roly poly that is two different colors. Roly polies will molt between four and five times in their life. The baby roly polies are capable of rolling up just like the adults. Roly polies live between two and five years.

The next time you are in your yard, turn over a rock and look for roly polies. They are fascinating creatures!