The Great Pottery Throw Down

The title of this blogpost is taken from the latest BBC television series that has just finished screening in the UK. The premise for this series is based on the model developed for the hugely successful The Great British Bake Off, in which contestants compete against each other day-after-day to produce a variety of baked goods that are then judged by experts. Replace baked goods for ceramics and you will have grasped the intricacies of The Great Pottery Throw Down in its entirety. But what, if anything, is the significance of this to the study of invertebrates?

Well, having recently read Animal Architecture by Ingo Arndt and marvelled at the complexity and ingenuity of animals to create structures such as the heaped nests of wood ants, the towering cathedrals of termites and the delicately partitioned nests of paper wasps; I was rather taken with the notion of insects as ‘makers’. Serendipitously, I stumbled across the website of naturalist and artist, John Walters – specifically across his marvellous illustrations and accounts of Heath Potter Wasps, Eumenes coarctatus.

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Eumenes coarctatus. Source: Wikipedia

Potter wasps, Eumeninae, are the most diverse group of Vespidae, with over 3,500 species in 210 genera found throughout the world. Of these, 23 species in 9 genera are found in the UK. They derive their common name of potter (or mason) wasps from the fact that the females tend to construct nests from mud and clay. These nests can take multiple forms, but one of the most elegant (in my view) is the vase-shaped nest of Eumenes coarctatus, the solitary Heath Potter Wasp.

Using heather, gorse or dead grass stems as nesting sites, the female will build her clay vessel over the course of two to three hours. During this time she will repeatedly fly from a water source to a quarry site, where she will form a ball of mud in her jaws, which is then transported to the construction site where she builds the nest. Once she has shaped the neck and lip of the nest she lays a single egg in the chamber suspended on a strand of silk. She will then search for, sting and collect a number of small caterpillars, especially pug and horse chestnut moth larvae, from the heathland vegetation and then fills the pot with them. A final trip to the water source and quarry then provides enough clay to seal the pot with between 9 and 38 paralysed caterpillars trapped inside. A female heath potter wasp may produce up to 25 pots in her lifetime (2 to 3 months) and occasionally she will cluster pots as shown in the series of photographs below. It is possible that these clusters prefigure the development of eusocial colonies as seen in some other vespids.

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Development of a cluster of clay nest cells built by a single Eumenes coarctatus. Bovey Heath, Devon. Photos by John Walters.

When the wasp larva hatches from its suspended egg it drops onto the paralysed prey on which it feeds for about a week before pupating. The emergence of the adult depends on the timing of the building of the pot. If the pot was built before the end of June, the adult wasp will emerge 2 to 3 weeks later; if the pot is built in early July, the adult will still emerge in the same year; however, if the pot is built after this date emergence will be delayed until the following April or May.

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Illustration of Heath Potter Wasps taken from the field notes of artist and naturalist John Walters.

Though the E. coarctatus larvae are predatory, the adults feed on the nectar of heathland plants such as gorse, heather, bramble, angelica and alder buckthorn.

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Distribution map of Eumenes coarctatus in the UK. Source: NBN

Found on lowland heaths in England (from South Devon to East Sussex, and north to Buckinghamshire) the Heath Potter Wasp is classified as nationally scarce, though not designated a BAP species.

I also love Jean-Henri Fabre’s description of Eumenes taken from The Wonders of Instinct:

“A wasp-like garb of motley black and yellow; a slender and graceful figure; wings not spread out flat, when resting, but folded lengthwise in two; the abdomen a sort of chemist’s retort, which swells into a gourd and is fastened to the thorax by a long neck, first distending into a pear, then shrinking to a thread; a leisurely and silent flight; lonely habits.” 

More:

John Walters has also made a video of a wasp building a nest.

Michael Archer’s Key to British Potter and Mason Wasps is a very useful resource for identifying the various UK species.

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