A Case of Too Many Very Hungry Caterpillars

Some visitors to Birchanger Wood have remarked on the massive number of tiny green caterpillars. Unfortunately, this Spring we are facing a massive invasion of winter moth caterpillars, which are chomping through young leaves on our trees. Their hatching is timed to coincide with the budding of oak leaves, their favourite dish. They also feast on maple, birch, hornbeam, hazel and beech – all the tree species that can be found at Birchanger Wood. The large number of caterpillars is leading to the defoliation of many trees.

Hatching is determined by temperature. The moths are adjusting to climate change through selection with the larvae of the most adjusted eggs thriving. As the climate is changing in winter and spring, the winter moth is hatching earlier and earlier to synchronise with their main food sources. If the caterpillars hatch before the trees bud, then they will have no food source and will starve.

There is little we can do about the blight but hope that the birds will take advantage of this plentiful food source. Tits are known to predate the winter moth caterpillar and will feed them to their young. However, this will only work well if the peak wood moth caterpillar population coincides with the hatching of the tits’ eggs. Scientists have found that the birds are less able to adjust to the earlier peaking of caterpillar populations, which means they are often unable to take full advantage of the higher caterpillar population.

Research has found a mismatch emerging between caterpillar hatching and the hatching of woodland birds. Dr Karl Evans, from the University of Sheffield’s Department of Animal and Plant Sciences, told The Telegraph: “Our work suggests that as springs warm in the future less food is likely to be available for the chicks of insectivorous woodland birds unless evolution changes their timing of breeding.”

So, the problem isn’t going to go away easily. We can only hope that this is a bad year due to specific weather trends this Spring and that the trees will continue to bud new leaves after the caterpillars pupate.

If you are interested in moth identification and learning more about moth species in Birchanger Wood, please visit our events page.

The pictures on this page were taken today in Birchanger Wood.

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