Are Millipedes Poisonous? Defensive Chemicals and Real Risk

Can millipedes hurt you?

Millipedes are slow, gentle animals that eat decaying plant matter. Their jaws are designed for chewing leaf litter and soft wood, they have no fangs, and they have no venom glands. They do not bite or sting people.

Their protection is chemical. Along the sides of the body most millipedes have tiny openings called ozopores, which lead to defensive glands. When a millipede is grabbed, squeezed or attacked, these glands release a fluid that smells bad, tastes worse and can irritate or burn the skin of small predators.

For a person, the main effects of handling a millipede are:

• A strong smell on the hands
• Yellow, brown or purplish staining of the skin that may take days to fade
• Itching, burning or redness, mostly with large tropical species
• Irritation and possible damage if the fluid reaches the eyes

So the accurate answer is that millipedes are mildly toxic to touch, not dangerous animals. They are not “venomous”, a word for animals that inject toxins through a bite or sting, but they are chemically defended.

What chemicals do millipedes release?

Scientists have identified many kinds of defensive compounds in millipedes. The main groups are:

Benzoquinones are reactive chemicals that cause the typical brown staining. The giant African millipede, for example, releases toluquinone and a related quinone.

Flat-backed millipedes store a harmless precursor chemical and an enzyme in separate compartments. When the millipede is disturbed, the two mix and release a small puff of hydrogen cyanide together with benzaldehyde, which gives off a smell of bitter almonds. The yellow-spotted millipede (Harpaphe haydeniana) of the Pacific Northwest, shown above, is a well-known example and is sometimes called the almond-scented or cyanide millipede.

Is millipede cyanide dangerous to people?

The quantity of cyanide one millipede produces is tiny. It is enough to drive off an ant, beetle or small bird, but far too little to harm a person outdoors. Some millipedes are even brightly colored, a warning to predators that they are distasteful, as in the yellow-spotted millipede and the glowing Motyxia millipedes of California, which also produce cyanide.

That said, the fluids should be treated with respect. Medical reports describe “millipede burns”, areas of brown or purple discoloration, blistering or irritation after skin contact with large tropical species. If secretions get into the eyes they can cause serious irritation, so anyone with eye exposure should seek medical help promptly.

The simplest precaution is to watch millipedes without handling them, especially large ones, and keep them away from the face. Children and pets are the most likely to pick up or mouth a millipede.

How do millipedes protect themselves?

Chemicals are only part of a millipede’s defenses. Because millipedes are slow and cannot fight back, they combine several tactics:

Curling up. Most millipedes coil into a tight flat spiral when disturbed, with the head in the center and the soft legs hidden. Pill millipedes roll into a perfect ball, like a woodlouse. In both cases only the hard, calcified outer rings are exposed.

Hard armor. Most millipede body rings are reinforced with calcium salts, making them difficult for small predators to crush.

Bristles. The tiny bristle millipedes have no chemical glands. Instead they are covered in tufts of hooked bristles that come off and entangle the legs and jaws of attacking ants.

Warning colors. A few species, including some bright yellow, orange or red forms, advertise their unpleasant chemistry to predators.

Which animals use millipede chemicals?

Some animals have learned to cope with, or even make use of, millipede defenses. Meerkats and coatis roll millipedes along the ground to wipe off the secretions before eating them. A group of assassin bugs specializes in hunting millipedes, and some poison dart frogs may gain chemicals for their own defense from the prey they eat.

The most remarkable users are primates. Lemurs in Madagascar and capuchin monkeys in South America have been seen gently biting millipedes to make them release their fluid and then rubbing it into their fur. This behavior, called anointing, is thought to protect against mosquitoes and other biting insects, as benzoquinones are known insect repellents. The millipedes are often released alive afterward.

Millipedes vs centipedes: which is dangerous?

People often confuse the two. Centipedes are fast predators with a pair of venomous claws behind the head, and large species can give a painful bite. Millipedes are slow plant-debris eaters with no venom at all. If the animal is quick, flattened and has one pair of long legs per segment, it is a centipede; if it is slow, rounded and has short legs underneath, two pairs per segment, it is a millipede. See centipede vs millipede and How many legs does a millipede have? for more.