Glasgow & SW Scotland Butterflies

Glasgow & SW Scotland Branch Website

March 21, 2010

How late will butterflies and moths be this spring?

Filed under: Butterflies, Moths — Andrew Masterman @ 1:47 pm

After the cold winter of 2009/10, it is likely that we will have to wait rather longer to see butterflies and moths on the wing this year than in recent years when spring phenology has been advanced.

Here are some stats on the winter. The Met Office areal series for Scotland which goes back to 1914 has 2009/10 as the second coldest winter on record being only  0.1 C warmer than 1962/63 with a mean winter temperature of 0.3 C.

There are some temperature data for sites in Scotland which go back much further than 1914 and the longest series is for Edinburgh going back to 1764 which was compiled by Robert Mossman.  He created a record for Edinburgh for the peroid 1764-1896 by assembling several datasets recorded in the Edinburgh area. This Edinburgh temperature record can be continued up to date using the Edinburgh Observatory record up to 1960, the Edinburgh Airport data from 1961 to 1999 and data from Leuchars, Fife from 2000.

Here is a graph showing this temperature record back to winter 1764/1765.

Mean winter temperature at Edinburgh 1765-2010

Mean winter temperature at Edinburgh 1765-2010

And here are the rankings:

Winter Mean Temp Ranking
1780 0.1 1
1879 0.2 2
1814 0.5 3
1963 0.7 4
1838 1.0 5=
1860 1.0 5=
1823 1.0 5=
1795 1.1 6
1881 1.2 7
1774 1.4 8=
1947 1.4 8=
1820 1.4 8=
1895 1.5 9=
1784 1.5 9=
1766 1.6 10=
2010 1.6 10=
1816 1.7 11=
1785 1.7 11=
1845 1.7 11=
1776 1.7 11=
1979 1.7 11=
1808 1.8 12=

Using data for Leuchars which is outside Edinburgh, the mean winter temp  for 2009/10 was 1.6 C giving a ranking of 10th equal with 14 colder winters since records began in 1765.

I did find data for Edinburgh Gogorbank online back to 2003 but as the Airport closed in 1999, use of this site which is better in terms of siting than Leuchars in the graph above would leave a gap.

But I compare Leuchars and Edinburgh data for winter 2009/10 below:

                         Dec         Jan              Feb

Leuchars           1.2          1.9               1.8
Gogarbank         1.8          1.8              1.9

So Leuchars was 0.6 C colder in December 2009 than Edinburgh Gogarbank meaning winter 2009/10 was 0.2 C warmer at Gogarbank than Leuchars with a mean of 1.8 C.  This changes ranking from 10th equal coldest to 12th equal coldest since 1765.

So winter 2009/10 in Scotland was around 10th to 12th coldest in the last 245 years, so exceptionally cold. The low temperatures of this  winter will certainly have an impact on spring phenology but this effect could be counteracted if spring temperatures are above average. On the date this post was written (21 March 2010), March temperatures are running circa 1 C below average, so late spring phenology is still expected. The winters of both 1979 and 1982 were similarly cold so spring phenology comparable to those two years can be expected.

Some effects are already in evident in Glasgow with daffoldils still not out (they won’t be long!) and crocuses in full bloom. Frogs spawn which normally appears in the first week of March has only appeared a week ago.

So how might butterflies be affected?  As of 21 March, the sightings page for 2010  shows first records for three species: Red Admiral 9 February; Peacock 7 March; and Small Tortoiseshell 12 March. These three species overwinter as adults so can be active as soon as a warm spring day appears. However, the Red Admiral is a migrant species which is considered unable to overwinter in the UK as the winters are too cold for it.  So this is a surprising record given the severity of the winter but it is thought that some individuals have successfully overwintered in southern England in recent milder winters.

The extent to which the spring phenology of our butterflies and moths will be affected this year depends on how they overwinter. The different overwintering strategies are detailed in this blog article. As shown in the paragraph above, species which overwinter as adults are least affected provided that they can withstand low temperatures. Those that overwinter in the pupa/chrysalis stage are also able to respond quite quickly to spring warmth but are likely to be delayed somewhat this year. The Orange Tip and the other Whites overwinter as pupae and are on the wing early in the spring but might be delayed a week or two this year.

For those species which overwinter in the egg or larval stage, the cold winter is likely to have a larger effect as the caterpillars must feed on plant leaves to continue their development. And the much lower soil temperatures which will be present this spring will certainly delay spring growth and bud-burst by several weeks. So the caterpillars which have survived the winter will have to remain hungry until the leaves on which they feed appear and for those which overwinter as an egg, egg hatch will be timed to co-incide with bud-burst, and this will simply be delayed. But the effect of this will be that butterflies and moths which overwinter as larvae or eggs will have their development delayed so their appearance as adults later in the year will be delayed.

So some of the  Fitillaries, Browns, Skippers and Blues could be delayed by up to several weeks this year. So we will all have to be more patient than usual! But it will be interesting to see how long each species is delayed and whether or not there are other effects. We might well see a dramatic drop in Peacock numbers in highland Scotland where temperatures have been very low as adults are not considered frost-tolerant but other species may increase in number if winter predation has been reduced by the cold winter.  By doing butterfly and moth recording this year, valuable data will be obtained which will greatly increase our undertanding on what effect cold winters have on a particular species. So please get and out and about recording!

Written by Andrew Masterman

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