2001 年 50 巻 2 号 p. 117-122
To reveal the factors that influence web-intrusion frequency by other web-building spiders, I investigated seasonal changes in the frequency of intrusion by spiders into webs abandoned by Metleucauge kompirensis (Tetragnathidae). I analyzed the effects of various conditions, including the size and density of host webs, and the life histories of intruding species. Intruders were mainly Tetragnatha praedonia of various size-classes, as well as small individuals of M. kompirensis. The average number of intruders per web was low between April and June because of the low density of intruding species and the high density of host webs. Thus, competition among intruders was probably not intense during this time. Early in the season, most insects remained in host webs were not consumed by intruders during the daytime, but may have been consumed with web silks by the web owners in the evening, before they constructed new webs. On the other hand, the average number of intruders per web was very large between July and early September. This may have been due to the low density of host webs and the emergence of newly born M. kompirensis spiderlings. The average number of insects remaining in webs during the daytime was low, as most insects were removed by intruders in the morning, when there was strong competition among intruders. Thus, the frequency of intrusion seems to depend primarily on the density of host webs and the density of intruding species.
