Small tortoiseshell butterflies

Posted: Wednesday 8 May 2013
by Richard Jones

It’s been fascinating to follow the tweets of butterfly enthusiasts as they marked the arrival of warm weather during the last fortnight.

Small tortoiseshell

It’s been fascinating to follow the tweets of butterfly enthusiasts as they marked the arrival of warm weather during the last fortnight, by discoveries of green hairstreaks, Duke of Burgundy Fritillaries and even some large tortoiseshells in the Isle of Wight. I can’t match any of these (not a ‘real’ lepidopterist I suppose). But my heart went all aflutter 10 days ago when I saw a small tortoiseshell.

It’s a bright and pretty species, for sure, but it’s also arguably Britain’s commonest and most widespread butterfly. Why then, I hear you ask, should it get a hardened professional like myself all unnecessary? Because this was the first small tortoiseshell I’ve seen in three years.

Tales of butterfly decline are depressingly commonplace nowadays, but the discovery in 2011 that small tortoiseshell numbers had gone down by 68% in 10 years was pretty shocking. It has always been received wisdom that common generalist ‘garden’ species, like the small tort, were protected from some of the frightening declines of specialist species. Being adaptable, unfussy eaters, often strong and exploratory fliers, they could found new colonies (or renew old ones) easily, keep the gene pool nice and deep, and escape the concentrated attentions of treacherous parasites and diseases. On the other hand, scarce specialist species become more and more isolated and genetically vulnerable, tend to have sedentary habits, and are thus more prone to colony destruction, and less able to repopulate.

The arrival of a new parasitoid fly, Sturmia bella, in 1998 has been mooted as part of the butterfly’s downturn. Within the same decade of the butterfly’s decline, the fly (which specialises in parasitising small tortoiseshell, comma and peacock butterflies) spread across the whole of England. It doesn’t appear to be quite that straightforward, though. Small tortoiseshell numbers went down in places where the parasitoid is currently unknown, and also in Europe where the fly is not a ‘new’ threat to the butterfly.

In the past, the small tort’s numbers have oscillated before. Some years were good, others bad. It may be that increasingly intensive recording is telling us now just how much these changes are, by giving us hard statistics. It seems the butterfly’s numbers tend to crash after a hot dry summer. Since 2012’s summer was, er, rather wet, perhaps it was the much needed respite that the butterfly needed to start a recovery.

Anyway, I was very excited when I saw one. A few days later I saw another. I tweeted about them both.

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oldchippy 09/05/2013 at 14:03

Today I saw my first swift,Saturday I saw some swallows, last week I saw my first Tortoiseshell butterflies in the park,I have seen some orange butterflies and birds are returning.

flowering rose 09/05/2013 at 14:25

I saw in the garden,peacock butterfly,yellow brimstone,a skipper,a little blue one and a brown butterfly .We use to have masses of butterflies on the buddleia but now even when things are good I am lucky to see more than one of each species.I try to grow things they like and a few weeds in spare bit of the garden.The birds are back,swifts ,goldfinch,and all the others I thought were gone.

david 12 11/10/2013 at 20:38

This year, after a few years without many butterflies, they have returned to my garden. The usual common types + quite a few small tortoise shells and what I thought was a white admiral near the honeysuckle, it was moving fast.
What I was puzzled about was the dearth of hoverflies, cardinal beetles and wide range of flying insects, that we are usually awash with. The same plants grew as usual. I can only surmise that the few days of icy winds that killed some of my plants may have done for hibernating insects. Swings and roundabouts !