Puzzling End of the Tree Wasp Colony - Wildlife.y2u.co.uk

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Puzzling End of the Tree Wasp Colony

Marion's Wildlife Notes
Dolichovespula sylvestrisThe long abandoned allotment had been cleared of its dense thicket of bramble and weeds, and access was now possible to its battered old shed. Swelled by past rainfall, the shed's rotting door was permanently wedged open, allowing easy passage to the queen tree wasp (Dolichovespula sylvestris) looking to establish her colony. We found her nest suspended from the underside of the shed roof. As their name suggests tree wasps usually hang their rather small ball-like nests (see second photo) in trees and bushes. However they'll also nest in cavities underground and in porches, cavity walls and sheds – hence our find.

Following hibernation over winter alone in a suitable crevice, the queen tree wasp will have emerged in the spring and sought a cavity free from temperature extremes and sheltered from the worst of the weather. Presumably finding the cover of our shed suitable, she will have constructed her nest using scrapings of sound wood mixed with saliva and chewed to form a grey paper like material. (Common wasps and hornets make the paper for their nests from rotten wood and so their nests are browner in colour and more brittle). The nest consists of horizontal tiers of hexagonal cells encased in a smooth outer envelope – all made from the grey paper. A small hole is left in the middle of the bottom of the ball to allow entry and exit.

Dolichovespula sylvestris nestOnce most of the nest is complete, the queen (which mated the previous autumn before hibernation) lays eggs in the cells. Once the eggs hatch and the grubs are revealed, the queen feeds them on nectar and a paste of chewed up insects that she has caught. The grubs then pupate and are sealed within their cells with a covering of wax. After a week or two, adult wasps emerge. At first these are all infertile female or worker wasps whose task is mainly to feed the next generation of grubs. Normally towards the end of summer more eggs are laid which develop into new queens and male wasps or drones. After this the “old” queen dies and the redundant female workers leave the nest in search of sweet foods – the cause of much nuisance to us at this time of year. Once they have pupated, the new queens and male drones also leave the nest in order to mate. Only successfully hibernating mated queens will survive the winter.

It was September when we found our nest. As it appeared quite old with no wasps about, we decided to take it down and have a closer look.(I hadn't read some websites then that refer to tree wasps as being more aggressive than some others!) Cutting it open with scissors we found 2 layers of paper forming the outer envelope. Inside were 2 to 3 layers of the hexagonal cells, some of which were empty and others still sealed with wax (see third photo). Several other cells contained the bodies of dead adult wasps.

Cells of a Dolichovespula sylvestris nestThe question was, why hadn't wasps developed in the still covered cells? - and why hadn't the wasps that had developed, emerged from their cells? It may be because the queen that built the nest had difficulty finding nectar and insects in the early spring, or it might be that she died without completing the colony. Or, it may've been that the colony was affected by parasites or other pests. It was certainly the case that as we took the nest down, several bluebottle-type flies emerged from it (suggesting by the way that the nest had probably been made this year rather than being quite old). Had they been drawn to the nest by the smell once the inhabitants had died, or had they played some part in its demise? More questions than answers!!!

If anyone can shed light on the above, we'd be glad to hear your thoughts.

Another wasp conundrum is why common wasps have recently been congregating around the bases of my friends potato plants just where they enter the soil. Are the wasps foraging for paper making material, or going after something sweet? Again we'd be glad to hear from you.

Marion
September 2015
Wasps on potato stems
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