Secret life of cuckoo bumblebees

Text  Meelis Uustal
Photos Piret Aasmäe
Translation: Liis
Cuckoo bumblebees
Of the about 250 bumblebee species in the world nearly 30 are cuckoo bumblebees. Taxonomists have placed them in the same genus as the true bumblebees. Genetically they are close, but regarding mode of life quite different.
The name cuckoo bumblebee comes from the similarity with the lifestyle of the cuckoo who lays its eggs in the nests of other birds. During evolution they have foregone a social mode of life. They have no worker bumblebees and they don’t take care of their offspring themselves but let their hosts do so. How does this work?
When the female cuckoo bumblebees wake up in spring, they enjoy nectar and start searching for the nests of their host species. Every cuckoo bumblebee has a basic host species and up to a couple of alternatives. Apparently they find the host species nests by smell – scientists have found that the cuckoo bumblebees smell very similar to their hosts. Having found the host nest the cuckoo bumblebee rushes in and attacks the bee queen. The bee queen begins to fight for her life and if the workers come to the rescue the intruder will be killed. If however the bee queen dies, the cuckoo bumblebee takes over command in the nest. At times the true bumblebee queen avoids a combat completely and gives up without a fight. She is then left alive but she has to become a servant of the cuckoo bumblebee and perform the same tasks as the worker bumblebees.
Having taken over the power, the cuckoo bumblebee starts laying eggs and the workers of the proper bumblebee begin to raise the offspring of the cuckoo bumblebee. From the eggs of the cuckoo bumblebee new queens and male bumblebees develop. Since no worker bumblebees hatch from the eggs of the cuckoo bumblebee it leaves the older proper bumblebee grubs alive in order to have a sufficient worker force in the nest. The reign of the cuckoo bumblebee ends when the proper bumblebee workers have died of old age and there is no longer anyone to care for the offspring of the cuckoo bumblebee.
By the way, the crafty mode of life, characteristic of cuckoo bumblebees, is by no means unknown to proper bumblebees. Several bumblebee species are known who likewise take over the nests of other species. This happens more often in climate zones with short and cool summers where each day counts, and a ready nest and the conquest of workers gives a bumblebee waking later in spring a strong advantage. There is then no need to bother about caring for worker bumblebees, and laying eggs to produce bumblebee queens and males can start at once.
Should we then label cuckoo bumblebees as pests and change our attitude to them? No, we don’t have to. Proper bumblebees and cuckoo bumblebees, hosts and parasites, have co-existed for millions of years and neither has annihilated the other. The only thing that endangers bumblebees as well as cuckoo bumblebees is first and foremost human activity – destruction of habitats and poisoning.
And do we regard cuckoos less kindly although we know the secrets of the cuckoo’s doings? Quite the opposite- it is difficult to imagine spring and the flowering of bird cherries without cuckoo calls. Let us be as kind towards the cuckoo bumblebees.
How to recognize a cuckoo bumblebee and what species occur in Estonia:
Bumblebee identification forms: LINK
Join the „Meie kimalased – Our bumblebees“ group on Facebook: LINK




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