Millipedes

Millipedes are a group of arthropods^[1] that are characterized by having two pairs of jointed legs on most body segments; they are known scientifically as the class Diplopoda, the name derived from this feature.

Each double-legged segment is a result of two single segments fused together. Most millipedes have very elongated cylindrical or flattened bodies with more than 20 segments, while pill millipedes are shorter and can roll into a ball. The name “millipede” derives from the Latin for “thousand feet”.

Millipedes are cylindrical or slightly flattened invertebrates. They’re not insects—they’re actually more closely related to lobsters, shrimp, and crayfish. The word “millipede” translates to “a thousand feet”—but while millipedes have many feet, none of them quite have a thousand.

There are 7,000 species of millipede in the world, and 1,400 of these occur in the United States and Canada. The smaller ones are less than an inch in length, but the common spirobolid millipede can grow to more than five inches.

Until August 2020 the most legs ever found had been 750. Most millipedes are slow-moving detritivores, eating decaying leaves and other dead plant matter. Some eat fungi or drink plant fluids, and a small minority are predatory.

Millipedes are generally harmless to humans, although some can become household or garden pests. Millipedes can be unwanted, especially in greenhouses where they can cause severe damage to emergent seedlings.

Most millipedes defend themselves with a variety of chemicals secreted from pores along the body, although the tiny bristle millipedes are covered with tufts of detachable bristles.

Its primary defense mechanism is to curl into a tight coil, thereby protecting its legs and other vital delicate areas on the body behind a hard exoskeleton. Reproduction in most species is carried out by modified male legs called gonopods, which transfer packets of sperm to females. The good news is that millipedes are harmless. They’re arthropods, not insects, and are considered a beneficial organism, not a plant pest.

The bad news is that millipedes can become an indoor nuisance, climbing up walls willy-nilly and just being plain ugly to look at (don’t worry; they don’t bite and they don’t breed indoors). Plus, when they die (they dehydrate within a day or two), you’ve got all those curled-up bodies to sweep out so they can decompose.

So what is the difference between Millipedes and Centipedes? Centipedes are elongated segmented (metameric) creatures with one pair of legs per body segment. All centipedes are venomous and can inflict painful bites, injecting their venom through pincer-like appendages known as forcipules. Despite the name, centipedes can have a varying number of legs, ranging from 30 to 382. Centipedes always have an odd number of pairs of legs; no centipede has exactly 100 legs. Like spiders and scorpions, centipedes are predominantly carnivorous.