A CURIOUS GARDEN: Pill Bugs

A Roly Poly gnawing at a strawberry.

A Roly Poly gnawing at a strawberry.

Contributed by Nancee Foglesong, Master Composter.

Did you know that Roly Polies are not insects, but crustaceans? These creatures, more formally known as pill bugs (Armadillidiidae), have a tendency to roam into our compost bins. Many composters are concerned about transferring these little creatures from their cured compost into their garden. Do Pill Bugs pose a threat to plants?

The Quick Answer: Pill bugs do not normally eat live plant material. Like earthworms, pill bugs seek out moist, dark habitats—making a compost bin an ideal home. Their diet in the compost pile is identical to their diet in natural surroundings, consisting largely of rotting wood and decomposing plant and animal matter. (Occasionally, they may eat a fellow live pill bug, if other food sources are scarce.) Unlike worms, pill bugs have mandibles consisting of 2 jaws to chew up their food. The food passes through their digestive system, releasing some moisture and nutrients before exiting through the anus as droppings.The droppings now have more easily digestible nutrients, and are often consumed by the pill bug. Like the beloved earthworm, pill bugs are also recyclers that create nutrient-rich soil, and do not technically need to be removed from finished compost before it is used in the garden.  However, like other creatures, opportunistic pill bugs may eat live plants. Ultimately, if pill bugs are found in a compost pile or worm bin, it is a sign of a healthy compost environment.

As I said, that was the quick answer. I am rarely satisfied with the simple answer. I wanted to know why some gardeners were having problems with pill bugs in their garden. What was I missing?  After searching through quite a few books, and online, I only found one reference to pill bugs eating live plants. Evidently, they will eat through a strawberry patch if given the opportunity. But all other reference materials indicated that these little creatures are fellow soil recyclers. In fact, several references indicated that if pill bugs are found in a compost pile or worm bin, it is a sign of a healthy compost environment.

The only advice I found citing pill bugs as problematic in the garden was in Loren Nancarrow’s book, aptly named The Worm Book, written with Janet Hogan Taylor. He suggests that while transferring cured compost to the garden, gardeners “hand-pick [pill bugs] out. Don’t worry—they won’t bite.” And they don’t carry any diseases.

Seeing is Believing: 

But once again, I wasn’t quite satisfied with this information, especially after I went out one morning to check on my two raised beds of strawberries. It was overcast and still a bit dark; I had watered the beds the night before, so the soil and plants were still moist. And guess what I found: pill bugs busily munching on my strawberry plants.  Big and small, these little animals were apparently enjoying an early morning meal. Before I disturbed them, I wondered if the other bed of strawberries had been attacked as well. Not one pill bug was visible. I went back to the first bed, and watched as they chewed up another leaf. What was different between these two beds? Why was only one bed of strawberries overrun with pill bugs? And why hadn’t I noticed this before? It was then that I realized that I had spread cured vermicompost on only one bed of strawberries, the one with all of the pill bugs. I had been the one to put them in there—they had hitched a ride in the freshly applied compost. In my worm bin, they had been quite satisfied with the organic matter I delivered to them in the form of kitchen scraps and shredded paper. Now, they were happily eating my plants.

Another fact became clear when I tried to capture a few of the little isopods. As soon as they sensed the disturbance of my hand moving the leaves and dirt, they rolled up into balls, scurried under leaves, or dived into the soil. I had a hard time ‘hand picking’ them out! I finally resorted to scooping out a small handful of soil to capture a few specimens, dumping them into a bug keeper. I wanted pictures of these little neighbors. I managed to get a range of sizes, from about 1/8” to about ½”. I especially wanted pictures of their undersides to inspect. Once captured digitally, I released the pill bugs back into a less-tantalizing area of my garden, hoping they wouldn’t find a way back into my strawberry patch.

Semi-Final Answer: Unfortunately, the advice remains the same; if you don’t want the pill bugs in your garden, hand pick or gently screen them out while the compost is curing.  Generally, pill bugs are good macro-organisms to have in the garden, as they work alongside other soil recyclers. If you don’t have the time to screen your compost for the critters, perhaps you have a neighborhood child or teen that would be willing to help. My 4-year-old neighbor has turned out to be very interested in ‘bugs’, and happily helps me with small chores. Meanwhile, I will continue looking for more ways to deal with pill bugs already residing in the garden.

pil bugPill Bugs are Not Insects:

Although these fascinating creatures are often called ‘bugs’, pill bugs are not insects.  Pill bugs and sow bugs are different species, but both belong to the phylum Arthropoda, and class Malacostraca. They are part of the family of Armadillidiidae, soil crustaceans that are related to crabs, lobsters, shrimp, and barnacles.  This relationship is evident when examined up close. When magnified, (I turned one over and took a picture, then zoomed in to see more clearly) the tail end of this soil arthropod is remarkably similar to the tail end of a lobster. The main difference between pill bugs and sow bugs is the pill bugs’ ability to roll into a ball for defense. Because sow bugs (and other members of the woodlice family) cannot do this, you can differentiate between the two by gently touching the soil crustacean to see if it rolls up.  If it does, it’s a pill bug.

Pill bugs are Isopods, having legs of the same length. Their ‘body armor’ ranges in color from light grey to brown to purple. If you find a bright blue pill bug, it likely has a virus (not transferable to humans). They have three main body parts, the head, the thorax, and the abdomen.

The head has a mouth with mandibles, two strong jaws to chew its food, creating more surfaces for beneficial bacteria and fungus to grow.  The two eyes are compound eyes, made up of 15 to 20 small eyes, each looking in a slightly different direction. The antennae are two sets of feelers, one set larger and longer, that taps on the ground to find food and mates. This set of antennae can fold up into a hollow in the head when the pill bug rolls into its spherical defensive position. No purpose has yet been discovered for the second set of antennae.

The thorax is the portion of the body that is covered by the seven segments of the exoskeleton. The seven pairs of legs are attached to the seven segments. Their legs are jointed and have bristles; the part of the lower joint often rests on the ground and the bristles give them better traction. In a lesser-known ecological role, pill bugs are important carriers of microbial life.  As they move about foraging and eating, microorganisms carried on the pill bug’s body are dispersed as the host travels.

The abdomen is the last portion of the body where the europods are found. The europods are two small, tail-like stalks that assist in moisture uptake so vital to the pill bug. Pill bugs have no lungs, but a feature quite similar to gills to breathe and to absorb additional moisture. As moisture is absorbed, the gills separate out the oxygen to be used in the blood stream.While often recognized for the nutrients they excrete, an important mineral found inside pill bugs is copper. Copper carries oxygen throughout the circulatory system of the pill bug. Just as the mineral iron carries oxygen through the human system, making our blood red, the copper in a pill bug’s system makes its blood blue.

Three Stages of Life     The pill bug goes through three stages of life: first as an egg, then a manca, and finally, an adult. After mating, the female lays a brood of eggs (which may be up to 250 in count). Many species of woodlice carry the eggs in fluid-filled pouches under the portion of their body known as the abdomen. The eggs may hatch within two to three months, and the nymphs may stay in the pouch a little longer. At this point, the nymphs have only six pairs of legs. Once they emerge from the pouch, they are known as mancae. Within 24 hours of leaving the brood pouch, the manca will begin to molt, shedding the first softer shell to fit the larger underbody. It is at this point, that it adds the seventh pair of legs, and is designated an adult pill bug. In appearance, this new adult will look identical to the more mature adults, just much smaller. As it grows over its three- to four-year lifetime, it will molt up to 12 more times. During the molting process, only half of the shell, the exoskeleton, will be shed, leaving this soil crustacean vulnerable to predators. As the exposed portion of its white body grows a new shell, the 2nd half of the body will shed as well. During this time, it does not eat, nor can it roll up in defense. It also has no ability to retain the vital moisture needed for survival.

Soil Recyclers      These soil crustaceans are natural recyclers, chewing up the larger pieces of dead plant and animal material in their environment. They often come out at night to find food and to take in moisture. Their droppings become part of the rich nutrient mix so vital for plant growth and vitality. As stated in Teaming with Microbes, by Jeff Lowenfels and Wayne Lewis, “As these arthropods go about their business, they mix and aerate soil; their waste products also add organic matter.” As we gardeners and composters become more acquainted with the life forms in our soil and bins, we truly can begin to see an extended web of life, one where all life forms are interdependent. Remove one strand, and the entire web changes.

About my Bibliography: You will find that I use a mixture of adult reference books, as well as children’s books. I have found that children’s books are often a source of solid and easily attainable information. Check it out!  I also use websites that are usually linked to universities or professional organizations. My criteria for research data is that all facts must agree in 2 or more reference materials; if not, I will state that there are conflicting facts.

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s