Mellinus arvensis dangling prey

1. The following observation was posted on the BWARS Forum by Keith Balmer:

Today I twice observed Mellinus arvensis females dangling their diptera prey over the edge of oak leaves for several minutes at a time, apparently suspended by their tongues(?), then flying with the fly slung beneath them supported by their legs to another leaf only to repeat the dangling process. Eventually they flew off with the flies, presumably to their burrows.

Can anyone tell me what this dangling business is about please? The flies seemed immobilised throughout, so I couldn't quite convince myself that they were waiting for their prey to become subdued, but that's my only theory right now.

Response from Duncan Jackson:
A reasonable guess is that they are inspecting their prey for indications of parasitism. They don't want to provide their offspring with parasitised prey, so this is a major decision.

It's just my suggestion, but someone may know better.

2. A further observation from Richard Becker in Montgomeryshire of an adult Mellinus arvensis feeding on a fly:


Recently I was attempting to photograph Aculeates around an area of flowering Heather (Calluna vulgaris). It was sunny and warm and several female Mellinus arvensis wasps were around the heather, apparently hunting the many flies feeding on the flowers. These are a species that provision the nest cells with various flies. I noticed one Mellinus, carrying something, come into land on a bare earth bank next to where I was standing. When I focused through the camera viewfinder I was surprised to see that she was in the process of eating a fly (probably a Greenbottle, Calliphoridae). The head of the fly had already gone, and over the period of a couple of minutes she ate the muscles of the thorax and part of the abdomen. Eventually she flew off leaving behind the cuticle and some chewed remains.




Photos: Keith Balmer