There are thousands of species of invertebrates that overwinter in the leaf litter below our gardens’ trees and shrubs.
There are creatures that live part of their life cycle attached to the leaves: the mature larvae of silk button gall wasps and spangle gall wasps spend the winter in their galls, safely out of sight in the leaf litter.
Silk button galls on oak leaves and knopper galls on acorns.
There are whole micro-ecosystems in the knopper galls that fall from oak trees into the autumn leaves. Beside the pupa of the knopper gall wasp herself (they are all female at this stage of their life cycle), there are other micro-inhabitants such as cynipid wasps which lay their eggs in the ready-made gall where their larvae can feed on the gall’s tissues. Then there are the parasitoids: chalcid and ichneumon wasps which inject their eggs into the gall wasp larvae to feed on them. If you tidy away the galls and the leaf litter and burn it all, you destroy the whole community.
There are the pupae of the moths and flies, whose larvae fed in the tree during the summer but came down to the ground to pupate as autumn set in, relying on the leaf fall to hide them from predators and shelter them from the cold. Elephant hawk moths and scorpion flies spend their pupal stages hidden below the dead leaves. Remove the leaf litter and you have removed their protection.
Elephant hawk moth and scorpion fly
Let’s let the leaves lie: let them pile up in corners on our patios and lawns, providing shelter for invertebrates, vital components at the bottom of so many food chains. At this critical moment of our enviromental emergency, the state of our lawns and our neatly swept patios is almost completely insignificant but a network of urban gardens carefully maintained for whole ecosystems, whole food chains, could be very significant indeed.