Sunday 15 September 2019

Speckled Wood butterfly has unique life cycle


IT HASN'T been a great season so far for butterflies but when weather conditions are conducive the Speckled Wood is one of the most common species on the wing at this time of year.

It is a smallish butterfly and the ground colour of its upper surface is brown speckled with yellow patches. The brown ground colour can vary from pale to dark and the yellow speckles can be so pale as to appear almost off-white or to be such a dark shade of yellow as to appear almost orange.

As the 'wood' part of its name tells us it is a woodland species that favours the dappled shade found under trees. Hedgerows can represent linear strips of woodland and it is along hedgerows and around shrubs in parks and large gardens that the insect is most often seen.

In addition to its yellow patches, the Speckled Wood has black eye-spots each with a white pupil. To set it off each eye-spot is located in a yellow patch. There are eight eye spots in all; one on each forewing and three in a line near the hind margin of each hind wing. No other butterfly has that particular combination of markings so the species cannot be confused with any other insect.

The Speckled Wood is unique among butterflies in another way: it can overwinter either as a caterpillar or a pupa. That peculiarity of its life cycle means that in springtime some caterpillars are only entering the pupal stage whereas some pupae are producing adult butterflies.

The upshot of that is that there is an overlap of generations resulting in some representatives of the species being on the wing almost continually from springtime to late autumn. Adults suck nectar from a wide range of flowers; caterpillars munch on the leaves of wild grasses.

A combination of tall woody plants, bright sunlight, dappled shade and still warm air are the insects preferred habitat. Males are territorial; they stake a claim on a suitable patch and either sunbathe on a leaf to show themselves off or dance in the air to attract passing females.

Passing males are unwelcome. If a rival male attempts to steal its territory the defending male attacks and sees off its rival. It is not unusual at this time of year to see two males locked in aerial combat spiralling upwards as they fight for a prize patch of hedgerow bathed in dappled shade.

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