The annual rise and fall of the Large Yellow Underwing

One of the most striking things in the annual garden moth-trap data is the rises and falls, and then the big surge, of the Large Yellow Underwing, Noctua pronuba. For much of the year, its numbers are surprisingly modest. Most trapping sessions produce somewhere between zero and ten moths, and early in the year it is rare to see any at all. But punctuating that low background are some conspicuous little explosions in mid-summer: for me this year around 25 to 30 moths on 16th June, again on 9th July, and again on 13th August. Then, towards the end of August, something rather different happens. On 20th August there were only one or two. By 27th August the catch was around ten. Then it doubled to about 20, doubled again to around 40, and by 7th September, a night that got down to 14C and was wet from some point before dawn, it was almost 90. The next night was dry, but dropped to a similar minimum temperature and the numbers dropped too, to 74. The 7th September may well have been the…