The Red Tailed Mason Bee

You may well have noticed some bees recently. One of the earliest solitary bees to emerge in spring is the Red Tailed Mason Bee, Osmia bicolour. They are very distinctive and make their nests in a very particular place.

The males emerge first, sometimes as early as March. They have yellowish bands. They are the followed in a couple of weeks by females which have distinctive red-banded abdomens, giving this bee its common name. The adults may continue flying well into July, so you have plenty of time to spot them. This species of bee is mainly found across southern England and the Midlands and South Wales. This is because it prefers chalk and limestone grassland and so is mainly in areas with this type of habitat.

Female Red Tailed Mason Bee making a snail shell nest. Copyright © John Walters, used with kind permission.

The Red Tailed Mason Bee is unusual in that the females make their nests in empty snail shells. A female bee works diligently to select a suitable shell then prepare the nest. She will then defend this vigorously. She will make several cells within the spiral of one shell, laying an egg in each cell. She will provide each egg with pollen as food for the larvae when they hatch. She will separate each cell with a glue-like substance called mastic. She makes this by chewing up pieces of leaf. When the nest is completed, she will plug the shell with more mastic and will then search for debris such as grass stems, fallen leaves and pine needles to carefully cover and camouflage it. She may also spread more mastic over the outside of the shell.

Entomologists think it is likely that this behaviour protects the shell and its contents from parasites and predators. Safe inside, the eggs will hatch and the larvae will develop inside the shell, feeding on their supply of pollen. They will then survive the winter as pupae, emerging as the next generation of adults the following spring.

So, if you spot an old snail shell, it’s worth keeping an eye on it; it may just become a nest for a Red Tailed Mason Bee. We’d love to hear about your bee sightings and to see your pictures. Get in touch with us using the comments below or by the Contact Us page.

Header image: Red-tailed mason bee, Osmia bicolor female. Image: František ŠARŽÍK CC BY 3.0

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