Is the Tortoise Slowing Decline?

I was sad to recently read, that the Small Tortoiseshell Butterfly Aglais urticae - which I plead guilty to having taken for granted, as an ever-present visitor to our gardens and hedgerows each Summer - has in recent years been suffering a significant reduction in numbers in Britain (particularly in the South)

Small Tortoiseshell Butterfly Aglais urticae

One of the possible reasons for this decline is thought to be a parasitic fly, Sturmia bella, which is common on the Continent but had not been recorded in Britain until 1998, however, it is now being recorded in many parts of Britain and particularly in the South. Global warming will no doubt be blamed as a likely reason for the flies immigrating to our shores.

The fly lays its eggs on the caterpillars’ foodplant (often nettles) and the Butterfly larvae then ingest the tiny eggs as they munch their way through the leaves. A grizzly death ensues, as the fly grubs emerge and feed on the insides of their host, although being careful to avoid eating the vital organs, until they are ready to break-out from either the fully-grown larva or pupa, at which point the host dies.

How did I ever take these for granted?

- the colours are truly beautiful

 This fly also attacks related species, such as the Peacock and Red Admiral, but it seems that unfortunately for the Small Tortoiseshell, it’s life cycle is better attuned to that of the fly and is more susceptible to attack.

  

Also at risk the Peacock Butterfly

On a more positive note - and whilst I fully accept that one man’s observations do not a scientific study make - I can’t help thinking that this summer seems to be a particularly good year for many species of Butterfly - including plenty of Small Tortoiseshells around these here parts. I can only guess and hope, that this year, the long, warm, dry weather may have helped more Butterflies to have hatched and survived.

The paradox of course being, that a long warm British summer may also encourage greater numbers of the parasitic fly.