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.
