Spring 2019 has been notable for the number of reports of web forming caterpillar nests. In early April a farmer near Chatteris rang to tell me that a mixed native hedge which I had planted 3 years earlier had a whole lot of football sized webs and caterpillars were eating the emerging leaves. I told him not to worry, that the caterpillars would soon pupate and the hawthorn would recover.

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At the end of May he rang again to say that over 300 metres of hedge was now totally defoliated. On visiting the site we found that for a mile all roadside bushes were completely stripped of leaves, not just hawthorn but dog rose, dogwood, even elder. The recently planted hedges in the farmer’s fields were stripped from end to end, only guelder rose and wild privet seemed to be resistant.

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The culprit was caterpillars of the brown tail moth Euproctis chrysorrhea. Their webs contain irritating hairs which protect the caterpillars from predation by birds. Once again I told the farmer that there was nothing to be done and that the hedge would recover, but with rather less conviction than I had said it in April.

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The farmer then went on to tell me of another hedge on his farm where webs had appeared at random intervals. These were the work of caterpillars of the spindle ermine moth, Yponomeuta cagnagella. Small patches of spindle had been planted in the hedge and every plant had been stripped by the caterpillars. In this case, the worst scenario is that the spindle would die out and be replaced by neighbouring shrubs. Since that day I have seen several other cases of brown tail moth infestations: On the M11 near Duxford, the A14 near Fen Drayton, the A15 near Market Deeping and also near Oundle. It is certainly an exceptional year for these two caterpillars. As an update, I have revisited some of these sites in late July and I am glad to see that the shrubs have put out new shoots and will suffer no long term damage. Hairy caterpillars are an important food source for cuckoos, whose numbers have been declining in the UK for several years. Cuckoos appear to be unaffected by the irritating hairs, so it is important not to react hastily and spray infected hedges with pesticides. The hedge will recover and our cuckoos will benefit.

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Update June 2023.

The Spindle Ermine caterpillar is spreading its webs over all the spindle trees again this year. No sightings of Brown Tail caterpillars so far.

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