Is This Sudden Cold Snap Bad News For Butterflies?

[Paul Harfield]

On Sunday I was burning out in the sun and yesterday we had snow here near Southampton and the last 2 nights were very frosty

This early butterfly season, spurred on by recent mild weather, is already in full swing particularly down here on the South Coast. What are the likely consequences for our butterflies of this sudden 'cold Snap' ? I am particularly thinking of those freshly laid eggs, freshly pupated larvae, freshly emerged adults and those just about to emerge. Is there a critical moment in the life cycle when butterflies are particularly at risk from a sudden drop in temperature?

I know nature can be fairly resilient, but are any of our butterfly species doomed because of this or are we perhaps going to experience a higher than normal number of aberrations? Any thoughts from the experts are appreciated

[Neil Hulme]

Hi Paul,

I don't claim to be an 'expert', but probably know sufficient to answer your query. It does look worrying when a walk through a young coppice coupe shows widespread 'cold-burning' of chestnut regrowth, bramble shoots and even drooping bracken! The frosts we've had lately have been harsh enough to blacken and wither delicate plant tissues.

But butterflies are much tougher than they look, at all stages in their life cycle, although some stages are tougher than others. We now know that the temperature-sensitive early stages of the Red Admiral can nowadays tolerate even the periodically harsh conditions of a British winter. Although sub-zero temperatures will still kill the majority, the development of some individuals will continue, over a greatly extended timescale. To go from egg to adult in six weeks under really warm conditions, but still manage to complete the journey over the six months including winter, demonstrates a remarkable level of plasticity in response to low temperature.

What we are seeing this spring is a far less challenging scenario, occurring over a much shorter period and affecting species which are much tougher than the Red Admiral - they've had plenty of time to adapt! The cold snap will simply put the brakes on the emergence of spring species, leading to drawn-out flight seasons, which isn't such a bad thing. Pearl-bordered Fritillary has been on the wing for some time now, and yet its season has barely started.

Those who have watched butterflies over many years will have seen this all before, most recently in 2010. Spring species emerged in very low numbers over an extended period, until the winds swung from the north to the southwest on 13 May. Butterfly numbers exploded, relatively late during what we consider their current flight seasons. That said, the arrested development of pupae, in response to low temperature, does have its limits. Beyond a tipping point, mortality rate will start to rise, due to factors such as desiccation.

More severe, unseasonal weather (and I mean really severe) can, however, be utterly devastating. Research I conducted for The Butterflies of Sussex https://www.naturebureau.co.uk/bookshop ... sex-detail suggests that the winter of 1947 (the longest period of snow cover during the 20th century) and artic summers of 1954 (frosts in July) and 1956, which occurred immediately prior to the compounding effects of myxomatosis (overgrowth of swards following introduction of the disease in 1953) had a massive impact of the fortunes of a suite of warmth-dependent species. In some cases this took them more than 30 years to recover from; in other cases, such as the chalk-bound race of Grayling, they never did. I believe that the period 1947 - 1956 represents a major watershed for British butterflies.

Will we see a high incidence of environmentally-triggered aberrants? There are a couple of possible contenders, but I'd like to see some wild temperature swings in late May. Bring on the black White Admirals and purple Purple Emperors!

BWs, Neil

[bugboy]

I was going to reply to say I didn't think we have too much to worry about but I think Neil has pretty much covered all my thoughts in much greater detail than I intended to .

I think the main thing to remember is that the species that we have on our little islands are the select few that over the course of time since the last ice age are the ones that CAN cope with British weather and climate. Other species most likely came and went as our climate waxed and waned leaving us with the 60 species we have today (and of course this waxing and waning will continue).

For me a greater worry in the short term this year is the lack of rain, particularly down here in the south east.

[Lee Hurrell]

An excellent (and reassuring) response from Neil. I think that being an island has its pros and cons, weather and catastrophic event wise.

I would agree with Buggy; at Noar Hill and Chiddingfold Forest last weekend both locations were parched. We have had around one fifth of the rain we would normally receive in the south-east so far during April, according to BBC weather one day recently. I hope the last couple of days have helped.

Best wishes,

Lee

[Susie]

I'm hoping we're going to get a bumper crop of abs

[Tony Moore]

A bit off message, but our bad Spring/Summers coincide with poor wine vintages, particularly in Bordeaux. . So, no butterflies - stay off the Claret...

Tony M. (hic!)

[Paul Harfield]

Thanks all for your comments especially Neil for that concise explanation, many thanks. Hopefully there will not be another 1947 any time soon.