This is one of those posts triggered by a single, initially bemusing, observation. In this case, a cluster of smallish-to-medium (approx 10mm long) bees in the empty seed head of a Snake's-head Fritillary (Fritillaria meleagris) flower.
Here you can see four bees clustered into the old seed head - at most I found eight (five in one head and three in another, with only the most upright stems chosen). I had to wonder what they were doing - roosting, some type of reproductive behaviour, or something else entirely? Also, I wanted to know why there appeared to be two forms - one with creamy-white hairs, another with orangey hairs. So, first stop - identification.
This bee has clear abdominal hair bands and has posed helpfully so that its wing cells can be seen. I don't want to delve too deeply into diagnostic morphology on this occasion, but there are some features that need to be looked at. Firstly, there are three submarginal cells (below the costa or 'lump' on the front edge of the forewing, and the 3rd one (nearest the tip) is longer than the middle one. Another feature might be the grooves below the antennae but these are obscured by the hairs on the front of the face. However, what about the eyes? Are they hairy or not? The photo above suggests they are, but...
Here, you can see that the eyes are not hairy - it's important to look from the right angle! Now, we need to look at the antennae and tarsal ('foot') segments.
Looking closely, it is clear that the antennae seem knobbly (in other species they are smooth and cylindrical).
OK, not the clearest picture ever, but the last tarsal segment (the one that has the claws) is broadened, a bit like the shape of a teardrop, rather than being narrow and elongate - here it also had a reddish-brown colour.
So, what does this tell us? Well, working through the various options, it brings us to the genus Melitta and not the other genera that look very similar such as Andrena. There aren't many species of Melitta in southern England:
- M. haemorrhoidalis has only faint abdominal bands in the male and red hairs at the abdominal tip in the female. It isn't this (as it happens I know this species so could discount it easily).
- M. tricincta only feeds on Red Bartsia (Odontites verna) - there isn't any here.
So, to confirm, I watched for a while and saw the males eventually move from the seed head and start scouting around the clover, though they didn't land or feed. Then, an individual - a female I think - did appear and fed for some time.
This specimen of M. leporina on white clover shows not only the white hair associated with old age (I know the feeling...), but also the wear on the wings - you can see the tattered edges.
So, what's going on? Well, I did a bit of reading and it turns out that M. leporina males form little temporary roosts near clovers and vetches which they use as a base to seek females. The males rarely stop and feed, but the females do - then in the evening when the temperature cools, they return to the roost. I imagine the clustering keeps them warm, and using only taller stems provides some protection from nocturnal ground-dwelling predators. In the end, it turns out that this behaviour involves both roosting and reproduction - it's also good to see in our bee-friendly garden as this species, in Britain, is found mainly in SE England and is declining - it isn't currently listed as 'scarce' or 'rare', but as Edwards (1998) says, this status should be reviewed. I'll keep looking out for them, and their unsurprisingly scarce parasitic bee Nomada flavopicta, and hopefully the seed heads won't stay empty...
Baldock, D.W. (2008). Bees of Surrey. Surrey Wildlife Trust, Woking.
Edwards, R. (ed.) (1998). Provisional Atlas of the Aculeate Hymenoptera of Britain and Ireland. Part 2. BWARS/BRC, Huntingdon.
Falk, S. (1991). A Review of the Scarce and Threatened Bees, Wasps and Ants of Great Britain. NCC, Peterborough.