Food exchange by the mother to her brood is a frequent phenomenon in social arthropods. In the subsocial spiders of the genus Anelosimus Simon, 1891, maternal regurgitation to offspring plays an important role in the survival of the colony. Regurgitations also occur between subadult males and females in Anelosimus vierae Agnarsson, 2012. In order to examine the effects of supplementary food on the subadult male's development towards maturity, we carried out two types of trial: groups of subadult males and female siblings and non-siblings were weighed, and cephalothorax and leg I in adult males were measured. Our results suggest that the supplementary food obtained by males from sisters allows the acquisition of larger size. Besides weight gain, males fed by females reached larger sizes of leg I femur and tibia. Leg I could be important in intrasexual competition, given that males with larger legs are more likely to win agonistic encounters. This also has positive implications for access to females.