Abstract
The nesting behaviour of the euglossine bee Euplusia surinamensis was observed on the Osa Peninsula of Costa Rica. We found that female bees nest in aggregations, re-use old nests, will take over abandoned nests shortly after the original owner is removed, and will fight off invading bees which attempt to take over their nests. We suggest that the nesting aggregations give bees the opportunity to use old nests and take over partially provisioned nests if the original owner disappears. In this way bees are able to increase their rate of egg laying above that which would be possible with solitary nesting and de novo nest construction.