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Thursday, May 26, 2005


Butterfly dragonfly

* Japanese name: Choutonbo
* Scientific name: Rhyothemis fuliginosa
* Description: With huge wings colored a beautiful deep blue, this dragonfly is unmistakable. Its body is fairly short and stout, at 32-41 mm long, while its hind wings are 30-40 mm across. The name "butterfly dragonfly" refers both to the long, wide, colored wings (the hind wings are especially wide), but also to the fluttering way the insect flies.
* Where to find them: From June to August, this magnificent dragonfly can be seen flying over ponds, swamps and paddy fields, from Aomori Prefecture in Honshu to Kagoshima Prefecture in Kyushu. There are also reports of sightings in Hokkaido. It seems that it was once seen in large swarms, but population numbers have fallen and these groupings have become rarer as the animal's habitat has disappeared or been polluted with insecticide. It can, however, sometimes be seen around ponds in the suburbs of towns and cities.
* Food: Other flying insects. Mosquitoes are favored prey, and adults can munch through hundreds a day. For this reason alone it's a shame there aren't more of them.
* Special features: The Butterfly dragonfly is in the Libellulid family, which is the largest of dragonfly families. Wing markings in this family are fairly common, but the Butterfly dragonfly is unusual in the extent of the coverage and the brilliance of the pigment. Why does it have such bright metallic-colored wings? The wing color might be a sexual signal of quality to females, just as a peacock's tail is to a peahen. But the problem with this explanation is that the female Butterfly dragonfly also has pigmented wings. The coloring might then be a badge of recognition, a way of quickly identifying members of the same species. Once a positive identification has been made, a male finding a female will grab her behind her neck in midair, using special claspers on the end of his abdomen. Once she's caught, the female, seemingly on autopilot, swings her abdomen around to engage with the male's genitalia. The male uses a specially adapted penis to scrape out any sperm already inside the female from previous matings and then inseminates his own. This ensures that the next batch of eggs she lays will be fathered by him.

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