bumblebees try to break into the nest, sentry bees attack them with their stingers. These attacks are often arranged so that several bees throw themselves onto the intruder at the same time. Bees can also defend their nest with body-to-body combat: this happens when ants want to enter the beehive. The bees push them back with their legs and beat their wings to create a current of air that will blow them away.
Bees devoted to the harvest become collector-bees. They collect nectar, pollen and propolis, a resin which is made from plant buds and water. Pollen and propolis are carried to the beehive storage cells on the bees' back legs, whereas nectar and water are carried in the honey sack.