Black Portuguese Millipedes

Brief:

The black Portuguese millipede, Ommatoiulus moreletii, is an herbivorous millipede native to Portugal. This species was accidentally introduced into Australia where it has since become an invasive pest.

Adult black Portuguese millipedes are smooth, 20 – 45 millimetres long and coloured from grey to black their bodies are composed of numerous similar segments between a head and a tail end. Each body segment has 2 pairs of legs on each segment, although the first few segments may have only a single pair of legs. Immature specimens are striped and light brown.

Habits

Black  are herbivorous detritivores, which means they obtain nutrients by consuming decomposing plant materials and by doing so, they contribute to decomposition and the nutrient cycles.

Portuguese millipedes hatch from eggs in the soil, and initially have only 3 pairs of legs. They moult as they grow; adding segments and legs, and reach maturity at 2 years. They are mostly active at night and during hot dry weather the millipedes remain hidden in the soil. Rainy weather in spring and particularly autumn stimulates activity, often leading to outbreak numbers with thousands of millipedes on the surface.

Adult males are periodomorphic, alternating between a sexual and a non-sexual form. In their sexual form, they have gonopods (mating legs) in the seventh body segment, which they lose when they moult in spring. They remain in the non-sexual ‘eunuch’ form until their late summer moult.

As a defence mechanism, the millipede secretes a pungent yellowish fluid containing hydrogen cyanide. This stains clothes permanently and irritates eyes.

Habitat

Black Portuguese millipedes are most often seen in moist conditions, which create an abundance of food. Since being introduced to Port Lincoln, South Australia in 1953, the millipede has spread to other parts of South Australia, Victoria, Tasmania, Australian Capital Territory, southern New South Wales, and Western Australia around Perth.

Threats

Lacking natural predators in Australia, the black Portuguese millipede has flourished to ‘plague’ proportions. They have been known to enter residences due to their sheer numbers.

The millipedes were crushed in great numbers crossing the railway tracks at Tallarook, central Victoria in March 2009, causing train cancellations due to the disturbance of signalling equipment. Crushed millipedes were also implicated in a 2013 minor train crash. In the implication it was posited that crushing the insects on the tracks interfered with the train's deceleration.

Prevention

Barriers - both chemical and physical - and light traps are the most practical ways of preventing millipedes from invading houses. At the landscape scale, biological control is probably the only feasible method, but no suitable agents have been found yet. A parasitic nematode has had limited effect. A suitable chemical, applied in a band wide enough to kill millipedes crossing it, can be applied to brick or cement surfaces around the house, and to doorsteps and window ledges. Prepare and apply the chemical according to directions, and reapply as necessary. Physical barriers stop and/or trap millipedes moving towards the house. A smooth, clean, vertical surface is effective, or a moat with overhanging sides. They are also attracted to light, and you can construct a millipede trap out of a length of oblong-section galvanised steel downpipe and a low voltage bulb.

As a defence mechanism, the millipede secretes a pungent yellowish fluid containing hydrogen cyanide. This stains clothes permanently and irritates eyes. Due to this defence it is best for people to sweep them up rather than crushing them.

Others

Photo and information are provided by J. Coelho and WR Gay Pest Control Pty Ltd.

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