Nomad Bees

I was delighted to see plenty of insects along the hedgerows of Laundry Lane in Sidford this week. It shows that some of the efforts to make space for nature are working. One group of insects I was pleased to see were small, black and yellow striped and looked like wasps, but they are nomad bees.

Nomad bees are so called because they have no home. Their other common name is cuckoo bees because they are kleptoparasites, they steal from other bees, particularly mining bees. Mining bees are solitary insects they do not live in colonial hives. After mating, a female will excavate a small burrow in the ground with several cells dug into the side walls. Each cell is filled with nectar and pollen and an egg laid and sealed in.

Nomad bees search out the unsealed mining bee burrows and, if the mining bee is out foraging, lay an egg inside. The mining bee does not realise this has happened and seals the completed burrow, trapping its young to their fate.

When the nomad bee hatches, it has powerful sickle-shaped mandibles and it will eat any eggs in the burrow, mining bee or other nomad bee eggs, and any bee larvae that might have hatched. Then it feeds on the pollen and nectar. When mature the bee pupates and over winters underground. It emerges and digs its way out of the burrow in the spring, just as the mining bees are emerging to dig new burrows and lay their eggs.

Nomad bees have evolved a complex use of scent to manage their success. The males fly backwards and forwards in areas where mining bees might nest to locate victim burrows. The males secrete a scent that mimics the scent of the host bees to mark the burrow entrances and this attracts female nomads.

During mating, the male transfers some of the scent to the female by pinning her down and stroking her antennae. It is thought this acts as a disguise so the poor mining bee does not realise her burrow has been invaded. It may also discourage other male nomads from trying to mate with the female.

Adult nomad bees feed on pollen and nectar but, as they do not collect this to feed young they do not have the pollen comb scopa on the legs, nor do they have much hair, and so they are poor pollinators.

There are over thirty UK species and they are very difficult to tell apart, even when the sit still. They vary in colour from the very wasp-like Nomada flava to the reddish-black Nomada obtusifrons. Many concentrate on a single host species, some will parasitise any of a closely related group of host species.

Looking on the bright side, I may not be able to identify them but I saw at least three different nomad bees in Laundry Lane, so there must also be at least three different species of mining bee victims too.