Dark Chocolate

Compared with last year, this invertebrate season has got off to a rather slow start. This is especially true of hoverflies, of which I've only recorded four species so far, compared with the eight I'd seen by the same point last year. Bees are also running slightly behind schedule, though butterfly numbers are up - which I can only hope bodes well for the season, because last summer was a truly terrible one locally for butterflies.

Today was cloudy and not especially warm, so I didn't have high hopes on the invert front, but in the event it turned out to be a good day. I've posted ten of my best finds to my Facebook page, if you'd like to see them. This is the first Chocolate Mining Bee (Andrena scotica) I've seen this year, and I think she's beautiful - but in common with the first Chocolate miners of last year (20th February) and 2023 (18th March) she's stylopised, which makes it almost certain that she won't be able to fulfil her own biological imperative, but instead will spend her entire life hosting the very strange endoparasite Strepsiptera, while it strives to complete its own life cycle. 

If you want to locate the stylops here, count along the bee's abdominal segments from right to left, and you should be able to see a brown lump protruding below the thick hair fringe on the distal margin of the fourth segment. This is the head of a female Strepsiptera, which will now emit pheromones with the aim of attracting a male. If a male parasite finds a female within the few hours he can live independently of his own host, he inseminates her through a canal behind her head. Her eggs hatch inside her, and the larvae then emerge via the same canal while the host bee gathers pollen from flowers. The larvae attach to other bees in order to be carried back to their nests, where they will enter the bodies of the bee larvae and develop along with their hosts. 

There's a quite disturbing film here of a male Strepsiptera emerging from a male bee - also an Andrena scotica in this case. But many other bee species (though the miners are especially vulnerable), and some bugs such as leafhoppers, are parasitised by Strepsipterae, and I've read nothing to suggest that a breeding pair needs to have developed within the same host species. Hosting a stylops seems to alter a bee's behaviour in a number of ways, one of which may be to make them emerge early from their nest, because it's often stated that a high proportion of the mining bees seen early in the season are stylopised.