It is not harmful to humans but can occur in plague numbers, invading houses, contaminating food and infesting carpet and bedding. Plagues may also destroy seedlings and fruit and vegetable crops.
To discourage predators, the millipede releases a pungent yellowish secretion when disturbed. This may stain skin or clothes and is extremely irritating if rubbed into the eyes.
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. Portuguese millipedes are mostly active at night and are herbivorous. During hot dry weather, they hide in the soil. Rainy weather in spring and particularly autumn stimulates activity.
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<table style="border:1px solid;padding:2px; width:310px;" ><tr><td><a href="https://www.scienceimage.csiro.au/image/4002/"><img src="https://www.scienceimage.csiro.au/images/embed/300_0_BE3787.jpg" width="300" alt="Portugese Millipede" style="margin: 0 0 5px 0; border: 0px;"></a><br/><a href="https://www.scienceimage.csiro.au/image/4002/">Portugese Millipede</a><br />by CSIRO</td></tr></table>