Blowing hot and cold over new theory

I have been intrigued by a relatively new theory involving weather cycles, that finds a link between warm and cool periods throughout the world related to the circulation of warm and cold water in the Pacific Ocean. It involves changes between warm and cool which last roughly 25 years, although the number of years in each cycle is quite variable. The link has been worked back several hundred years and seems to fit.

It suggests we entered a cool period around 1995, but it is unclear as to how far the world warming tendency might negate its effect. If you think back in 25-year blocks, the years 1970 to 1995 were definitely warm. But 1945 to 1970 had two serious winters in 1947 and 1963, and some cool summers. The period before that was relatively warm. A "cool period" doesn't mean to say all years will be cool, but some may be exceptionally so. Last year the severity of the winter made us realise that we haven't yet lost cold weather for good. If the theory is right, we might expect more winter surprises before we switch to warm again around 2020. It could also affect the success of our butterflies

and moths.

Just as I was thinking that all our butterflies seem to have melted away, the rain cleared, the wind dropped and suddenly a neighbour's buddleias were full of them – 16 Small Tortoiseshells and nine Red Admirals, and well into September. One of those buddleias was given its annual cut-back in late June. But it is proving its worth, with a mass of September flowers. If you want to attract butterflies to your garden at this time of the year, don't forget the value of rotting fruit. Some of our most colourful species enjoy fruit eating as much as taking nectar. We put out a tray full of over-ripe plums and within minutes we had a visiting red admiral vying with the flies and wasps. Yes, that can be a bit of a problem, but the wasps are so busy feeding they are not usually interested in stinging anyone. I wonder if you have noticed any horse chestnut trees with leaves turning brown during high summer, and now in September looking very autumnal.

If you have, the chances are the tree has been taken over by a moth. It is called the horse chestnut leaf-miner because the caterpillar crawls around the leaves between the two outer skin layers while eating the plant material in between. It tends to make patterns of brown marks following the arrangement of ribs on the leaf as can be seen in my picture. Looked at closely you can see the rounded edges of the mines formed as the caterpillar munches its

way around.

Surprisingly, this tiny moth was only discovered new to science in 1985 in Macedonia. Since then, it has raced across Europe, reaching southern England around 2000/02 and Yorkshire in 2007. By 2008 it had become relatively common in the southern half of the county and even reached as far north as Scotch Corner. This year I have noticed that in East Yorkshire it has become much more widespread. As far as anyone has observed so far, the moth doesn't kill the tree, but it may weaken it to a point where it could be affected by diseases. The conkers which result from an affected tree tend to be much smaller than average, not much good for a game. Apparently, the moth only infests the white flowering species, not the red one.

Keep an eye open for the raggedy winged comma, a woodland butterfly which tends to come into gardens in the autumn in search

nectar or fruit before going into hibernation. It has a white comma mark on the dark underside wings.

Howard M Frost is Butterfly Conservation's voluntary organiser of butterfly recording in Yorkshire and can be contacted via their website, www.yorkshirebutterflies.org.uk where you can also find regular updates as to which butterflies and moths are being seen across the county.