A study of social interactions and web dynamics in the spider Anelosimus sp., (Theriidae) in Monteverde, Costa Rica

Sociality in spiders represents serious evolutionary drawbacks, yet persists in some 20 species. Sociality of an undescribed species of spider, Anelosimus sp. (Theriidae), was studied in Monteverde, Costa Rica. The social interactions that were considered were: prey capture, kin recognition and web dynamics. I observed prey capture, whether adults or juveniles were attacking, and how long it took to first contact the prey. Adults preferentially attacked larger prey, while juveniles preferentially attacked smaller prey (p = 0.001, 2 = 10.517, df = 1, n = 23). There was also a trend showing that spiders in multiple-spider webs contacted prey faster than those in single-spider webs (p = 0.09). These results suggest that an increase in efficiency and a sharing of the prey-capture burden act as mechanisms to help make social living beneficial. A second part of the study consisted of introducing foreign spiders, both juveniles and adults, to webs and recording the reaction. The introduced adults were almost always shown aggression, while introduced juveniles were never shown aggression. This suggests the presence of kin recognition, as foreigners were recognized; smaller juveniles were largely ignored, while large foreigners were attacked and chased off. Size could be the mechanism for determining when juveniles finally disperse from the natal web. Finally, I found a positive relation between web volume and number of spiders (p = 0.001) and number of smaller webs within 50 cm (p = 0.08). This indicates that the web must increase proportionally with each additional spider in a brood. My study suggests possible mechanisms for making social living beneficial despite the serious evolutionary drawbacks. La sociabilidad en las arañas representa serias desventajas evolucionarías, encontrándose en alrededor de 20 especies. El comportamiento social no descrito en las especies de Anelosimus sp. (Theriidae), fue estudiado en Monteverde, Costa Rica. Las interacciones sociales que fueron consideradas son: la captura de presas, el reconocimiento de parentela y la dinámica de la tela.https://digitalcommons.usf.edu/tropical_ecology/1506/thumbnail.jp