Potter Wasp Ancistrocerus nigricornis Nesting

I am fairly sure of the genus but the markings are variable, so it could be another species.

Yesterday morning was due to be a very hot day. My wife and I were standing in the back garden at about 8.45am when my wife pointed out a hoverfly on a flower. It was one of the smaller species but had a bright yellow scutellum, possibly a Sphaerophoria sp. So I fetched my camera.

When I returned, the hoverfly had gone. While I was looking around for it I noticed some activity at the top of a bamboo cane, which was supporting a tomato plant grown up against the wall of the house. I could just make out some yellow bands on a black abdomen. This was a wasp of interest.

At the top of the cane was a vertical hole, of about 4mm diameter, into which the wasps would enter, one at a time. They entered forwards and exited backwards. Everything happened very quickly. A wasp landing at the top of the cane was inside the hole in a second or less and departing ones flew off without hesitation, such that I had to prefocus (best guess!) each time. So, when I framed and exposed, the image I got when I pressed the shutter release button was of not what the wasp was doing but what it did next.

My access was limited by various heavy planters, full of plants, close to the back of the house. I then realised that the top of the cane might be photographable from the adjacent window, as it was but only with a very limited angle of view.

The session lasted about an hour. During this time I developed some understanding of the wasps’ activity pattern. One would arrive, enter the hole and exit a short while later. Two to three seconds later, another wasp would enter from about 90 degrees relative to the take-off direction. This would happen with several bees in succession, then there would be an interval of several minutes before the series of landings happened again.

The images show some carrying of a coarse, powdery material in the mandibles when the wasps were in the vicinity of the hole.

The flight was far too swift to allow framing and focus for in-flight shots. I had to prefocus and count two seconds before pressing the button. I finally got an acceptable image. The one prior to that shows the touchdown, with the wings still beating.

Towards the end of the session, the pattern broke up. One female arrived and spent minutes in the hole, at one time walking around on the rim and then reversing in, the only time I saw it. Then it poked its head out enough for me to get a shot. I thought the flash caused the immediate reversing into the hole but it did not exit again during the many minutes I continued to watch. I suspect that prolonged egg-laying was happening.

These images have been cropped to various degrees. The one with the head protruding has also had extensive white (painted sill) cropped out from the bottom left.

I have to say that I was very relieved when the session ended, as most of my view had been of very bright, white paintwork, such that I was at some risk of snow-blindness on the hottest day of the year!

Harold