Portuguese millipedes were first detected in Western Australia around Roleystone in 1986. Unfortunately this introduced pest has now become established throughout the metropolitan region and other areas in the southwest. They normally live outdoors where they feed on leaf litter, damp and decaying wood, fungus and vegetable matter.
Portuguese millipedes become highly active usually after the first rains. They are not harmful to animals or humans, but they can be a significant domestic nuisance when they invade homes and gardens in large numbers usually in early autumn. They are one of the few millipede species that are attracted to lights at night, and this is presumably why they invade homes. Different properties will be affected by these millipedes to greater or lesser degrees depending on varying situations.
As they are not harmful to public health the City does not have Local Laws requiring property owners to undertake treatment. Given their widespread distribution across the state it is also not practicable for the City to treat for these pests on City owned land. This is due to a number of factors including;
- Any chemical treatment will only have effectiveness for a limited time.
- It would take considerable time to treat the entire City of Swan given its large size.
- It would be difficult to time the treatment to coincide with the first rains when the millipedes are most active given the time that would be required to undertake a treatment and the usual weather forecasts.
- As these millipedes generally only become active after the first rains it is difficult to determine if millipedes are present beforehand. Therefore undertaking a treatment program would likely involve areas where millipedes are not present having to be treated.
- The City would only be able to treat land which it owns or has control over.
- Land which was private property, or in other councils or State Government owned would not be able to be treated by the City. Therefore millipede populations on these lands would remain untreated and would soon be able to recolonise City controlled land.
- Chemical treatment may have an adverse effect on other native fauna e.g. other insects would be also killed thereby affecting the food chain of larger animals.
- Treatment would be required to be undertaken on an ongoing basis.
- The cost of treatment would be severely high.
- The millipede problem whilst severe initially, usually dissipates quickly as winter approaches.
- This is a multijurisdictional problem and needs to be addressed as a state issue and not individual Councils. We are not aware of any other Council currently undertaking treatment for Portuguese millipedes.
There are steps individual properties can take to reduce the effect of these pests. These include turning off external lights and minimising the escape of light from inside through the use of curtains and blinds, removing leaf litter from garden beds, installing physical barriers, using chemical barriers or using light traps to draw and capture the millipedes away from the residence.
Light traps offer a relatively simple, cheap and chemical free option to property owners. They can be as simple as burying a bucket at ground level away from the residence with a waterproof light suspended above it. The millipedes are drawn to the light and captured in the bucket. We understand there is a commercial product along this theme called ‘millipede catcher’ and a web search should provide a list of stockists and information. Please note the City has not trialled this product and this is not an endorsement of it but rather provided as an example of the principals of a light trap in action.
More info on millipedes and these techniques is detailed in the attached Portuguese millipede fact sheet(PDF, 156KB) from the Department of Agriculture.