Cannibalism and prey sharing among juveniles of the spider Oedothorax gibbosus (Blackwall, 1841) (Erigoninae, Linyphiidae, Araneae)

In a terrarium experiment, juvenile cannibalism in the dwarf spider Oedothorax gibbosus (Blackwall, 1841) was very high - up to 99\%. More first juveniles were cannibalised at higher initial densities, and there was no effect on this cannibalism from offering different prey species. Although in their natural environment spiderlings may more readily evade one another, this terrarium experiment demonstrates the drastic effect of juvenile cannibalism. Larger first juveniles are apparently more prevalent among the cannibals, and juvenile cannibalism among similar sized spiderlings is less frequent. Prey sharing observed between similar sized first juveniles is not a social behaviour, but is rather a forced prey sharing resulting from competition among equally strong juveniles that are unable to defend their prey items from one another. Larger first juveniles do not tolerate smaller ones sharing their prey.