Aggregation Behavior in Spiderlings: a Strategy for Increasing Life Expectancy in Latrodectus geometricus (Araneae: Theridiidae)

Abstract

Studies on the biology of Latrodectus geometricus are scarce, especially on the behavior and life expectancy of the species. In this study we investigated the importance of the aggregation behavior of juveniles on life expectancy and longevity of the species. Egg sacs were collected in the urban area of Dourados- MS and transferred to the laboratory. The spiderlings hatched were separated into two groups: spiderlings aggregated and isolated, kept in the presence of luminosity. The same tests were run with egg sacs deprived of luminosity. A calculation of entropy was performed for all cases. Individuals grouped held under light exposure showed 14.3 days of life expectancy and 46 maximum longevity and 14.8 days of life expectancy and 32 days of longevity when isolated. For individuals grouped and deprived of light life expectancy was 29.8 days and maximum longevity 85 days and 19.3 days of life expectancy and 26 days of maximum longevity when isolated. The entropy of individuals kept in the presence of light, when grouped was H=0.692 and when isolated H=0.377. For individuals deprived of light, the entropy was H = 0.628 when kept grouped and H = 0.143 when isolated. Therefore it is concluded that the aggregation behavior and luminosity influence the longevity and life expectancy of spiderlings. Cannibalism must be a strategy to acquire food reserves contributing to the survival of a small number of individuals.