Impact on butterflies of a mild winter

[David M]

At work today, I was discussing with my colleagues how I'd only needed to de-ice my car twice so far this winter (I leave for work before 7am and -1.5C is the lowest my in-car thermometer has read thus far).

There's no sign of a freeze until the second week in January at the earliest (if at all), so I'm prone to wonder what sort of effect an unduly mild winter would have on next year's crop of butterflies.

I guess there'll be heaps of Red Admirals given that they were present in large numbers during the warm autumn and nothing will have happened to make a major impact on that. However, what will the implications be for other species? Milder winter weather presumably causes less mortality to overwintering butterfly stages, but it also renders predators largely harm-free too. I'm still getting good numbers of slugs and snails on my garden wall at night so I suspect there will also be wasps, spiders, etc that have been equally immune to the elements and will consequently start 2012 with far greater numbers than was true in 2011.

I'm almost praying for a cold snap now as I believe it has a revitalising effect in some ways, but if one isn't forthcoming over the next 4 weeks then we're going to be in a position that represents almost the polar opposite to last year where freezing conditions set in abnormally early and remained unchecked until early January.

[essexbuzzard]

Im inclined to think that a mild winter is bad news for butterflies. The pests,parasitoids and fungal rots that attack many species fail to be killed off,leading to greater numbers next year.
It is thought by many that our damp,mild winters prevent many european species from becoming established. The Camberwell Beauty,for example,is known to prone to fungal rots over winter and,even in Europe,tends to winter in dry,cold areas. Many species survive much further north than Britain,in Scandinavia,suggesting cold weather is in fact a benefit, suprising though it seems.
However,it's only December,and we may yet get a proper winter.
It would be interesting to get other opinions on this-am i right?
Regards,
Mark.

[Gibster]

Hi Mark, I think you are spot on regards parasatoids, fungal attacks etc.

Of course a mild winter will provide a more accessible food supply to woodland birds, meaning the local Long-tailed Tits hopefully won't decimate the overwintering Purple Hairstreak eggs again. We had a poor PH year at my patch Epsom Common. I had a quick look for eggs yesterday without any success.

Cheers,

Gibster.

[David M]

Strange that, Seth. Purple Hairstreaks were almost ubiquitous for me this summer. For a three week period they turned up practically everywhere I went - often in numbers.

[Dave McCormick]

Im inclined to think that a mild winter is bad news for butterflies. The pests,parasitoids and fungal rots that attack many species fail to be killed off,leading to greater numbers next year.
It is thought by many that our damp,mild winters prevent many european species from becoming established. The Camberwell Beauty,for example,is known to prone to fungal rots over winter and,even in Europe,tends to winter in dry,cold areas. Many species survive much further north than Britain,in Scandinavia,suggesting cold weather is in fact a benefit, suprising though it seems.
However,it's only December,and we may yet get a proper winter.
It would be interesting to get other opinions on this-am i right?
Regards,
Mark.

A cold winter is beneficial as some species like Camberwell beauty. If they don't get one they could wake up on the mild days, fly around, waste energy and end up running out of energy and fat reserves and dying before there is flowers and places they are able feed in Spring. On mild days you may see the odd butterfly around, but with nothing to feed on, they just lose energy doing so, staying cold enough to make them stay in hibernation is the best way for them to have enough fat reserves to make it until its warm enough and there is flowers and then they can safely wake up, fly off to find places to feed. This is probably why the Camberwell Beauty may not survive in the UK overwinter since these winters are becoming too mild and they wouldn't successfully make it to Spring.

The weather this winter so far, sad to say, you'd lose some adult hibernating butterflies this way, lack of food and using energy, they'd be lucky to make it to the warmer weather and when they can feed. It will be interesting to see the numbers of Red Admiral, Comma, Peacock and Small Tortoiseshell next Spring.