One of the advantages of using a trap every day, no matter how small it may be, is that over the years trends in moth abundance and diversity can be studied. I run a heath trap in my small back garden, and have done so for the last four years. Inevitably every year I have added new species to my ‘list’, but in the main the moths that I trap, even after a relatively short period such as this, are the same.
So, over the years, what species have been the winners and which the losers? The top ten has a familiar look about it with the Feathered Ranunculus the number one for three years out of five, not a surprise for this abundant coastal species. The abundance of this species has varied from a high last year of over one thousand one hundred to less than three hundred in 1996, this year saw just under five hundred. Other common and familiar members of the top ten have been the Large Yellow Underwing, Flounced Rustic, Garden Carpet, Lesser Yellow Underwing, Heart and Dart and Mottled Rustic.
Surprisingly only two micros have made it into the top ten so far – Crambus pascuella (96 and 97) and Agriphila straminella (96). Some moths have made brief appearances for just one year near the top. For instance the Silver Y was the fifth most abundant species in 96, a very good year for this migrant, with over two hundred, where as it normally only manages to produce around twenty individuals. Agriphila geniculea had a very good year in 96, with over one hundred and sixty, but was back down to sixty nine this year. Mottled Beauty has gone from fifteen in 95 through to thirteen in 96, three in 97 and none in 98. Least Carpet has shown the opposite trend with none in 95 then thirteen in 96, sixteen in 97 and finally thirty three in 98. This is clearly a moth that is extending its range, and becoming more common throughout the county.
Another moth that is notably establishing itself in Felixstowe is the micro Tachystola acroxantha, which first made its appearance in 97 with thirty one moths and showed up again this year with twelve. As yet I have not heard of any other records of this moth anywhere on the east coast so would be very interested to hear of other sightings, of this distinctive micro, elsewhere. Another micro that has shown a recent increase in abundance is the Pyralid Eurrhypara hortulata, this has grown from eight in 95, thirty two in 96, fifty one in 97 to sixty one in 98.
By looking at the figures it is possible to comment on nearly every moth that has found itself being counted in my back garden but I think that I have given a flavour of the types of observations that can be made if you record abundance. How much valid scientific conclusions can be drawn from this data is another question but these fluctuations must tell us something. Are they signs of changes in abundance that will be long term and significant or just random, chance observations? Is the weather an important factor, or possibly parasite cycles, food plant changes or some other natural phenomenon may be the cause of these varying observations? Only with continued trapping, in one place, can you find out – and that is why it is so interesting and important to trap as regularly as you can, and if time allows make a note of abundance.