Insects of deciduous woodlands
The insect and other invertebrate life in deciduous habitats occurs in a bewildering array of forms. Every source of organic matter supports some kind of invertebrate, whether in thedeep below the litter or on the topmost bud. These diminutive animals not only exist in a great diversity of forms: any one species can be extremely numerous. In some years the canopy of a large oak may accommodate about a quarter of a million caterpillars of the winter moth and these, in consort with, for example, green oak moth, mottled umber and spring usher larvae, may emerge from the buds in spring to defoliate their hosts almost entirely. Most deciduous trees defend themselves against such wholesale attack by producing tannins and other toxic compounds which make the leaves harder to digest. Some counter measure is crucial, for leaves are assailed from within and without-they are bitten and chewed by caterpillars and adult weevils, mined by moth, fly and weevil larvae, sucked by bugs and disfigured, sometimes grossly, by gall-forming midges, mites and wasps.
Theof most trees are wind pollinated, but some, like the sycamore, maple and lime, are regularly visited by pollinating insects, particularly bees, which therefore provide a valuable service. Much more prolific sources of pollen and nectar, however, are provided by the shrubs and flowering plants lower down, notably honeysuckle and bramble, which some moths and butterflies find especially attractive. Later in the year many insects make a final visit to feed on rotting fruits and tree sap. Inside the trunk, another community of insects is busy, especially at any vulnerable points of decay. As many as 450 species of insects have been found to thrive in decaying wood. The first invaders are often specialist bark beetles whose ‘softening up’ process paves the way for woodlice, millipedes, centipedes, spiders, earwigs and flies. Later still, ants, bees and wasps may colonize the labyrinthine interior of the stricken timber.
Many of these invertebrates exist equally well in the leaf litter, the woodland ‘basement store’ of organic matter. Here earthworms, mites and springtails also abound, breaking down the waste products of everything above them-to the profound benefit of the woodland.