The black Portuguese millipede, Ommatoiulus moreleti, is a native of Portugal and was accidentally introduced to Australia, first appearing in South Australia in 1953. They have since invaded all the southern mainland states.
They are attracted to light and will enter buildings at night, although once inside they do not breed and will eventually die.
While there is no evidence they affect human health, they can occur in plague numbers, and can contaminate food and infest carpet and bedding.
Portuguese millipedes are herbivorous, which means in plague proportions they may also destroy seedlings and fruit and vegetable crops.
When disturbed a millipede may release a pungent and distasteful yellowish secretion which discourages predators, such as birds. Note: the secretion may stain skin or clothes and is extremely irritating if rubbed into the eyes. However as it is composed of organic chemicals called quinones, it quickly breaks down in water.
Mature black Portuguese millipedes are smooth and cylindrical, 20-45 mm long and slate-grey to black in colour. Juveniles are light brown and striped. Juveniles hatch from eggs in the soil and reach maturity in two years.
During hot dry weather they will hide in the soil, however rain in spring and particularly in autumn will stimulate activity and breeding.
Portuguese millipedes are attracted to light. If you are able to do so, turn off any external lights which are close to your house or other buildings and minimise any escape of light by closing curtains and blinds. Use weather-strips on doors as good door seals will also help prevent entry into the building.
While compost is good for gardens, it also allows higher populations of millipedes to breed. If you can, reduce the area covered by organic matter such as compost, leaf litter and mulch as it decreases a source of food and shelter. Don’t forget your gutters.
While some spiders, beetles and scorpions will eat millipedes, they will not significantly reduce numbers.
A smooth vertical or rounded barrier can stop millipedes from entering buildings as they are unable to gain a foothold. The barriers can be fixed to walls, below doorsteps, window ledges and vent bricks (make sure you keep them clean and free of vegetation). A barrier must be continuous with no breaks (unless placed under doorways).
Plate glass, 7.5 cm wide and 4.5 mm thick, can also be fitted around the base of a building.
Chemical barriers can be applied to kill the millipedes before they are able to enter your building.
Please note: Pesticides usually have a limited active life and must be re-applied for ongoing control.
Appropriate chemicals can also be applied to outside walls, paths or garden beds and other areas where millipedes may breed.
Chemicals registered for use against millipedes are available from your local supermarket or hardware store.
Please note: Chemicals must always be used in accordance with the instructions on the label.
A simple light trap can be made with a piece of PVC stormwater pipe or a box with holes in it. Place it at ground level near a low voltage garden light or weather-proof fluorescent light to attract the millipedes at night. If you can, place the trap along an outside wall near where the millipedes are entering.
The pipe or floor of the box is then treated with an appropriate insecticide to kill the millipedes after they enter.
A container with smooth and vertical sides i.e. a yoghurt tub is buried flush with the ground away from the building. Place a low voltage garden light or weather-proof light above or as close to the container as possible. As the millipedes are attracted to the light they will fall into the container and not be able to climb out.
Note: You may need to check the traps daily, depending on numbers.