The Small Tortoiseshell

Description

One of my favourite butterflies, this usually gives the impression of a dull orange medium sized butterfly, sometimes confused, by me at least, with the Comma. 

Distribution

Found throughout the British Isles, it is seen on field paths and nectaring in gardens in both Hadlow and Golden Green.


Life cycle

Small Tortoiseshells overwinter in sheltered spots such as sheds and outhouses, so are one of the first butterflies to be seen in spring. They seem to have rather hairy bodies, with "manes" of long hair over the inner parts of the upper-wing next to the body which might perhaps help to keep them warm on colder days. In most of the country, these overwintering adults mate and then lay eggs in May which produce a fresh adult generation in June/July which in turn lay eggs in July/August which produce the "second generation" of that year which are on the wing from September/October onwards and which will hibernate overwinter and reappear to fly in the spring of the following year. In the north of the UK, there is only one generation, of new adults each year, which last until the following summer. 

There is some Swedish research that suggests that the larval stage is unaffected by daylength determining the choice of the adults either mating or of entering diapause. At the adult stage there is an impact: there are some individual adults whose choice of mating or diapause is determined by daylength, but there are others which are non-responsive. However, this pattern of larval insensitivity but adult sensitivity to daylength is not true of many other species that have been studied.

The eggs are laid on Common and Annual Nettle leaves in large groups, producing black golden-spotted caterpillars that feed colonially.

Here is a Small Tortoiseshell casting a long shadow. This photo is of a June adult, only moderately worn and in pretty good condition, so should, I think, be one the early individuals of the first summer generation produced this year that will breed and then die within a month or two, giving rise to the second, over-wintering generation.

Now this is another, seen along the Bourne Valley on the same day, but this one is in near pristine condition. The blue flashes near the wing edges and the double lines on the wing edges themselves are much clearer, and the thorax/abdomen shows almost zero damage!

Bourne Valley, 12-06-2014

Oddities



Predators and parasites

There is a parasitic fly, Sturmia bella, found on the continent and the southern parts of Britain that may be impacting on population numbers of the Small Tortoiseshell in recent years.