EXPERIMENTAL-STUDY OF FOUNDATION AND DEVELOPMENT OF ANELOSIMUS-EXIMIUS COLONIES IN THE TROPICAL FOREST OF FRENCH-GUIANA

Possibilities for new colony foundation in Anelosimus eximius (Theridi idae) were tested with isolated females (both with and without egg sac s) and with groups of individuals (groups from 150 to 250 spiders). Ex perimental groups were deposited in three different habitats: within t he forest, on the forest edge (where natural colonies develop most fre quently) and outside the forest (low savannah or areas cleared of vege tation, but in which plant life had started to grow back between the p ath and the forest edge). Isolated adult females had very low founding success: less than 13 % settled and spun a web; the presence of an eg g sac provided by investigators was not an influencing factor. Webs of isolated females had the same architectures as those of colonies with several hundreds of individuals. This web was a horizontal sheet link ed to a thick vertical network of threads. All groups of 150 to 250 sp iders established colonies in appropriate habitats. The colonies outsi de the forest, and more than 90 % of the colonies along the forest edg es successfully developed during the one month observation period. Con versely, 35 % of the colonies in the forest disappeared either a few d ays after being placed there, or one or two weeks after. In the latter case, spiders apparently left their webs, and all silk structures wer e left intact. No dead spiders were found in the webs. Average web sur face areas increased in all colony types with age, except for those pl aced in the forest. In these colonies, the number of individuals decre ased, and there were fewer egg sacs than in the colonies placed outsid e the forest. Results are discussed with regard to natural colony dist ribution along open paths and to the dispersive characteristics of thi s spider species.