The sap is rising and all around the countryside things are springing into leaf. Fresh green leaves, often miniature versions still to expand to their full size, see a welcome return of green hues to the landscape. The stark, two-dimensional forms of branches are now clothed and the dry soil beneath shaded by an expanding canopy of life. These new leaves will power this season’s growth, enabling many trees and other plants to lay down reserves that will see them through the distant winter.
This flush of green serves another purpose and is already being eyed by hungry bugs that will chomp, munch and slurp their way through its plump cells. The caterpillars of various moths will be among the most numerous of these eager herbivores. While some will live on the surface, trimming back the fresh growth, other tunnel their way through the soft tissue leaving behind them characteristic ‘leaf-mines’ full of frass (caterpillar droppings)! Caterpillars are not the only creatures to mine the leaves; various sawflies, flies and beetles also make a living in this manner.
Some of these mines will be familiar enough to regular readers of these columns. The Horse Chestnut Leaf Miner has made the headlines on numerous occasions since it first reached our shores. The sheer size of its population on individual trees has turned the entire canopy a rusty brown and there have been calls that ‘something should be done’. It might well be that the population of this particular leaf miner settles down to a more respectable level over time, in much the same way as was the case with the Firethorn Leaf Miner just a few years ago. The mines made by many of the small leaf mining moths tend to be all that we see of the moth, so small are they in size. However, these diminutive creatures, just a couple of millimetres in length, are some of the most beautifully marked and patterned moths, with tufty golds, shining purples and wispy whites.
Some of the other leaf feeders are equally impressive but many adopt more subtle tones, attempting to blend in with their surroundings and avoid the unwelcome attentions of would be predators. Nevertheless, the vast number of leaf feeding invertebrates is a food resource that is fully exploited by nesting birds. Resident tits and newly arrived warblers will feast on this spring bounty, using it to fuel their own breeding attempts. So tightly are some of these birds tied into their invertebrate prey that their breeding success is dependent upon them matching the timing of the peak in their chicks’ growth with the peak in caterpillar abundance. This, in turn, is linked to the timing of bud burst and that first flush of green.