But nothing prepared us for what we found a few weeks later at the Broad Arboretum at the Earth Trust. As we walked through the trees, we came across a whole section where tree after tree had been completely wrapped in silk. It genuinely looked like Halloween had arrived in the middle of summer. The branches shimmered white in the sunshine, with thousands of caterpillars moving beneath the webbing.

It was one of the most extraordinary wildlife spectacles we've seen. At first glance, it can look as though the trees are dying, but they're usually much tougher than they appear. The caterpillars feed on the leaves of trees such as bird cherry, spindle and hawthorn, depending on the species of ermine moth. Although the trees can look completely stripped of leaves for a while, they almost always recover and produce fresh growth later in the season.

The silk itself is another clever adaptation. By living together inside one enormous web, the caterpillars gain protection from many predators and can move safely between leaves without exposing themselves. It's like building one giant shared tent over the whole tree.