This invasive millipede has noxious secretions to defend itself and can swarm by the millions. They can appear in such numbers they have even caused train crashes! Would you be able to identify a Portuguese millipede?
Common name: Portuguese millipede, black Portuguese millipede
Scientific name(s): Ommatoiulus moreleti (moreletii in older publications)
Description: Adult Portuguese millipedes have a glossy grey or black cuticle, nearly cylindrical body up to 45 mm long, and pale pinkish-white legs. Adults have two pairs of legs on most segments, and up to 50 segments. They congregate in large swarms, and thrash violently or curl into tight spirals if disturbed. Juveniles are brown with a darker stripe along the middle of the back, and have fewer legs.
Native millipedes do not swarm in such numbers, have fewer segments, and are more likely to have obvious constrictions between body segments, or a flattened cross-section, and are much less likely to be a glossy black. As many native millipedes are threatened by the invasive Portuguese millipede, knowing the difference is important.
Geographic distribution: Originally native to Portugal, and accidentally introduced to South Australia in the 1950s. Now found in all southern states.
Habitat: In Portugal the species seems limited to pine and oak forests, but in Australia it is found in gardens, bushland, grassland, agricultural areas, and anywhere plants and decomposing plant material is available to eat.
The millipedes spend summer hiding in humid areas, emerging in large numbers with autumn rain and cooler temperatures.
They mate after the autumn moult, and lose their genitals after each spring moult. 60 to 250 eggs are laid underground, hatching into a legless pupa-like stage, then moult into a juvenile with only three pairs of legs, gaining more segments and legs with each subsequent moult, and reach adulthood after 2 years.
Pest status: Portuguese millipedes generally emerge to feed at night, damaging seedlings, soft fruit, and tainting crops. Their chemical defenses will permanently stain cloth, carpet, and skin, and irritate eyes.
Portuguese millipedes are attracted to low light at night, and will pile up in large numbers at the bottom of walls, or climb up walls and eaves. They may also enter houses, and will die under furniture or in corners.
In large numbers they have caused serious issues with train services, as the squashed millipedes make the tracks slippery, and interfere with signal mechanisms. At least one train crash in Perth has been blamed on the millipedes.
Treatment: The parasitic nematode Rhabditis necromena, originally a parasite of native millipedes, is available from some suppliers, but reduction in millipede numbers may take months or years to show, especially if more millipedes arrive from adjacent properties or bushland.
Residual insecticides applied in a broad band at the bottom of doorways, walls and windows may keep millipedes away from the house, but control over the entire garden is likely impossible, especially where mulch, compost, and extensive groundcover plants encourage humid conditions.
Smooth or overhanging physical barriers and moats may be attached to the bottom of walls, and light traps constructed from stormwater pipe and low-power yard lights and set at ground level have proved effective when treated with pesticides such as carbaryl.
Because of their chemical defenses, Portuguese millipedes should be swept away with a soft broom rather than squashed.
Daniel Heald, technician and entomologist