Dear Readers, on Thursday I attended an online talk about London butterflies, given by Simon Saville, who has been studying the lepidoptera of London since 1992 on behalf of the Field Studies Council. You can watch it (and the other talks that have been given during lockdown) here. However, I wanted to summarise the key findings here because they are really quite exciting. Back in the 1980’s, only 22 of the most generalist butterfly species were found in Central London, and apart from a few large areas, such as Hampstead Heath and Richmond Park, no areas within Greater London had seen more than 25 species. Then, there was a big recording effort back in 2019, which revealed more than 30 species, with several butterflies making an impressive comeback.
One of these was the pretty white-letter hairstreak (shown above). This was a butterfly whose life cycle was inextricably linked with the elm tree: it lays its eggs on the leaves, the caterpillars pupate in crevices in the bark, and the adult butterfly can most frequently be seen dancing above the leaves of the tree. When Dutch elm disease struck, the numbers of the white-letter hairstreak fell precipitously, However, just recently it has been staging a comeback: it seems that it is perfectly happy with the disease-resistant varieties of elm that we are planting, such as New Horizon, and so it is now being spotted regularly wherever there are elms (Tooting Common is mentioned as a particular hotspot). I shall have to check out the elms planted on Queen Victoria Street in the City when/if I ever get back to my office.
The second species making a comeback is the marbled white (Melanargia galathea) which, in spite of its appearance, is actually a member of the brown butterfly family (Satyrinae). Simon Saville described it as ‘a caterpillar with a short butterfly phase’ – it lives as a larva for over 11 months, from July right round to the following June, before pupating for about six weeks, emerging as an adult to mate and lay eggs and then dying after flying around until mid August. The larval stage is the most vulnerable, because who can resist a juicy caterpillar? Certainly not the birds in my back garden. But habitat reclamation seems to be working wonders for this creature – the caterpillar lives in unimproved grassland, feeding particularly on red fescue. It seems that all those unmown corners, the reduction in the use of biocides by local councils (who still use such chemicals on street weeds but are largely avoiding them in parks) and a greater awareness of the needs of wildlife by the general public are all having an impact. So, resist the urge to mow every bit of your lawn, and leave some not just for the marbled white caterpillars but for many other butterflies and moths as well.
And finally, the brown argus (Aricia agestis) is also making a comeback in London. This most unlikely species was formerly thought to be a specialist, with its caterpillars feeding only on rockrose (Helianthemum nummalarium) on chalk downland. But somehow this butterfly has switched its foodplant: the caterpillars have discovered a liking for the foliage of wild geranium species, in particular dove’s foot cranesbill (Geranium molle) which can be found pretty much everywhere in the south of England.
So, three success stories, to help to offset all the misery. It has never been more important to keep our eyes peeled, both in the garden (if we have one) and when we’re out and about on our exercise walks (if we’re able). There are discoveries to be made right under our noses.
And finally, I had to share the latest squirrel news with you. I had only just gotten over the fact that my resident squirrel babies were pretty much all grown up when I looked out of the window yesterday to find three new youngsters raiding the bird feeders, digging up goodness only knows what and generally wreaking havoc. What little rascals they are! My jasmine has become a jungle-gym, and they are showing a particular liking for the strawberry tops that my husband throws out, ostensibly for the birds.
Here are a couple of short films of their shenanigans. Enjoy!