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Saturday, 2 April 2016

Learning about bees, and their extraordinary and sometimes gruesome lives

I spent some time in Rainham Marshes' Cordite Store on Thursday taking pictures of a lovely little bee (only about 1cm long) that I found feeding on a dandelion flower.

Andrena chrysosceles

I'm a real beginner when it comes to identifying bees, but I had a look through my copy of Steven Falk's Field Guide to the Bees of Great Britain and Ireland and tried to at least work out the family or genus. I tentatively thought it might be a Lasioglossum.

The Facebook group UK Bees, Wasps and Ants is another wonderful resource for anyone interested in these insects, with several real experts on hand to help with identification, so I posted some pictures and asked if I was right about Lasioglossum. I wasn't! I quickly had a reply telling me that it was a male and was an Andrena species.

Andrena chrysosceles

This is where it starts to get interesting, extraordinary and, as I said, a bit gruesome. 

Someone pointed out that this bee was carrying a parasite - an internal parasite. Look at the tip of the abdomen in the last picture above. At the joint of the last segment you can see something sticking out between the plates. This is the head of the pupa of a Stylops parasite (I don't know what species).

Here's a closer picture. You can see the Stylops on the left, just below the tip of the wings.
 One of the Facebook group people said that this was probably a male Stylops about to emerge into his adult form.


I've now done some searching for information about Stylops. Their life cycle is remarkable. Both males and females develop as larvae inside the abdomen of various Andrena bees. A male like this one will eventually emerge as a flying adult, but the female is flightless and will spend all her life within the bee, with her head poking out between the plates of the abdomen. She releases pheromones to attract males and, once mated, she produces live larvae. These leave the current host to find another (unparasitised) host bee. They hitch a lift back to her nest, where they become internal parasites of her larvae while they develop into adult bees, and so the cycle continues.
Once a bee larva is parasitised, it develops into an infertile adult.

In the end, I did find out what species of bee this is. It's Andrena chrysosceles, which is one of the most common hosts for Stylops in Spring.