Persuasive Burglar

We have spent a week walking in the beautiful Elan Valley in Mid Wales. Despite seeing herons, kingfishers, kites, buzzards and a goshawk we were never close enough to get a good photograph. On our last day we were exploring in the pine woods above Garreg-ddu dam when we discovered these beautiful insects. Rhyssa Persuasoria (which translates as Persuasive Burglar) is a parasitic species and the largest ichneumon fly (or wasp) in Britain, and one of the largest in Europe.

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Also known as the Sabre Wasp or Giant Ichneumon it is common throughout Europe, Australasia, the Near East and North Africa. We had never seen one before and were amazed by it’s size and beauty. The females can grow to over 40mm plus another 40mm for the ovipositor and despite their fearsome appearance they are completely harmless to humans. But to the larvae of the Wood Wasp, Horntail, Longhorn Beetle or Great Capricorn Beetle this creature is your worst nightmare. Wikipedia describes the predatory behaviour of the female as follows:

The female searches for hosts, which live within fallen timber or other trees. She may detect them through the smell of their faeces, which are sometimes contaminated by fungi, or by sensing their vibrations within the wood. When she finds the right spot she drills deep into wood (which can be inches thick) by its hair thin ovipositor by rotating the two halves backwards and forwards very rapidly. She lays her egg which is deformed into a slender, threadlike shape, on larvae living in the timber, which become a food supply and an incubator for the egg, until it is fully grown. It keeps it’s victim alive as long as possible. Dead larvae rot quickly, and this ruins the meal and the rhyssa persuasoria cannot grow. First the parasitoid eats the fat bodies of the larva, then the digestive organs, keeping the heart and central nervous system intact for as long as possible. Finally, these are consumed as well and the long-suffering victim dies, leaving an empty caterpillar shell in which the victorious insect may choose to pupate.

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We watched them hunting for several hours and managed, with the help of a small reflector, to get this picture of the female drilling down into the wood. If you see them in your garden or in the house, please treat them kindly.

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Author: Hares on the Hill

I am a designer and photographer. I live with my wife and our two dogs in the Welsh Marches, a land full of history, legends, mountains, rivers and dragon's breath; a place where animism thrives. To our north are the Cambrian Mountains, the Elenydd, a vast plateau so ancient that its mountains now have the appearance of steeply rounded moorland hills; to the east is England; to the south stand the Black Mountains and in the west the Brecon Beacons rise around the twin summits of Pen y Fan and Corn Du, the highest mountain in West Wales.

2 thoughts on “Persuasive Burglar”

    1. Hi James

      I’m glad that you enjoyed the post, they are amazing creatures. If you are in a conifer wood between June and August look out for them on fallen logs in sunny clearings. If the weather stays warm you may still be lucky this September as everything seems to be late this year.

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