Episode 141 – Woodlouse: The Pill Bug is No Bug

“…and today we’re talking about a bug of very many names. But more on that right now.”

You might think that gills are just for ocean dwellers, and you’d be wrong. For the terrestrial woodlouse or roly-poly, using gills is as easy as breathing. But how and why does it have gills? It’s all a part of its unique classification as a crustacean rather than an insect–and it involves staying as damp as possible. But keeping it moist is how this isopod of many names survives here in LDT.

Woodlouse Taxonomy

  • They’re in the subphylum crustacea so they aren’t insects at all!
  • Malacostraca is the largest order of crustaceans and it’s made up of crabs, shrimp, krill, lobsters, and all the major players.
  • The superorder peracarida is made of crustaceans with a brood pouch kind of like a kangaroo.
  • Their order is isopoda, which is made up of all-terrain crusties with seven pairs of legs.
  • The suborder oniscidea is made of woodlice!
  • The family Armadillidiidae curl into balls like armadillos.

Description of the Woodlouse

  • The woodlouse is your typically roly-poly pill bug. 
  • They look like a tiny armadillo with segmented armor plates that go widthwise down the back of their exoskeletons. 
  • The front-most armor segment forms a U-shape out of which their broad heads stick out.
  • Two compound eyes grace either side of the head with two segmented antennas come out of the front center of their heads.
  • Their abdomen forms the back third of their body with the majority of their being being taken up by thorax.
  • Flipping the little cuties over will reveal a writhing mass of face-hugger-esque legs.
  • The European woodlouse can be found in dark grey, brown, and black. In some cases, they have a silver lining around each segment. 

Measure Up!

Welcome to the beloved Measure Up segment. The official listener’s favorite part of the show! The part of the show when we present the animal’s size and dimension in relatable terms through a quiz that’s fun for the whole family. It’s also the part of the show that’s introduced by you when you send in audio of yourself saying, singing, or chittering the words measure up into ldtaxonomy at gmail dot com. We don’t have a Measure Up intro this week. That means, we get to hear from an animal and Carlos has to guess what it is.

  1. Giant hornet wings
  2. Hummingbird wings
  3. Giant dobsonfly wings
  4. A vacuum in the upstairs apartment


  • 18 millimetres (0.71 in)
  • How many pill bugs go into the Beats Pill (not a sponsor)?
  • Hint: The Beats Pill was released in 2012 and it was one of the first products that were developed after Beats split from Monster Cable Products.
  • 11.7 pill bugs. The pill was 7.7 inches (20 cm). 


  • 116 milligrams (0.004 ounces)
  • How many pill bugs could go into the largest Glyptodontinae, an extinct ancestor of the armadillo?
  • Hint: Glyptodontinae is thought to have looked like an armored beaver, and lived in South America before the demise of the species. 
  • 17,241,379 pill bugs. The biggest glyptodont is thought to have been as much as 2,000 kilograms (4409 lbs).

Fast Facts About the Woodlouse

The European woodlouse is common all across Europe, the UK, and the Mediterranean basin. 

Most woodlice aren’t able to withstand dry climates because they lose moisture rapidly through their exoskeletons. However, the European woodlouse can withstand drier areas than their kin, hence their broad range. Still, it prefers coastal areas and soils rich in calcium carbonate.

The woodlouse is so-called because it’s often found in decaying wood and plant material. It loves to munch tasty dead plant matter, algae, and lichens. You might find them more easily on cold days when it prefers to bask in sunlight to warm up. When it’s hot, they stick to the shadows, watching… waiting…

The temperate Mediterranean is ideal because of the pill bugs temperature range. It can die in temps below −2 °C (28 °F) and above 36 °C (97 °F). However, on a cold night, they may go into a dormant state to avoid freezing to death.

They’re docile and non-threatening to humans, which is why they are popular among children. However, keeping pill bugs requires specific environments. Do your research before little Timmy brings these crusties into his room.  

Woodlouse Major Fact: A Louse Out of Water

As we now know, gills aren’t limited to just fish, cephalopods, and other sea creatures. We talked about insects like the damselfly larva having gills, but that’s because it lives underwater for most of its life.

So gills are just for breathing underwater, right?

Wrong! The woodlouse puts an end to that hurtful prejudice and shows us that even landlubbers can have gills too.

Woodlice breathe through gills, even though they live exclusively on land. But then why have gills if you breathe air like a normal person? Well, the woodlouse doesn’t exactly breathe air.

It still finds a way to “breathe underwater.” Its gills are located as small flappy appendages to their top ten legs.

These flaps are almost always covered in a thin layer of water. When oxygen from the air hits this water veil, it gets absorbed into the gills.

That’s why they live in moist areas where there is a lot of water to go around. If they dry up, they actually suffocate like a fish or, more appropriately, a crab.

Some species of woodlice have begun to develop small pores on their bellies that lead to tubes where air can pass through and oxygenate the body called pseudotracheae. They still need to use water to absorb the oxygen, but the tubes are on the inside of the woodlouse so they stay moist longer. Adaptation in action!

Ending: So keep your armor close, protect your vital organs when threatened, and always keep your pseudotrachea moist like the woodlouse here in LDT.