Middlesex, Hertfordshire and the Essex border area by Andrew Middleton

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In 2005 Andrew Middleton volunteered to act as recording co-ordinator for TQ38 and TQ39. Both 2km squares are in Middlesex with TQ38 covering the first 10km square north of the Thames and TQ39 reaching Enfield and the M25.

My first sighting of White-letter hairstreaks came in the mid-1990s whilst out with Jeremy Gaskell at Sewardstone Marsh in the Lea Valley, Essex. We could see two or three small, dark butterflies jinking around the crown of a small elm, but we had to consult the books back home before we were sure what they were.

Over the next few years I became aware that elm, in varying health, was a fairly common plant in my neighbourhood of Middlesex/Hertfordshire/Essex, and that most trees held the species, and often in abundance.

However, none of my butterfly books suggest that this has been the case. One book suggested that 'experts', being present and recording in an area at regular periods over many decades, would have recorded these honey-dew feeders had they been present, and that the absence of records indicated loss through smoke pollution from the late 1800s through to the clean air act. But the species had long been recorded on elms in Battersea Park, within spewing distance of the coal-fired power station in the center of the big smoke metropolis. The book also gave White-letter as unrecorded in the author's home 10km square, which proved too much of a temptation for me. A quick visit one day found White-letters in abundance flying around the first group of elms to be found.

Habitat
Almost all the elm I've found in my area holds a colony, right down to unpromising single trees beside busy main roads in industrial areas. The species appears to me to be quite mobile and well able to disperse, as I have seen it several times flying well away from elm and it seems perfectly able to colonise quite isolated lone elms. However, there are four healthy elms planted at two sites in Enfield which are probably non-native trees. They seem to drop their seed discs quite early and I have yet to record White-letter on them. Other than that, I don't think the species is very demanding ecologically in my area.

A small area of planted elm in Durants Park, Enfield. So far White-letter have not been found! (see habitat notes)

My area 2005-6

White-letter Hairstreak distribution in TQ38 & TQ39 for 2005 & 2006	Purple Hairstreak distribution (in comparison) in TQ38 & TQ39 for 2005 & 2006

This is how far I have got in recording White-letter in the 2 x 10km squares where I live in North London. Purple Hairstreak distribution is shown for comparison. Elm and White-letters are fairly common across the green belt towards the M25 in the north of the TQ39. Elm and White-letters are also to be found in the suburban areas, usually in the old parks or along roads and railways.

Habitat supporting a White-letter hairstreak colony in Edmonton, North London

In Tottenham and towards the dreaded North Circular Road, elm becomes much scarcer, however the few patches I have found do hold White-letter colonies. Unlike for Purple Hairstreak, where oak is more common, I think I am going to struggle to find White-letter in the more urban 2kms in my 10km squares, simply because I haven't yet found any elm.

However, colonies of White-letters are still being recorded across the highly urban 10km square of Haringey, Islington, Hackney and Tower Hamlets through to the Thames. Elm trees are few and far between in this area, yet the White-letter still seems able to find them.

Compare its status to the other butterfly species recorded in these 10km squares: http://www.acmiddleton.pwp.blueyonder.co.uk/TQ38&39.htm

Birds and predation
Initial evidence of White-letter larvae damage can be seen through binoculars but closer inspection of a rosette of seeds with recognisable damage of a hole in the middle may find small larvae resting between the seed discs. Further inspection a few weeks later when the seed ages will often find the larvae on the leaves. This type of work requires good close vision which is something that Liz ducks on! A favourable elm can be smothered in bonanza grade larvae in spring. Andrew has often watched greenfinch, great and blue tits returning time and again to glean White-letter larvae, first from between the seed discs, then later from the leaves. On the shaded lower branches of one elm, I once found c.100 green larvae in early May. Later, when the larvae were turning purple-brown and pupating, I could only find about 25. Three 3 small larvae were obviously parasited, with a small fly emerging later from one specimen. Next visit I was down to one pupa. Not very scientific, but for me a clear impression of the way that White-letter can be abundant, and often provides a great food source for breeding song-birds.

For more information on searching for eggs and larvae visit Martin Greenland's notes  

Elm seeds with larvae - in the left picture the hole in the seed is clearly visible, the right picture is of older seeds © photo: Andrew Middleton

Andrew Middleton
January 2007