Tuesday, 7 April 2015

Norfolk butterflies in spring

Nick Acheson, NWT

Peacock butterfly photo by Pat Adams
Among the most heart-warming signs that winter is dying and spring is underway is the sight of a butterfly on a bright, mild day. Through the spring, summer and autumn Norfolk’s butterflies come in waves of species; and the date of emergence of adults of each species is closely related to its life cycle and, in particular, the state in which it spends the winter. The first wave of species to be seen, in early spring or even on mild days during winter, is of those which overwinter as adults, the technical term for an adult insect being imago. Some members of the Nymphalid family, the peacock, small tortoiseshell, comma and, increasingly, red admiral, and one member of the Pierid family, the brimstone, adopt this strategy.

Orange tip, photo by Ray Jones
The first to appear of the second wave of species –  those which have overwintered as pupae – is usually the orange-tip; the male a startling flash of colour over a wet meadow. He is quickly followed by three closely-related species in the Pieridae, the large, small and green-veined whites, which have also overwintered as pupae. At the same time green hairstreaks are busy around gorse, grizzled skippers in unimproved grassland, and holly blues in gardens and along hedgerows. The latest to emerge of the species which overwinter in this form is the swallowtail.

Meadow brown, photo by Maurice Funnell
While these early species are flying as adults, those which overwinter as caterpillars are pupating in spring, in readiness for their emergence as adults in summer. These include most of our familiar grassland species: browns (Nymphalidae), skippers (Hesperidae) and blues (Lycaenidae), though not all blues are blue. Surprisingly, Nymphalid species such as meadow browns, ringlets, graylings and gatekeepers may have fed on grasses as caterpillars all through winter. A few woodland species have also overwintered as caterpillars: white admirals on honeysuckle and silver-washed fritillaries (very recent re-colonists of Norfolk) on violets on the woodland floor.

Silver-studded blue, photo by David Tottman
Though it seems counterintuitive, very few species spend the winter in the most indestructible, hardest-to-find stage of a butterfly’s life cycle: the egg. Most are small, high summer butterflies which have time in the spring to hatch, feed as caterpillars to full size, and briefly pupate before emerging as adults in summer. The Norfolk species which use this strategy are the purple and white-letter hairstreaks, treetop butterflies of oak and elm respectively; the Essex skipper, discovered as recently as 1889; and the chalkhill and silver-studded blues, both of whose caterpillars are protected, to differing degrees, by ants, in return for sweet secretions.

Just one species, the speckled wood, is an exception, overwintering as either a caterpillar or a pupa. This flexibility may account for the speed with which it has spread north through Norfolk in living memory, aided perhaps by climate change.

As you see each butterfly species this spring and summer, spare a thought for the miracles of biology it has been through to reach maturity and brighten our Norfolk landscape as an adult.  

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