Abstract
Since the redback spider, Latrodectus hasseltii Thorell, was first confirmed in November 1995 in the Osaka Bay area in Japan and became established in high density in areas adjacent to the Kansai International Airport, its distribution range continues to expand. Based on the outcome of the redback spider surveys, we implemented address matching and tabulated the survey year, the address of confirmed infested sites and number of webs by year using GIS computer software and digital maps. We furthermore mapped the expanded areas of the spider infestation by year and address and produced density distribution maps for each year from 1995 to 2001 and a map for the period of the surveillance. In addition, since biting cases have been reported, we examined the relationship between the spider density and the number of biting cases. From our GIS analysis it became clear that the distribution range of the redback spider clearly continues to expand in Osaka Prefecture and the expansion of the spider occurred gradually in some coastal areas and dispersed from the densely distributed areas to the more inner areas in Osaka Prefecture. These analyses also show that the number of biting cases by the redback spider will increase in Osaka and surrounding prefectures infested with redback spiders.
