Why is it .....

[Pauline]

..... that butterflies seem to be the last insect to become active in this dreary weather? Whilst waiting for the sun to emerge (to increase the temperature) it would seem that just about every other bee, fly and insect is on the move - except the butterflies. I have considered colour, heat absorbtion, body size but none of these seems to fit. has anybody got any ideas????

P.

[Wurzel]

I've noticed a similar thing. Generally Carder bees and flies and then other bumbles bees will appear followed by the smaller bees. I think that it's to do with the flight temperature of 13 degrees? Some butterflies refuse to fly unless it's even wearmer than that - such as Silver Spotted Skipper.

Have a goodun

Wurzel

[dilettante]

I can't remember who posted this link before, but this is how bumblebees are able to fly in lower temparatures:

http://www.bumblebee.org/bodyTempReg.htm

[Pauline]

Fascinating stuff! I'd always assumed insects were all cold-blooded! Well, we live and learn Presumably other species have their own (similar?) mechanisms to deal with low temps. Thanks for reply Dilettante.

[Susie]

I must have read that article before but it is fascinating reading it again as I don't recall knowing that bumblebees have a brood patch in the same way that birds do. That'll be my fascinating fact for today.

It's worth remembering that if you see a grounded queen bee during the early spring it is worth putting her up somewhere high as sometimes they have difficulty taking off when it is cold and being at height can help get them flying.

Moths can be seen "shivering" to get their body temperature up too. Some moths that fly during the winter can be particularly hairy to keep them warm.

[David M]

You could widen this discussion by questioning why some butterflies are more tolerant of low temperatures than others.

Ringlets, Meadow Browns and Speckled Woods are all famous for being active in dull, cool weather (and given they're all dark perhaps that's not surprising). Grizzled Skippers seem fine at lowish temperatures too for perhaps the same reason.

Yet there are others that seem to demand much higher temperatures in order to become active, e.g. many of the Blues and Hairstreaks, and then there are others such as Lulworth Skipper which cling on in only the balmiest, best protected areas of the south coast.

[Padfield]

Many butterflies have large wings and efficient, almost effortless flight. While this is excellent for energy conservation it may mean their flight muscles generate little heat while they are on the move. In contrast, flies have a much smaller wing area to body mass ratio and buzz around, perhaps maintaining heat production on the wing. Even small, buzzy butterflies like grizzled skippers have a larger wing area to body mass ratio than many other insects.

Still thinking of energy: generating heat is obviously costly. A creature that generates its own heat must either eat more or live less long than another that relies on environmental heat. Maybe those species that won't fly until it is really warm have gone down the evolutionary path of living longer, more productive lives, without having to spend so much time refuelling.

All pure speculation, as ever. There are doubtless myriads of different factors affecting which species fly at which temperatures.

Guy

[Pauline]

Thanks Guy, David. Plenty of food for thought then.