Harmful insects' habitat widens with global warming

Harmful insects' habitat widens with global warming

The domestic range of the tiger mosquito, a major carrier of the dengue virus, has expanded as far north as Akita and Iwate prefectures.

Global warming is the apparent cause of the expansion, which comes as the first domestic cases of dengue fever in decades have rattled the nation this year. Up through 1950, tiger mosquitoes were found no higher than the northern Kanto region, but with climate change more and more apparent, they and other hazardous animals have been spotted more widely around the country.

The Environment Ministry has also warned that animals not previously seen in the nation could harm people.

The dengue virus is mainly transmitted by tiger mosquitoes. According to the Tokyo-based National Institute of Infectious Diseases, the northern limit for that insect's range had expanded to Miyagi and Yamagata prefectures by 2000. It has since stretched even further north.

Courtesy of National Institute of Infectious Diseases Tiger mosquito In 1950, the mosquito's northern limit only reached to near the northern borders of Ibaraki, Tochigi and Gunma prefectures.

Its current range almost perfectly overlaps areas that have registered annual average temperatures of 11 C or higher.

In March, the institute and other organisations projected that the mosquito's northern limit would reach Hokkaido unless effective measures to fight climate change are implemented.

"If global warming worsens, the risk of [dengue] infection will increase," said Kyoko Sawabe, chief of the institute's Department of Medical Entomology.

The blue-striped nettle caterpillar, a moth larva about five centimeters long, has also been detected more widely.

Earlier last month, a pest-control worker commissioned by Tokyo's Edogawa Ward found a large number of the caterpillars on the underside of leaves when he disinfected maple trees near the ward office.

They are believed to be native to Southeast Asia. Touching the caterpillar's spines feels like an electric shock, causing it to be called an "electric worm."

Several hundred caterpillars were found during about four hours of the ward's pest-control activities. Every year, the ward receives reports from residents who were stung.

According to the Environment Ministry, the species was spotted in Kagoshima Prefecture in the early 1900s. Its range expanded to the Kinki region in the 1970s to '80s and to the Kanto region in the 2000s.

"Its range has moved northward partly due to rising temperatures in winter," a ministry official said.

Another creature expanding its range is the redback spider indigenous to Australia, the bite of which can cause acute pain and vomiting. There have even been fatalities overseas.

According to the National Institute for Environmental Studies in Tsukuba, Ibaraki Prefecture, the spider's range has expanded to 35 prefectures since it was found in Osaka Prefecture in 1995. In recent years, the species has also been discovered in the Tohoku and Hokuriku regions.

The spider is suited to an environment with temperatures of 15 C and higher.

"In the Tohoku region, [redback spiders] are believed to live in places such as sewer pipes through which warm drainage flows," said Koichi Goka, a senior researcher at the institute. "The number of places they can live has increased due to rising temperatures."

A private study group called the Yamabiru (land leech) Kenkyu-kai has found that 34 prefectures have received reports of people being bitten by the leeches, which feed on the blood of humans and wild animals.

Up through 1980, only four prefectures, all in the Kanto region, had received reports of such bites.

The Tokyo-based group says the growing number of deer and boar has helped transport the leeches around the nation.

Some experts attribute the increase in deer to reduced snowfall, which allows them to survive the winter more easily. Group head Kazu Tanishige said, "We've received reports of injuries and damage caused by the leeches in winter that weren't seen before.

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