Bombus vestalis/bohemicus i/d in the field
Observation - Bombus vestalis/bohemicus i/d in the field - UK and Ireland. Description: The commonest bumblebee about at the moment (mid-August). This is a large cuckoo bee, instantly recognisable from all but B.bohemicus by the yellow side-flashes on the border of black/white on the abdomen. Even at a distance, the honey-coloured 'boa',
The commonest bumblebee about at the moment (mid-August).
This is a large cuckoo bee, instantly recognisable from all but B.bohemicus by the yellow side-flashes on the border of black/white on the abdomen. Even at a distance, the honey-coloured 'boa', the lack of a strong yellow band on the front of the abdomen, the loose thin furring of the elongated abdomen, and the thin 'shoulders' make it instantly distinguishable from the B.terrestris (mostly male) still about. The dark shading around the wing veins and the rough, thin hind tibia are visible on a close-up like this, but by the time you get close enough to see them you know what the species is anyway. Many books try and get you to do this i/d in reverse, starting with the hind tibia, but this isn't remotely necessary.
B.sylvestris female is possible, but is smaller and has a very different shape with curled-under abdomen and usually a dark tip (red in male).
You could try counting the antennal segments on this photo to sex the bee before you start - it is sharp enough and detailed enough to be easy...but it isn't! Even with the excellent illustration of a numbered antenna in the New Nat key (the only one I've found that actually gives this crucial info) showing what counts as segments 1 & 2, look at the next ones along. Is that a long segment 3, or segments 3 & 4? Or even short segments 3,4 & 5? Then look at the tip - is there another tip segment hiding below what appears to be the end? OK, now try doing all that, as recommended by many books, to a struggling bee in a specimen tube! No, counting antennal segments like many features, is fine for Dead Bees, but not much use in the field compared with other more obvious features.
So far the only way to i/d vestalis/bohemicus for sure is to pull the bee apart to look at the genitalia. All the ones done here so far have turned out to be vestalis, but the large size of this female, coupled with the honey colour on the band (cf yellow) could well turn out to be good enough field characters. The amount of yellow on the side-flashes is a difficult one to judge in the field.
The males have more yellow on the thorax - usually bands front and back, with the front extending on to the top of the head (the latter I think could be a more reliable field character than the former). Pretty much all my vestalis are females at the moment, which is odd, as the consensus is that males are much more frequent than females now (Benton, New Nat 1998). Perhaps this will be the case a bit later.