An nesting aggregation of Mellinus arvensis Wasps

30th August 2013
I spend quite a bit of time in the local village churchyard photographing insects and other invertebrates; mainly solitary bees. I had a photographic display in the church too recently and I'm getting reasonably well-known locally as a keen insect photographer.

A local resident who had spoken to me a while back and taken one of my business cards, telephoned me this week and asked me if I'd like to come a look at some unusual wasps she had in her garden. She said that they were digging holes in her block-paved patio and had been doing this, at the same time of the year, for several years.

I was intrigued to go and have a look and hopefully, to get some photographs. I was surprised when I got there, as there were about forty active nests. Each one had a sizable "volcano" of coarse sand that had been excavated, some undisturbed and others disturbed by the residents walking over the area to their back door. There was no apparent activity from the nest-builders when I first got there, so I decided to wait and see what happened. It didn't take long before I saw some activity in one of the nest burrows, with the occupant preparing to emerge.

I could see that it was a species of wasp, but didn't recognise it. She was deep in the burrow and just visible, but she then came to the entrance. I was able to get some initial shots. Another wasp then emerged from an adjacent burrow.

The longer I waited, the more activity I saw. Some of the nests were still under construction and the female would emerge backwards, pushing a small amount of sand. I told the owner of the house that I didn't recognise the species (I'm not that knowledgeable on solitary wasps), but that it was a species of "digger" wasp. She said that she and her husband had seen the wasps returning with flies.

No sooner had she said it, than this wasp returned with such a fly. I saw several returning from successful hunts and dragging their prey down into the burrows.

As soon as I got home I processed the images and consulted my trusty wasp book; Wasps of Surrey by David W. Baldock. This is an excellent reference work, Surrey hosting more species of bees, wasps and ants than any other county in Britain. I soon found out that this was a colony of the Field Digger-wasp - Mellinus arvensis. They fly quite late in the year and often nest in aggregations. They are common and widely-distributed in the UK. Typically, they excavate a vertical nest hole often more than 30 cm deep. This contains one or more brood chambers, each provisioned with up to a dozen large flies. The flies provide food for the developing larvae.

I was really pleased to have been told about this nesting aggregation. This is a "new" species for me and provided some interesting photographs. It would be nice to see some males emerging next year and to get photographs of those too.

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