Costs and Benefits of Brood Care in the Hawaiian Happy Face Spider Theridion grallator (Araneae, Theridiidae)

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Abstract
The costs and benefits of maternal care in the Hawaiian happy face spider Theridion grallator were studied in the field and laboratory. Adult females were usually found as solitary occupants of the underside of leaves in Hawaiian [USA] forests. Individuals generally laid one egg sac, but could lay another if the first was lost. They guarded their egg sacs aggressively, which appeared to be essential for preventing predation, since no egg sac survived in the absence of the mother. Maternal care continued after hatching, with the young feeding communally on prey caught by the mother, being unable to capture prey on their own. This period of posthatching brood care was vital for the reproductive success of the female. Several spiderlings were adopted into the broods of apparently unrelated females. The implications of this phenomenon are discussed.