Hiroshi Abé and Hinako Okuhara

Females' web-building characteristics of Achaearanea japonica (Arachnida: Araneae).

Number: 269, Pages: 1 - 12

Achaearanea japonica is one of the quite common spiders throughout Japan. To understand the biology and ecology of A. japonica , we examined the females' web-building characteristics in relating to body size, web volume, and web height above the ground level. The 79 webs of sub-adult and adult females were examined from May to September in 2010 at a hedge of Photinia glabra in a ground of Nihon University , Kanagawa, Japan. As a result of the investigation, adult females built a larger web than sub-adult females, and the body sizes of adult females were significantly larger than sub-adult females. The web height was negatively correlated with females' body sizes, and adult females tended to make their webs at lower position than sub-adult females. Therefore, their preferable web-building site is expected to be the lower part of a hedge. However, this tendency was not clear within sub-adult females. During the reproductive period, an adult male searches for a web of a sub-adult or adult female and cohabits with the female for pre-copulation. Although cohabiting sub-adult females were obviously larger than solitary sub-adult females, the web height was not different between solitary and cohabiting sub-adult females. Considering the fecundity, which was clearly correlated with the body size, it is highly probable that the male tries to cohabit with the larger sub-adult female in order to increase his relative fitness irrespective of the sub-adult female's web height.

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