I was fortunate enough to find a new colony of Andrena bucephala last year, at my local churchyard in Warwickshire. This year I've been spending quite a bit of time watching and photographing there. Much activity involves sharing of communal nest entrances; I understand that this is a feature of A. bucephala nesting behaviour.
The colony is parasitised by Nomada hirtipes, with a reasonable amount of activity. I've also been surprised by the number of much larger flava-type Nomadas that are also invariably lurking at the nest holes. Today I saw two of these female Nomadas (at separate occasions) actually enter a communal A. bucephala nest hole. After several minutes they had not emerged.
I was wondering what could be deduced by this behaviour if, as I've assumed up to now, there there is a high degree of host/parasite specificity with Andrenas and Nomadas. Presumably, one of the following;
- I've made a mistake with one or more of the identifications (reasonably likely!);
- The flava-type Nomadas are just checking out the burrows but not actually parasitising them;
- The communal entrance is also being used by another Andrena species that the Nomadas are parasitising;
- The Andrena colony is being parasitised by two different Nomada species (most unlikely).
I'm new to bee watching and perhaps it's commonplace for Nomadas to randomly check out any Andrena holes looking for their specific hosts. I just hadn't seen this previously. I've attached an image of the Andrena and the flava-type Nomada and of N. hirtipes, at the colony.