INFLUENCE OF COLLECTIVE FEEDING ON WEIGHT GAIN AND SIZE VARIABILITY OF ANELOSIMUS JABAQUARA LEVI 1956 (ARANEAE: THERIDIIDAE) by MARCELO DE OLIVEIRA GONZAGA 1,2) and JOÃO VASCONCELLOS-NETO 3,4) ( 1 Pós-graduação em Ecologia — IB, Universidade Estadual de Campinas; 3 Departamento de Zoologia, Instituto de Biologia, Universidade Estadual de Campinas, Campinas — SP, Brazil) (Acc. 9-X-2002) Summary Differences in the size and weight of spiders within colonies may be an important factor for determining dispersion and food distribution among nestmates. In this study we report on the variation in size of spiders from 27 colonies of A. jabaquara, collected during one year. We also conducted an experiment under laboratory conditions to test if prey size, and consequently, collective or individual capture behaviours, inuence the establishment of weight differences. Female size variation within colonies was high, increasing slightly from March to September. However, from November to January the variation was much lower, probably as a consequence of the emigration of large spiders during the reproductive period. Spiders that fed on large ies in the laboratory experiment grew more and collective feeding seemed to induce a larger variation in weight among individuals. These results indicate that collective feeding promotes an unequal distribution of food in A. jabaquara colonies. Keywords: Anelosimus jabaquara, social spiders, collective feeding, size variability, prey capture behaviour. 2) Corresponding author’s address: Departamento de Zoologia, Instituto de Biologia, Universidade Estadual de Campinas, Campinas — SP, Brazil. CP 6109, CEP 13083 970; e-mail address: mogonz@unicamp.br 4) We thank Rogério Parentoni Martins, Paulo Sérgio Oliveira, Hilton Ferreira Japyassú, Cristina Rheims and Adalberto J. Santos for helpful comments on the initial version of the manuscript. We are also grateful to Brian Wisenden and two anonymous referees for their valuable suggestions. This research was supported by Fapesp (proc. 97/05353-4). © Koninklijke Brill NV, Leiden, 2002 Behaviour 139, 1431-1442 Also available online -