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. 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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Coppicing Season Ends and Pat Starts Building

Birchanger wood
Birchanger Wood warden Pat Forrest building a new wood store in our compound

The coppicing season has come to an end at Birchanger Wood. Volunteers have laboured hard over the winter to cut back trees to allow light onto the woodland floor, boosting the flora and helping to support biodiversity.

While it may seem counterintuitive to cut down trees for the sake of woodland conservation, coppicing is an age-old practice of harvesting trees for wood products – baskets, beanpoles, walking sticks, arbours, thatching, fences, charcoal and firewood. The practice of coppicing goes back to a time when society was heavily dependent on wood and woodlands were cared for due to their economic importance.

Many bird species rely on insects as a source of food and insects benefit from the flowers that flourish when the woodland floor gets more sunlight, unimpeded by the dense canopy of mature trees.

The trees themselves are not harmed and if they are protected from browsing animals such as rabbits and deer, they will grow back healthy – often with a longer lifespan than if they were left to grow as standards. However, the trees and flora can only thrive if walkers, cyclists and dogs keep to the paths.

In line with a management plan devised by conservation experts and overseen by our warden Pat Forrest, Birchanger Wood Trust is pursuing this time-honoured method of woodland management with sales of firewood from coppicing helping to sustain our work.

We are now boosting our capacity to coppice larger areas by training long-standing volunteers in safe chainsaw use and building a covered wood store in our secure compound. The store will improve the quality of firewood, which was being stored under canvass where it was more open to the elements.

We look forward to another summer watching our woodland benefit from continued management and developing a legacy for future generations.

We have a packed series of events led by local science educator and conservationist Jono Forgham – visit our events page for more details.