Analysis on the dispersal pattern of newly introduced Latrodectus hasseltii (Araneae: Theridiadae) in Japan by spider diagram.

The dispersal pattern of the widow spider Latrodectus hasseltii (Araneae: Theridiadae), in Osaka Prefecture, Japan, was analyzed from accumulated survey data of spider distribution. All confirmed infested points from 1996 to 2002 were plotted on a map, and infested points in each survey year were connected with the nearest previously confirmed points. Expansion patterns of the confirmed habitats were analyzed by year and dispersion distances were classified by using spider diagram, one of method of geographical information system spatial analysis. L. hasseltii moves by walking step by step on the ground, mainly in coastal areas during early stages of infestation, and also can be conveyed over distances by various vehicles, mainly in inland areas. These analyses show L. hasseltii does not move by ballooning.