Tachina grossa – a big black fly!
The Yellow-faced fly or giant tachinid fly, Tachina grossa, is the largest European tachinid fly, between 1.5 and 2 cm in length. It is widespread in Europe, including the British Isles and is supposed to be a bumblebee mimic, but I am not sure which one it is copying. Probably an imperfect mimic of generally dark bumblebees. This species lays its eggs on the larvae of moths like the oak eggar (Lasiocampa quercus), on which they bore into and devour, eventually emerging as adults from the host pupa. (1) I think the yellow-buff coloured head and black body makes for a very attractive, if rather scary looking insect.
I came across it on elevated habitat, of heather and gorse, in hills behind Ortigueira, Galicia, Spain, in early September.
rcannon992 View All
I am a retired entomologist with a background in quarantine pests and invasive invertebrates. I studied zoology at Imperial College (University of London) and did a PhD on the population dynamics of a cereal aphid (Metopolophium dirhodum) in the UK. I spent 5 years with the British Antarctic Survey studing cold hardiness of Antarctic invertebates and 17 years with the Food and Environment Research Agency. My main interests now are natural history, photography, painting and bird watching.
I just saw what your picture depicts as a Lachina grossa. I thought it was a bumblebee but noticed it had very large wings. It was exploring a clump of freshly cut wet grass. My dog went towards it and it went after my dog. I am in my 70’s and always lived in BC, Canada and have never seen a fly like this before. Is British Columbia a natural habitat for this fly.? Thank you.
Dear Gail,
No, as far as I know, T. grossa is an Old World fly, only found in Europe and Asia. There may be something similar in N. America, or a bee? Best regards, Ray