Nettle nursery

Here's one good reason to love your weeds: within this gauzy hammock a brood of caterpillars is developing, on their way to becoming the familiar Small Tortoiseshell butterflies that flit around our Buddleia bushes and come indoors to overwinter in the curtains.

The eggs are laid in large clutches on nettle plant and they spin themselves this protective veil in which to  live communally while feeding on the nettle leaves.  It's a protective bubble since whereas one single caterpillar makes an easy snack for a bird, a whole writhing cluster is a more challenging prospect.

The Small Tortoiseshell has suffered a drastic decline in Britain over the past 20 years, its population dropping about 80%. The reason may be the arrival (due to climate change) of a small parasitic fly, Sturmia bella, that lays its eggs on the nettle leaves where they are eaten by the butterfly larvae. Once ingested the eggs, Trojan horse-like, hatch into larvae that devour the caterpillars from inside. All nature is a precarious balancing act between the forces of survival and the forces of destruction; it only takes one factor to change, in this case, the temperature, for the balance to shift and an avalanche of change to follow.

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