Crabroninae Aylesford Kent

Crabroninae wasp leaving nest

My wife and I were in the UK in June visiting our daughter who lives there and our son who was working there for a week. Having spent much of the summer watching Dasyproctus wasps in Jervis Bay I was interested to see what wasps frequented fallen logs in the UK. My first discovery was in London in Kensington Gardens where I found two different species of Ecteminius wasps searching for nesting sites. These are solitary wasps, who nest in rotting wood and use their substantial mandibles ending in teeth to excavate their nests. Like the Dasyproctus they hunt flies and seem to be fairly common in the UK. For more information look at the article on The Lancashire Wildlife Trust.

We then spent some time in Aylesford, Kent where I came across this log at the end of Rugby Pitches in Ferryfield. It was full of insects. Bumblebees were nesting under the log, a Leafcutter Bee was nesting in the end, carpenter ants had a nest halfway up and at the top were Crabroninae wasps. There is a cut area just above halfway which was frequented by common wasps collecting wood to make their paper nests. Above that is another cut bit facing up and the home to 10 Crabroninae nests.

iNaturalist identified them as Crabroninae and I was unable to get a better id from my reading, so I am sticking with their id. These are small wasps around 7mm long and tend to live in what I assume are family groups. The most active nest had at least 8 wasps as on one occasion I counted 8 going out of the nest before 1 entered. Most of the other nests appeared to have only 2-4 occupants based on the amount seen entering and exiting and frequency of flights.

They were all hunting the same prey which appeared to be green flies of aphids. This one is returning to the nest with the paralyzed fly. It will be taken to a cell where it will be added to other flies. Once the cell is full an egg will be laid which will feast on the paralyzed flies once it hatches. Around a third of the returning females had flies to add to the cells.

Interestingly the wasps did not have it all their own way and were parasitized by flies of the Eustalomyia genus. The fly below waited patiently near the nest until it felt the nest opening was unattended, it then did a quick check and laid an egg a centimetre into the nest.

This picture is the quick check. On this occasion it was laying an egg in the most active nest. The day before it or another one had laid an egg in a nest a few centimetres away. The wasps appeared to be aware of its presence but did nothing to discourage it.

The other danger came from the carpenter ants nesting in the log. They continually patrolled the area and would often pass over wasp entrances but normally did not interact with the wasps. On one occasion something changed and a small group of ants infiltrated one of the nests and carried the wasps' prey back to their nest. The wasps appeared perplexed and would enter the nest a small distance and then quickly retreat. They would wait at the entrance intently observing but did not attempt to protect their nest. They would fly away, returning a minute or two later and do the same again.

Unfortunately I was only in the UK a short time so my observations were incomplete. The following PDF will provide more information on my observations.

CRABRONINAE UK.pdf

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