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Millipedes

Also known as Diplopoda, Greenhouse millipede (Oxidus gracilis), Spotted snake millipede (Blaniulus guttulatus)

Beneficial or harmlessDepends
The greenhouse millipede (Oxidus gracilis), a flat-backed species common in warm regions Photo: Australocetus · CC BY-SA 4.0

In short

Millipedes are slow, many-legged scavengers of decaying plant material and are part of a healthy soil. Their mouthparts are weak, so they rarely start damage, but in large numbers they may nibble seedlings, soft growth and fruit lying on the soil, and they enlarge wounds started by slugs.

How it looks

Long, segmented bodies with two pairs of short legs on most segments. Many are rounded and dark brown, up to about 4 cm long; the spotted snake millipede is slender, creamy white, up to 20 mm long, with a row of reddish spots along the sides; flat-backed millipedes have flattened keels on each segment. They move slowly and coil up or stay still when disturbed.

Signs

Usually none. Where numbers are high: grazed seedlings and soft shoots, and holes enlarged in bulbs, tubers, root vegetables and strawberries already damaged by slugs or disease. They may wander indoors in large numbers after wet weather.

What favours it

Moist soils high in organic matter, thick mulch, compost and overripe fruit.

Prevention

  • Reduce slug damage, since millipedes mostly exploit existing wounds.
  • Keep seedlings growing strongly and raise strawberry fruits off the soil.
  • Keep mulch thin enough to dry at the surface and clear rotting fruit and debris.

Treatment

Start with the first step and move down only if the problem persists.

  1. Usually none: they are detritivores and should not be controlled.
  2. Indoors, sweep or vacuum strays and reduce damp hiding places near doors.
  3. Pitfall traps or removing debris can lower local numbers around seed beds.
  4. Insecticide barrier treatments are rarely warranted; if used, follow the product label.

Pros and cons

Pros

  • Recycle nutrients by feeding on decaying organic matter and associated fungi.
  • Food for birds, frogs, toads, hedgehogs and ground beetles.

Cons

  • Can graze seedlings and very soft growth, and enlarge existing damage in bulbs, tubers and fruit.
  • Can invade homes in large numbers after wet weather.

Look-alikes

Centipedes
Centipedes have one pair of legs per segment, a flatter body, long antennae and run fast; millipedes move slowly.
Wireworms
Stiff, shiny beetle larvae with only three pairs of legs near the head.
Woodlice
Only seven pairs of legs and an oval, plated body.

Where you find it

Seedlings, strawberries, bulbs, potato tubers and root vegetables, usually only where tissue is already damaged.

Sources

  1. Millipedes — RHS
  2. Millipedes, centipedes, sowbugs and pillbugs — Colorado State University Agricultural Biology
  3. Millipedes, Centipedes, Sowbugs and Pillbugs (IG093) — UF/IFAS

Written in our own words from these sources. Check a product label before using any treatment.