Onigumo - Onigumo

This spider belongs to the Arthropoda phylum, Arachnidae family, and Araneidae order. It is distributed throughout Japan, the Korean peninsula, and China, and commonly lives in plains to mountainous areas. It is a large spider that spins a typical circular web, with females measuring about 30 mm in body length and males measuring about 20 mm. The front shoulders of the abdomen are angular, and there are leaf-like spots on the back. These spots and body color vary widely depending on the region, and some appear to be different species, but there is no essential difference in form. All webs in this family, including this species, are circular, and they have the unique habit of spinning their webs in the evening and folding them up the next morning, but this does not always happen according to the region, weather conditions, maturity, etc.

The closely related red orb spider A. pinguis is a cold-climate spider found in central Honshu and northward, but commonly lives in Hokkaido. Females are 15-18 mm long, males about 10 mm long. The abdomen is round and large, turns bright red when mature, and has small white spots. The Ishisawa orb spider A. ishisawai is endemic to Japan, found from Hokkaido to Kyushu, and is often found in mountainous areas. Females are 18-20 mm long, males about 8 mm long. The dorsoventral ground color is yellowish brown with two white vertical stripes on both sides. The Koke orb spider A. tartaricus is a beautiful spider with a green abdomen and ambulatory legs except for a reddish brown cephalothorax, and its shape is similar to that of the orb spider. It is often found in rice paddies and occasionally in various places. The mountain white orb spider Neoscona scylla is found throughout Japan, and commonly lives in mountainous areas. The body length of females is 12-15 mm, and that of males is 8-10 mm. The carapace is reddish brown, and the head is dark. The abdomen is brown to black, with complex markings mixed with white. The house orb spider N. nautica is found south of Honshu, and up to Taiwan, where it spins webs under the eaves of houses. It is a small species among the orb spiders, with a body length of 10 mm for females and 6-7 mm for males. Its back is black-gray. The doyo orb spider N. dönitzi is found in Honshu, Shikoku, and Kyushu, and is often found in rice paddies. It is a small species among the orb spiders, with a body length of 9 mm for females and 7 mm for males. It matures twice, in summer and autumn, around the time of the dog days. It is known as a natural enemy of pests of rice paddies.

[Takeo Yaginuma]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

節足動物門クモ形綱真正クモ目コガネグモ科に属するクモ。日本各地および朝鮮半島、中国に分布し、平地から山地に普通に生息する。典型的な円網を張る大形のクモで、体長は雌30ミリメートル、雄20ミリメートルぐらい。腹部の前方の両肩は角張り、背面には葉状の斑紋(はんもん)がある。この斑紋や体色は地域的な変異に富み、別種のような感じのものもあるが、本質的な形態に違いはない。本種を含めて、この仲間の網はすべて円網で、夕方網を張り、翌朝網を畳む特異な習性があるが、地域や気象条件、成熟度などによってかならずしもこのとおりではない。

　近縁種のアカオニグモA. pinguisは本州中部以北に分布する寒地性のクモで、北海道には普通にすむ。体長は雌15～18ミリメートル、雄10ミリメートルぐらい。腹部は丸くて大きく、成熟すると真っ赤になり、小さい白斑(はくはん)をもつ。イシサワオニグモA. ishisawaiは北海道から九州まで分布する日本の固有種で、山地に多い。体長は雌18～20ミリメートル、雄8ミリメートルぐらい。背腹の地色は黄褐色で両側に2本の白い縦条がある。コケオニグモA. tartaricusは、赤褐色の頭胸部以外は腹部も歩脚も緑色の美しいクモで、形はオニグモに似る。水田に多く各地でときどき発見される。ヤマシロオニグモNeoscona scyllaは日本各地に分布し、山地に普通にすむ。体長は雌12～15ミリメートル、雄8～10ミリメートル。背甲は赤褐色で頭部は濃い。腹部は褐色から黒色で、白色を交えた複雑な斑紋がある。イエオニグモN. nauticaは本州以南、台湾まで分布し、人家の軒下などに網を張る。オニグモ類中では小形種で、体長は雌10ミリメートル、雄6～7ミリメートル。背面は黒灰色である。ドヨウオニグモN. dönitziは、本州、四国、九州に分布し、水田に多い。体長は雌9ミリメートル、雄7ミリメートルで、オニグモ類中では小形種。夏と秋の土用のころ2回成熟する。水田の害虫の天敵として知られている。

［八木沼健夫］

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