Cuckoo bees make up about 20% of all bees and are rather naughty bees. The cuckoo bee will lays lots of eggs in the nests of unrelated pollen collecting species. The cuckoos larvae then hatch out before the hosts larvae and eat all the pollen in the store and then will kill and ear the host bee larvae. The cuckoo bees do not themselves have a pollen scoop like other types of bees - but many hatch with a large jaws with which they can attached other larvae.
The cuckoo bees can either enter the nest by stealth or by force. Some species creep into the nest and become part of the colony laying eggs wherever possible. Others aggressively attack the nest, killing any worker bee in their way and ultimately killing the queen on the colony.
There are around 4000 species of Cuckoo bees.