Wednesday, June 28, 2023

Explore Outdoors ~ Nomad Bees

Earlier this month I was watching the bees in my garden and saw this one collecting nectar from chive flowers. At first glance it looks like a wasp: thin waist, not very hairy, brightly colored, not collecting pollen. But it’s not a wasp; it’s a nomad bee (Nomada). Any other Wednesday I’d be sending you off on a 5-minute field trip, but I wanted to know how to tell the difference between nomad bees and wasps. 

So I asked entomologist and writer, Roberta Gibson. She wrote the very fun book, How to Build an Insect 

Me: So how do we tell the difference between nomad bees and wasps?

Roberta: There are a few clues, including their unique behavior. They are called nomad bees because they roam around close to the ground, searching for mining bee nests. Also, nomad bees have relatively small mandibles since they only use them to drink nectar and to hold onto flowers while sleeping. Many wasps have much larger mandibles that they use for catching caterpillars or spiders. Finally, if you have access to a powerful microscope, all bees have at least a few hairs with many side branches (also called plumose). Wasps have simple, straight hairs. 

Me: Nomad bees are pretty to look at, but I hear they are sneaky thieves in the bee world.

Roberta: Yes, they steal from mining bees (Andrena sp.). Mining bees dig tunnels in the soil, then visit flowers to gather pollen and nectar. When they return to the nest, the mining bee mixes pollen and nectar together to form a ball of food (bee bread) and lays her egg on top. Her larva will eat that food, grow, pupate and eventually emerge as an adult mining bee. 

Those sneaky nomad bees find the nests of mining bees and lay their own egg on the mining bee’s bee bread. The nomad larva hatches first and kills the mining bee egg. Then it eats the mining bee’s food. 

This behavior – stealing food that another organism has caught or stored – is called cleptoparasitism (also spelled kleptoparasitism). Because the nomad bee lays its egg in the nest of another bee, people sometimes call them cuckoo bees, similar to the cuckoo birds lay their eggs in the nests of other kinds of birds.

Me: Should I be concerned about seeing nomad bees – or other cuckoo bees – in my yard?

Roberta: Probably not. Some types of mining bees are good at hiding their nests, closing up their nests, and keeping vigilant against nomad bees. Cleptoparasites only do well if their hosts (mining bees) are doing well. There are far fewer nomad bees than mining bees. If you want to help bees, the best thing to do is to plant a diverse selection of wildflowers so all bees have a good supply of pollen and nectar throughout the growing season. 

Thank you, Roberta! And I agree, planting more flowers is something we can all do. Check out Roberta's blog, Growing With Science. She has observed different kinds of cuckoo bees visiting her flowers, and posted about them here and here.

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