Friday, 15 April 2016

Window watching, serendipity and a tiny moth

The playwright Katori Hall wrote that serendipity always rewards the prepared.


There I was, shortly before lunchtime on Thursday 14th April 2016, sitting at my desk in Southover House, pausing mid-letter to watch the Rooks zip from their rookery at the front of the office past my window towards Pelham House and back again with their beaks stuffed with food, when a much smaller movement caught my eye. There, on the inside of my opened window was a small dark moth. Of all the 200-odd windows in all the rooms at Southover House, it chose mine! I dashed to the Rangers' desks close by, grabbed a pot and, a few seconds later, the little moth was safely inside.

Dan and I spent a few minutes of our lunch break checking through the list of species belonging to the Gracilariidae family of moths until Dan suggested that our little moth was Phyllonorycter rajella. It was confirmed the next day by County Recorder Colin Pratt.

Phyllonorycter rajella - the Common Alder Midget, found on Alder trees and on the insides of office windows


Phyllonorycter rajella (or the Common Alder Midget) is new to me - I had never previously seen it, mainly because its food-plant, Alder (Alnus), doesn't grow on the chalk Downs where I do most of my entomology. There are plenty of Alders close to Southover House though, in the Southover Grange Gardens and the Railway Land Local Nature Reserve. It is a widespread species, fairly common where Alders grow, but apparently easily overlooked - like most micro-moths.

The adult is on the wing during two generations each year, during May and again in August. It is very small: about 5mm in length with a wingspan of about 8mm. They have a white face and, if you look carefully in the photograph above, you can see that it has white tips to its antennae. The larvae feed on the inside of an Alder leaf, forming a mine on the underside and causing a mottled appearance on the upperside. This is described well, with photographs, on the British Leafminers website.

On checking Colin Pratt's A Complete History of the Butterflies and Moths of Sussex, P. rajella was first recorded in Sussex sometime just before 1859 by the eminent entomologist H.T. Swainton. That was the last time it was recorded in Lewes. I wonder how Stainton would have felt if he had been told that a gap of 160-odd years would be broken by a chance finding on the inside of someone's office window? Would he have chuckled or would he have shaken his head and mumbled something Latin in a hushed tone?

Most Sussex records of P. rajella are of leaf-mines. There is one record of a larva and, before yesterday, the only adult record was made in 1984, meaning yesterday's record appears to be the first adult seen in Sussex in 32 years.

When one considers the many miles trodden in the dark by Lepidopterists, burdened with heavy equipment, the hours of work dedicated to searching for an elusive species, the disappointment felt trudging back home after a fruitless search, this particular record of a moth which flew into the human world for the first time in more than three decades feels something like cheating. Sometimes serendipitous records such as this are a reward for those barren times.

Of all the windows in all the rooms at Southover House, this little fella had to fly in through mine.
References:

Pratt, C.R.P. 2011. A Complete History of the Butterflies and Moths of Sussex. Volume One. Independently published.

Pratt, C.R.P. 2015. A Complete History of the Butterflies and Moths of Sussex. Volume Four. Independently published.

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