Free masonry

There's a low wall on the south side of my house where I customarily sit and drink my morning coffee in the sunshine. Last year while doing this my attention was caught by the comings and goings of a wasp-like insect that landed on the wall for a few seconds and then flew off, over and over again. Looking closer I realised it was a mason-wasp engaged in the construction of a clay nest, plastered against the existing mortar so as to be perfectly camouflaged. She was bringing the raw material in the form of tiny stone particles which she cemented in place with clay formed from soil and her own saliva. A tiny area of dampness indicated the area she was working on.

The nest is both a cradle and a larder. The structure inside consists of a series of cells each one filled with a live caterpillar she has collected, paralysed but not killed with her venomous sting, and into which she inserts an egg. The emerging larva will feed upon the living food while it develops into a wasp. At the end of last winter part of the old nest had crumbled away revealing these cells.

So I was delighted to find that this year the wasp was extending last year's nest (which it on the left) all along the top of the stone like a tube. She will be adding additional cells, stocking them and laying her eggs. It appears that she knows the sex of her eggs: the female larva are bigger and require more food supplies so that their cells are larger than the those of the males.

The sunbaked shell of the nest, always on a south facing wall, is very hard and looks so much like the existing mortar that one would be hard put to spot it. It's an amazing insect artifact aimed at providing a perfect insurance policy for the offspring.

But one hazard lies in wait! And I saw it hovering nearby in the form of a tiny jewel-like insect of jade and ruby. It's called a cuckoo wasp and it aims to dart in and lay its own egg in the cell before it's sealed. Then, when the cuckoo wasp larva emerges it will kill and devour the mason wasp's larva and its provisions.

Last year's mason wasp is here.
Probably Odynerus spinipes but I could not be 100% sure of that.