Small Tortoiseshell (Aglais urticae) - Devon, UK
Canon 300mm F4 IS plus 1.4 x Extender and Canon Extension Tube EF 25 II
Fill Flash -2
AV Mode, Evaluative Metering dialed to -2/3
Text adapted from - http://www.ukbutterflies.co.uk/species.php?vernacular_name=Small%20Tortoiseshell
The Small Tortoiseshell was not long ago regarded as one of Britain's most familiar and common butterflies, but in recent years has shown signs of decline. It has, however, always been subject to dramatic fluctuations in abundance from year to year. In some years the butterfly can be extremely scarce, but in others it can be a very common and abundant species.
These cycles of abundance are believed to be linked to spring and early summer temperatures, which affect both the butterfly, and its larval parasitoids. Recent evidence also suggests that common wasps are major predators of the larvae, and it is likely that in years when wasps are abundant, Small Tortoiseshell numbers are greatly depleted.
The butterfly gets its vernacular name from the pattern on the underside of the wings, which is said to resemble that of a tortoise shell. The scientific name, urticae, refers to the stinging nettles on which the caterpillar feeds.
The main foodplants are Common Nettle (Urtica dioica) and Small Nettle (Urtica urens).
This is one of our most widespread resident species. It is highly mobile, and can be seen in almost any habitat, including woodlands, grasslands, heaths, gardens, country lanes, and town centres. I have even seen it at the peaks of mountains in Scotland and the Lake District. The butterfly is perhaps commonest however on farmland, where stinging nettles are profuse, and where there are farm outbuildings where it can hibernate as an adult.
In April, female Small Tortoiseshells are often seen flying around young nettle patches, where they lay their eggs in large heaps on the underside of the nettle leaves. At this time of year the butterflies choose nettles that grow in warm sheltered sites, such as at the bottom of south-facing hillsides, along dykes and riverbanks, near hedgerows, and along disused railway cuttings. The summer brood is less fussy about the situation, and will lay on nettle patches in gardens, in woodland glades and rides, and on exposed hilltops; but the butterflies always favour young nettles, and rarely oviposit on the tougher leaves of old growth.
Immediately after hatching, the larvae spin a communal silk web around the terminal leaves of the nettles. They shelter within the web overnight, or in inclement weather conditions, and feed avidly whenever the sun shines.
When young, they can easily be mistaken for the caterpillars of the Peacock, but Small Tortoiseshell larvae are paler, and even when quite small, it is usually possible to discern pale lines running along their backs. The larvae split up into smaller groups, and spin new webs after each moult, but become solitary when they enter the final instar. By this time they are a dull blackish colour, spiky, and have 2 prominent yellow lines running along their backs. The older larvae can often be seen curled in a J shaped posture, resting on the upperside of nettle leaves, and if disturbed will curl into a tight circle, and drop to the ground.