BirdwatchInsects This article is more than 12 years oldSpecieswatch: Bird-cherry ermine moth
This article is more than 12 years oldThe bird-cherry ermine moth (Yponomeuta evonymella) is on the wing in Bradford. The moth, or rather its caterpillars, created a stir this May when they were reported to have stripped bare 15 fully grown trees in Shipley Hall Fields, a small but popular municipal park in the Frizinghall area.
It was not the thousands of inch-long caterpillars that caused consternation but their behaviour, as they wove giant webs over the whole trees, including the trunks, and even the railings of the park. People were so nervous that the park was deserted, and councillors demanded the moth larvae be zapped.
A council worker who went to look said 20 mature trees had completely disappeared under white silk: "It was warm, but it was as if a big frost had hit the park, about minus 40C with hoar frost. The vegetation had disappeared as in a film."
Bradford's pest control manager, Dennis Shipway, was not persuaded that the caterpillars needed to be sprayed and decided that nature should take its course, with the moths being allowed to complete their life cycle. He said pesticides would probably do more harm than good, to people as well as wildlife, and was optimistic the trees would recover on their own.
An inspection this month has proved him correct. There are still signs of the caterpillars, but only as remnants of their vast webs. Anne Heeley, the senior countryside officer, said the webs had hung down from the trees like white tights. The moths seem to have been pupating under the webs, because she saw adults hiding under branches waiting to fly away when night fell.
She had not seen the original infestation, but reported that the trees had leaves again. There were not as many leaves as usual at midsummer but the trees were certainly going to survive. She doubted that the trees could have been completely stripped, and perhaps some of the leaves had been hidden under the webs.
There are eight varieties of ermine moth that live in the UK, with the bird-cherry, with five rows of black dots on the forewing being the most common, particularly in the north. Some adults are so similar that the only way to identify them is by their caterpillars' food plant – in this case the native and common bird-cherry tree. It is particularly common in this park because the municipality had planted 40 of them as ornamental trees.
As the countryside officer pointed out, it would not be in the moths' own interests to kill off their host plant, because over the next few weeks the adults will be laying their eggs back on the same trees. The tiny caterpillars over-winter on the host plant and start munching again when the leaves emerge in the spring. This year's over-exuberance was probably caused by the favourable conditions of a sunny warm spring. Probably next year nobody will notice the caterpillars.
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