Most spiders are aggressive, socially intolerant predators; however, broods develop inside a common site and thus should benefit from restraining aggression at this time and until they disperse. I tested single and mixed-brood groups of Misumena vatia (Clerck 1757) (Thomisidae) spiderlings that had just emerged from their nests to determine whether they cannibalized other young under crowded conditions comparable to the immediate area of their nests, and if so, whether they distinguished between sibs and non-sibs. Young M. vatia provide an interesting test case, since some broods remain in close contact for a short period of time after emerging from their nests. Mortality remained low over one month in provisioned young under crowded conditions, and no cannibalism occurred in these individuals. Cannibalism remained low in most broods of unprovisioned young, even though most of them eventually starved over this time. Just-emerged spiderlings placed in the field for three days and then run similarly also showed initially low tendencies toward cannibalism. However, larger free-ranging spiderlings that overlapped in size with provisioned spiderlings in the study cannibalized freely when confined similarly to the other spiderlings in this study. During this period the spiderlings showed no clear evidence of distinguishing between sibs and non-sibs.