Suborder: Oniscidea

 

Phylogeny

 

This is an isopod. You might know it as a woodlouse, pillbug, sowbug, doodlebug, or roly-poly. Isopods are crustaceans, which is a group within the Arthropods. Insects, arachnids, and trilobites (sadly extinct) are also arthropods. Most crustaceans, including most species of isopod, live in the ocean--crabs, lobsters, etc. Terrestrial isopods are one of the few land-dwelling crustaceans alongside land crabs. Barnacles (another crustacean) are classified as marine even though many spend a good amount of time out of the water.

There is a lot of scientific controversy, it turns out, regarding the phylogeny of the major arthropod groups.

 

Domain: Eukarya (everything with a nucleus)

Kingdom: Animalia (animals)

Phylum: Arthropoda (animals with jointed legs)

"Subclass:" Crustacea (actually a polyphyletic group)

Class: Malacostraca (most of the familiar crustaceans)

Order: Isopoda (crustaceans with lots of feet that look the same)

Suborder: Oniscidea (terrestrial isopods)

 

You also might remember this picture from the older days of the internet. These are giant marine isopods, but unfortunately the bag of Doritos is a photoshopped addition. The largest giant isopod species typically grows up to 14 inches long, and has been confirmed to 20 inches.

They are really popular in Japan.

 

 

 

Isopods have 7 pairs of legs that all look the same, giving rise to the name iso-pod (equal/identical-foot). All arthropods have a cuticle (exoskeleton) made of chitin, the same glucose-derived polymer that makes up mollusc shells and fish scales. Fungi also have cell walls made of chitin. The cuticle of an isopod is divided into overlapping segments. These segments are called pereonites on the thorax and pleonites on the abdomen. Like insects, isopods breathe through their cuticle. Insects have holes called spiracles to let in air, which are sometimes visible to the naked eye. Isopod spiracles are internal and can't be seen from the outside. Some insects have wax layers on their cuticle to conserve moisture, but isopods don't, so they must live in humid environments to keep from drying out.

 

 

 

Life History

 

You can find wild isopods quite easily by digging in the dirt virtually anywhere. They will be small and grey, usually without distinct patterns. Some species curl their bodies into a tight ball when threatened. This is called conglobating and is patently adorable. They are detritivores, so they live in the soil breaking down organic matter. Isopods have been shown to increase nutrient content and decrease acidity in forest soils. For this reason they have become a common addition to bioactive terraria, where they act as part of the cleanup crew that recycles animal waste, eliminates unwanted fungus, and keeps the soil healthy. They are also used as feeder insects for pet reptiles/amphibians. A booming isopod industry has grown up around this practice. The isopods available for sale online are generally bigger and prettier than the common isopods you'll find outside. They're also expensive, so why would people pay for isopods when they can go outside and collect them for free? Well, some people do use wild isopods, but those who opt to buy them do so for hygiene concerns. Wild isopods can bring in diseases or pests (fungi, bacteria, viruses, nematodes, mites, protozoans, etc.) that could harm the soil biome or any larger animals you plan to keep in your terrarium such as amphibians and reptiles. They could also house plant pathogens that will threaten your terrarium's live plants. Store-bought isopods are raised in clean conditions and should never be exposed to such pathogens. Plus, they are much more fun to look at.

 

My Very Own

 

Species: Porcellio laevis Latreille, 1804

 

Last Fall I bought a culture of isopods off Ebay. I wanted them for a bioactive tank I built for my crested gecko. I'm going to write a full post on that project soon. The isopods I bought are called 'Dairy Cow' for their cute black-and-white pattern. They're large isopods with 2 pairs of antennae and 2 appendages sticking out the back, and they can't roll into a ball. All those features are common to the genera Porcellio and Oniscus, which are known as the sowbugs. Technically any isopod outside of these 2 genera can't correctly be called a sowbug.

 

There is a growing community of people who keep isopods as pets. They breed flashy new types just like any pet trade.

I'm not sure if I consider mine pets, but these suckers are pretty cute.

 

Even if you don't want to keep them as pets, rearing isopods can be a lucrative business. They require very few inputs, very little care, and they sell for high prices. I paid $23 for 15 isopods, which was one of the cheaper rates I was able to find. That comes out to $1.53 per isopod, or $ per pound if we assume the average dairy cow weighs blank pounds.

 

Here is my humble isopod home. It's a small plastic box with holes in the lid for air. I put down a layer of jungle mix terrarium soil (basically just a rich dirt), then the sphagnum moss the isopods came in, then a layer of leaf litter. I tried feeding them bits of raw carrot, which they nibbled on a little, but they seem to prefer the leaf litter. I scooped up leaves from my local forest floor, trying to get ones that looked already half-decomposed to give my buddies a softer meal. I included plenty of magnolia and oak leaves, since those are the ones often touted on isopod care pages. I boiled the leaves in water a few minutes to kill pathogens, waited for them to dry and cool, then added some leaves to the isopod box. You can see the skeletonized leaf veins where the isopods have been eating. I've also been pruning my houseplants and adding the dead leaves to the isopod's food--a wonderful little system. The box holds humidity very well, but I give it a water misting every couple days. Many dedicated isopod keepers use larger glass enclosures decorated with bark and plants, but mine seem to be doing fine in their little box for now.

 

 

 

Reproduction

 

About 2 weeks after my isopods came, I opened up the box to find tiny baby isopods running around the leaf litter! I'm proud (perhaps overly so) to be a successful isopod breeder. There seem to be a multitude of the little guys, and I hope the colony continues to grow. Isopods generally reproduce sexually, though a few are parthenogenic (female give rise to more females without mating). Females lay the eggs into a pouch called a marsupium

How many babies? How long to hatch? Don’t have last body segment or pair of legs at first

The larvae look very similar to adults, with no dramatic metamorphosis. In insect we would call this an Ametabolous life cycle, characteristic of the more primitive insect lineages (silverfish). Contrast this to Holometabolous insects like beetles and butterflies, or Hemimetabolous insects (no pupal stage but still a different appearance) like grasshoppers and true bugs and dragonflies.

 

 

 

Update since adding them to the tank. It's been about 3 months? I don't ever see them crawling on the surface of the leaves, but I go in occasionally and dig through the soil gently to check on them. There seem to be plenty of various sizes, so I think the colony is breeding just fine. I add more dead leaves every now and again, and some orange peel, but they don't seem to go through food very fast.