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Army of creepy millipedes appear in southwest Japan city earlier than usual

An exterminator commissioned by the Kagoshima Municipal Government spreads an insecticide to eliminate Chamberlinius hualienensis millipedes on Sept. 3, 2021. (Mainichi/Junko Adachi)

KAGOSHIMA -- An enormous army of bugs has appeared in a residential area in this southwest Japan city this summer some two months earlier than the insects normally surface, frightening local residents.

    Causing the commotion is Chamberlinius hualienensis, a type of exotic millipede disliked for its creepy appearance.

    In early September, countless dead brown millipedes -- each about 2 centimeters in length -- were seen around houses in an upland residential area in the city's southern district. They had been exterminated with chemicals. A woman in her 60s who lives nearby said, "I couldn't even lie on the floor in August because of the scary thought there might be millipedes there." A man in his 70s added, "They crept up the wall to the ceiling at night."

    Residents have been trying to prevent the insects from invading houses by scattering insecticides distributed by the city for free and guarding entry points with masking tape with a slippery outer surface, but they are not fail-safe measures. And because millipedes let off gas containing a toxic cyanogen compound when stimulated, residents are discouraged from burning or pour boiling water on them.

    A swarm of Chamberlinius hualienensis millipedes are seen in this photo supplied by the Kagoshima Municipal Government.

    The Chamberlinius hualienensis is native to Taiwan, and adults reach 3 to 4 cm long, slightly larger than Japanese millipedes. Though they do not bite humans or damage agricultural crops, they swarm into buildings at night, and residents say they are "creepy."

    Millipedes become active in around September to December in usual years, but they began to appear around July this year, and the amount of insecticides distributed by the city has already reached twice as much as that supplied last year. In the nearby city of Makurazaki, too, applications for insecticide subsidies have climbed to three to four times the normal level.

    Usually, Taiwanese millipede eggs hatch in soil, and the larvae emerge above ground in May to June, then inhabit the space under the fallen leaves they feed on. The insects are highly reproductive, and there have been cases of as many as 1,000 to 3,000 bugs appearing per square meter. They normally begin to spread in swarms from their breeding grounds in around September before metamorphosing into adults.

    Kaoru Takemura, 71, a prefectural task force member who is knowledgeable about the ecology of Chamberlinius hualienensis, suggests a long spell of rain this year has been a factor in the bugs' early appearance.

    "As there was continuous rain this year, the gaps between fallen leaves were filled with rainwater, making it difficult for the insects to settle there," Takemura said. "Another reason their sightings have increased may be that a lot of dung was left on the leaves, making them unsuitable to feed on, and so they moved at an early stage."

    An abnormal number of Chamberlinius hualienensis millipedes appeared in Japan's southernmost prefecture of Okinawa in 1983, and the bugs surfaced in the Kagoshima Prefecture town of Tokunoshima in 1991. They are believed to have propagated domestically after being carried with items such as pot-grown house plants. They have spread to areas where there are plenty of fallen leaves and few natural enemies such as whip scorpions, and have also been found in neighboring Miyazaki Prefecture, Shizuoka Prefecture in central Japan and the remote Tokyo island of Hachijojima, in addition to Kagoshima Prefecture.

    Millipedes prefer shady and humid places where there are plenty of fallen leaves. The Kagoshima Municipal Government is urging people in affected areas to create an environment that the bugs have difficulties inhabiting, by means such as clearing away grass on banks.

    (Japanese original by Junko Adachi, Kagoshima Bureau)

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