Bug of the Week

Millipede (Class Diplopoda)


Greetings, BugFans,

The Bug Lady has been seeing a lot of these small “driveway millipedes” on her walks recently. Millipedes (“thousand legs”) are not insects, of course, but qualify for our attention under the more catholic usage of the word “bug.” Like insects, they are Invertebrates, Arthropods (“jointed legs”); within the Arthropods, they are in the Class Diplopoda (“double legs”). They are in THE most ancient group of terrestrial arthropods still living today, going back more than 400 million years. Cold-blooded, they wait for an invitation from the spring sun before emerging.

The first question about millipedes is “Do they?” The answer, boys and girls, is “No, they don’t.” Millipedes do have two pairs of legs on every abdominal segment (one pair on each side) and a single leg on each side of each thoracic segment. Please do not ask the Bug Lady how to tell a millipede’s thorax from its abdomen – oh wait – by counting the legs on them…. About 30 segments of an adult millipede are leg-bearing. Do the math. (A minority opinion offered by The Handy Bug Answer Book says that each segment does, indeed, have only a single leg on each side, but because a hard shield covers every two segments, it just looks like there are two legs on each side on each segment.). Sobering thought – the longest millipeds in the US live in the Southwest and can grow to be 10 inches long. Lots-o-legs!

A small, 'driveway millipede.'
A small, “driveway millipede.”

When you’re finished doing millipede math, watch a millipede move. Millipedes invented “The Wave;” their legs raise and lower in order down the length of their bodies. When a millipede is scared, it can coil up to protect its soft underbelly and legs. Millipedes have stink glands along the side of the body; some species produce a prussic acid/cyanide compound to discourage or even “off” their predators, but a kid would have to eat lots and lots of them to get sick.

Millipedes are scavengers; they have chewing mouthparts and eat dead stuff (mainly plant material) that they find on the ground. In wet weather, they may chow down on the roots of living plants. Because their exoskeletons include lots of calcium, millipedes are more numerous where soils have high calcium concentrations. The tough exoskeleton allows them to push their way through the soil by brute force, rather than eating their way through like earthworms.

This millipede grew up to be 2 inches long.
This millipede grew up to be 2 inches long.

Millipede eggs are laid in damp ground; millipede babies have just a few segments and three pairs of legs, and they get more of each as they molt. The females of some species take care of their eggs until they hatch.

Centipedes have one leg on each side of each body segment. Centipedes’ legs tend to be longer and they wriggle when they travel because they are moving the legs on one side and then on the other. They are carnivores that stun their prey with venom delivered through the front legs, and they can deliver a painful bite to humans. The next time a House Centipede appears in the Bug Lady’s bath tub, she will photograph it for comparison with the millipede. Unless the centipede was eaten by the snake that is living in the wall behind the bathtub, in which case the Bug Lady will photograph the snake.

The Bug Lady