Stylopised

I spent much of the day in the garden, doing a rough tidy of the long border at the front of the house. There was a definite feel of spring in the air, and noticeably more invertebrates out and about. Interestingly there were several hairy-footed flower bees patrolling the border where I was working, but they seemed completely unfazed by my activities, simply zooming around me most of the time, but occasionally screeching to a halt in mid-air (I may have exaggerated slightly there, for effect) and staring at me for a second or two before zooming off again.

Over the course of the day I added a Brimstone butterfly, two beetles, a green shieldbug, a couple of hoverflies, and several solitary bees to my year list. This is a chocolate mining bee, Andrena scotica, one of two individuals that I found close together and within a few seconds of each other - but definitely different specimens, because this one is stylopised and the other was healthy.

If you're able to view this image full-screen, you should be able to make out a pale area below one of the hair fringes towards the bottom of the bee's abdomen. This is actually the head of a female Strepsiptera, or twisted-wing fly, a parasitic insect that's so poorly understood, it's not yet been decided whether it's a fly at all, some authorities believing that it might be more closely related to a beetle. These parasites attack Hymenoptera (that is, bees, wasps and ants), and some Homopteran bugs such as leafhoppers, but the Andrena mining bees are especially affected. Falk states that almost all early emerging hawthorn mining bees (Andrena chrysosceles) are stylopised individuals, and that was certainly the case with the one I found in the secret garden today, which was the first A. chrysosceles I'd seen this year.

If you'd like to read about Streptisera in some detail, there's a good page on the Royal Entomological Society web site; but in brief, the female parasite in this photo, which is commonly called a stylops, will live her entire life inside the bee, altering the host's behaviour and most probably preventing her from mating and nesting. The female stylops is blind, legless and unwinged and feeds on the haemolymph of the bee, and her only function is reproduction. She protrudes her head like this to emit a pheromone and attract a winged male, which will have developed and pupated inside a different bee before emerging. The good news is that he cannot feed, and only has hours in which to fly around in search of a female before he dies. If he succeeds in his quest, mating takes place on the body of the bee, and the fertilised eggs then develop inside the body of the female stylops. The larvae emerge and disperse in search of a new bee host, and if they find one they burrow through its cuticle  and the cycle begins again.

If you're not already completely grossed out, there's a film here of a male stylops emerging from a male Andrena scotica.