Millipedes on a tree stump with fungi, Schenley Park, 28 June 2026 (photo by Kate St. John)

30 June 2026

Last Sunday in Schenley Park we discovered that right now it’s Millipede Mating Season in Pittsburgh. Millipede mating habits are so fascinating that I had to look into it.

First off, millipedes are not insects; they have a lot more than six legs. Their class Diplopoda contains 13,000 species, all of which have two pairs of jointed legs per body segment. The number of body segments varies a lot from short pill millipedes to Eumillipes persephone which can have over 1,300 legs.

Their name literally means “thousand feet” but most millipedes have far fewer. Count the body segments (but not the head) and multiply by 4. The ones in my photos have less than 100 legs.

They appear to be greenhouse millipedes (Oxidus gracilis) which were originally from Asia and are now invasive in North America. The name “greenhouse” comes from the fact that they thrive in greenhouses where they become pests. They can also live in cool moist woods where they feed on decaying plant matter.

When millipedes mate, copulation happens in the first seven segments but courtship involves all the segments. First they have to find each other, complicated by the fact that greenhouse millipedes cannot see — they don’t even have eyes. The males emit sex pheromones to attract the females.

After they find each other by scent and touch, the male walks on her back to stimulate her with rhythmic movements of his legs. It also calms her so she won’t reject him or curl up in a defensive posture.

Here are a male and female in a mating embrace on the tufa bridge over Phipps Run. Once we started looking we found many millipedes in the tufa crevices.

Mating millipedes in Schenley Park, 29 June 2026 (photo by Kate St. John)

In this marked up photo you can see which one is the male — he’s shorter. There’s also a second couple nearby.

Mating millipedes markup — actually two couples, Schenley, 29 June 2026 (photo by Kate St. John)

The male has to cling to the female for the next step.

In most millipedes, including [study subject] Pseudopolydesmus, the male’s testes are located in the body starting behind his second pair of legs. But his gonopods, the specialized pair of legs used to insert sperm into the female, are way back on his legs of the seventh body ring. “He has to ejaculate and then dig his seventh-ring gonopods into that ejaculate,” she explains. “It’s a blue-ish liquid.”

Once the male has gotten his gonopods covered in blue ejaculate, he’s ready to insert them into a female’s vulvae. “She has two openings, one on each side between her second pair of legs,” says Sierwald. …

After mating, the female’s vulvae get sealed up with a gooey secretion, trapping the sperm inside. Later, when she lays her eggs, they get coated with the stored sperm on their way out of her body.

The females lay 40-50 eggs in cool, dark, moist soil. The tufa bridge looks like the perfect place.

Two millipede couples mating on the tufa bridge in Schenley Park, 29 June 2026 (photo by Kate St. John)

If you’re curious about Millipede Mating Season check out the tufa bridges in Schenley Park or read more here Field Museum, Feb 2020: Scientists finally figure out how millipedes actually do it.

Will this week’s humid heat wave shut down their activity? Or will their tropical origin make them happy that it’s hot?