Invasion of the millipedes

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NOT since the threat of the Luftwaffe has such drastic action been necessary. Three villages in north-west Scotland are imposing a wartime-style "blackout" to help repel a new invasion force.

Later this month, thousands of inch-long black millipedes are expected to hatch and wriggle their way into baths, beds and kitchens on the Sandwood Estate on the west Sutherland coast.

Attracted by light, the millipedes will enter houses through tiny cracks and climb up internal walls and across floors and ceilings. The invasion is expected to last until August.

The local council says it cannot help so the estate owner, the John Muir Trust (JMT), has come up with a novel solution. Based on experience in Australia, where homes have suffered similar invasions, residents are being urged to black-out their homes at night so they are less of a target. European black millipedes – tachypodoiulus niger – are most active between one hour after sunset and one hour before dawn.

One resident planning to impose a blackout is postmistress Bridget Graham, who has lived in Balchrick for 37 years.

"I'll try anything," she said. "They could start appearing any time now and everyone is desperate to stop it. They are horrible. They start in April and last year they were still coming in in October."

All the residents tell stories of millipedes swarming across village roads and getting into baths, showers, bedrooms and cupboards. Across from the post-office, holidaymaker Fiona Young, who visits her family in Balchrick every year during the summer, found them crawling over her four-year-old son when she went to wake him in the morning.

Graham said: "It's hard to believe how bad it gets unless you are here and see them. We have tried insect powders. Others constantly wash down their walls but nothing seems to work. We need help but really we have been told we just have to grin and bear it."

Although scientists have been unable to pinpoint the cause, millipede invasions started about four years ago and have been increasing in intensity ever since. The area has always had the calcium-rich soils that millipedes like. They feed on rotting vegetation which is rich in the calcium they need to help form their exo-skeletons.

Millipede experts believe the explosion in numbers could be attributed to a succession of milder, wetter winters which have allowed more eggs to survive to hatching time. A reduction in crofting activity in the area, leading to longer grass for eggs to lay undisturbed, may also have contributed.

Cathel Morrison, the land manager for the conservation trust, said: "We have been taking advice from millipede experts about how best to combat the millipedes from swarming into private homes within our Sandwood property.

"They have told us that there have been big problems with swarming millipedes in other countries in recent years. Experience in Australia has found that blacking out homes has helped deter these nocturnal visitors as millipedes are drawn to light at night.

"The JMT does not advocate the use of toxic chemicals to control these insects and the communities are too spread out to build a low wall around. We will therefore be advising a wartime blackout for residents of Droman, Balchrick and Blairmore this spring. Simple measures such as switching off outside lights, drawing all the curtains and putting draft excluders on the external doors could make all the difference."

The Sandwood Estate, located on a scenic stretch of coastline between Kinlochbervie and Cape Wrath, was acquired by the trust in 1993 to preserve its remote beauty. Around 100 people live in the crofting area in a series of small villages.

Investigations into the outbreaks have been conducted by both Highland Council and Scottish Natural Heritage but they have been unable to offer a clear solution. The council says millipedes are not classed as pests, but are "wild creatures" so it does not have powers to deal with the problem. As they do not bite or sting and do not pass on diseases, they are not a public health issue.

A council spokesperson said: "Although we appreciate the distress this must cause residents in the Sandwood Estate, unfortunately the millipedes are spread over a wide area and there is nothing the local authority can do to assist.

"We have tried applying barrier sprays along window ledges and doors at one property in the area but this had little effect. If the council were to use an insecticide over a large area, we would kill many non-target species, which is not permitted."

The council added that it had discussed the situation with SNH, pesticide suppliers and affected residents. "It has been suggested that if the land was worked and soil turned over, this might expose the millipedes and their eggs thus allowing them to be eaten by predators."

The British Myriapod (centipedes and millipedes) Society said millipede swarms were highly unusual in the UK but there had been recorded episodes in Germany, America and Australia.

However, although one German village had built a low, curved wall around houses to stop millipedes this was not feasible among the scattered crofts on the Sandwood Estate.

BMS secretary Helen Read said: "Imposing a blackout has had some success in Australia so it is worth trying. Hopefully, as the millipede swarm in Sandwood appeared from nowhere it may also eventually disappear of its own accord."

Legs and Co

Tachypodoiulus niger, known variously as the white-legged snake millipede or the black millipede, is a European species occurring in the British Isles, Spain, France, Benelux, Germany, Switzerland, Austria and the Czech Republic. It is especially common on chalky and limestone soils.

The millipedes have a cylindrical, shiny black body, with around 100 pairs of contrasting white legs on around 50 body segments. They live in leaf litter, under bark or in moss, and feed on rotting vegetation. Predators include centipedes and hedgehogs.

Millipedes are most active from one hour after sunset to one hour before sunrise, although in summer they become active in the afternoon. When in need of protection, like many millipedes, tachypodoiulus niger coils itself into a spiral, with its legs on the inside and its head in the centre but it can also flee with sidewinding movements.

Around the world, there are thousands of species of millipedes. Many also emit poisonous liquid secretions or hydrogen cyanide gas through pores along the sides of their bodies as a secondary defence. Some of these substances are caustic and can burn the exo-skeleton of ants and other insect predators, and the skin and eyes of larger predators. As far as humans are concerned, this chemical brew is usually harmless.