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Hi,
What will be the impact on butterflies of this sudden change of weather from hot, sunny April, to a cold, wet May? In particular, two species (that I'm not allowed to mention here) had just begun to emerge a couple of weeks ago. I have never seen them and didn't get chance to get out to try for them before the weather changed. So will their emergence continue when the weather improves or will it all be over until next year?
I'm assuming that if the weather gets better then there will be little impact on those species due to emerge later in the year.
Cheers,
Robin

I was told that due to a wettish May, we will see a milder summer than last year. What I was told:

A fine April is no guarantee of a warm summer (1974 and 1980 were very disappointing, though after a warm April in 2003 the summer was also warm) and after a very warm summer in 2006 I think it is unlikely it will be repeated, although of course weather predictions are always risky.

Robin Turner wrote:Hi,
What will be the impact on butterflies of this sudden change of weather from hot, sunny April, to a cold, wet May? In particular, two species (that I'm not allowed to mention here) had just begun to emerge a couple of weeks ago. I have never seen them and didn't get chance to get out to try for them before the weather changed. So will their emergence continue when the weather improves or will it all be over until next year?
I'm assuming that if the weather gets better then there will be little impact on those species due to emerge later in the year.
Cheers,
Robin

An excellent question Robin.

I think the impact will (obviously!) be species dependent. For all of those species that have managed to get through their flight period, or those yet to start their flight period (even if the larvae have fed up more quickly than usual) I'm not that concerned. The cooler / damper weather will slow down their emergence.

I think the species most threatened species will be those that are just reaching their peak, with adults on the wing and many emerging imminently. For example, this would encompass certain populations of Marsh Fritillary and Adonis Blue down south. I say this because those adults that have already emerged may have suffered in the miserable conditions of late, and may not survive long enough to pair up with those yet to emerge.

Just a thought.

Cheers,

- Pete

On this, is it a bit late to start seeing Small Tortoiseshell caterpillars young? I only saw the first first or seond instar small tortoiseshell caterpillars a week ago and I saw a few small tortoiseshell still courting at beginning of May.

My first thoughts when i learnt that, Marsh Frits only live for a few days, as a flying adult, were - What if the weather turns bad for a few days, as it has been of late. Surely evolution has not been too clever here

Gruditch

I think they live considerably longer if they don't expend their energy by flying. So they should be able to outlive at least short spells of bad weather.

I was very concerned last year when heavy snow fell on 31st May (after light snow on 30th). Here is my garden that day:

.

It continued snowing on 1st June and snow lay on the ground on 2nd June.

HOWEVER, my concern seems to have been misplaced: as soon as the snow melted, everything started flying again and 2006 was an excellent season. 2007 has been even better, with no diminution at all in the butterflies snowed on last year.

What of longer periods of cold or wet? As others have pointed out, butterflies go torpid and, being cold blooded, metabolise much more slowly in the cold, so their energy reserves remain high if they don't fly (though they do still respire and don't go into a true hibernative state). We often get several weeks of mist and cold in May here in the mountains and this seems to have little or no effect on our butterflies.

I suspect the biggest danger would be periods of warm, overcast or wet weather, when they would respire at a higher rate and thus run down their reserves more quickly, without flying and mating &c. As Pete says, this would affect most seriously those species at the peak of their flight period. However, my impression is that when such weather ends, the emergence of the remaining butterflies from their chrysalids is synchronised and mating opportunities are optimised.

In short, while adverse weather conditions do certainly have an impact on butterfly populations, I believe they are as nothing compared with the impact human activity has on those populations!! Insects have survived wet Mays for millions of years, but the draining of fens, tidying up of hedgerows, intensification of agriculture and creeping urbanisation are something evolution has tragically failed to prepare them for.

Guy

The biggest danger would be that the heat would cause Estivation (Himbernation through peorids that are too hot for creature) and the adults would appear on the wing again later in the year and next years broods would be out of proper flight time.

Also, when would you be likley to see orange-tip larvae? I check a couple of weeks ago and saw eggs. Check last weekend and still saw eggs. Would colder weather impact the caterpillars emergence/growth too?