Larval Doings

After moaning in various forms about the hard time that winter represents for most butterfliers, I’ve now encountered another period of lean pickings, the March – April gap, when the first hibernators appear in early March, injecting the first rays of spring-like hope into the year, before promptly it is promptly removed as the next cold front rolls in from the West. This time of year is arguably more fraught than winter, winter at least brings with it the comforting certainty that there are no butterflies to see, no precious moments of summer to snatch, but in the March – April gap, you can’t help but feel you should be doing more to seek out those first Orange Tips (this is of course foolish, the first Orange Tips always find you), and so it is that a new season of frustration is born.

To combat this, like winter, I have developed a daring strategy to combat this, turning to those shadowy brethren, the immature stages, this year, those orange sports-car butterflies – the Fritillaries.

Somerset is not as blessed with Fritillaries as perhaps it should be, High Brown was last seen at Hurlstone Point in about 2000, victim of extremely challenging terrain for management, and a lack of resources, and Pearl – Bordered Fritillary on Exmoor, up at Mounsey in 1992, whilst Marsh Frit is on the ropes, maintaining a transient presence up on Exmoor, and it would seem, hiding out elsewhere, with the exciting report of a larval web in East Somerset this spring, it remains to be seen if they will re-appear at Ash Priors this spring (fingers and toes firmly crossed).

A 4th instar Heath Fritillary Larva at Haddon Hill - 21/03

Despite this, it’s not all doom and gloom, indeed, one of our trademark species is a Fritillary – the Heath Fritillary. This shouldn’t really be a trademark, a rarity, since it was once a common enough species to earn its own nickname – ‘The Woodman’s Friend’, thanks to its dependence on managed woodland, where it breeds in areas of coppice, typically peaking 2-4 years after coppicing and then tailing off and having to move on to new areas. In coppiced woodland Heath Frits breed on Cow Wheat, laying eggs in small batches (averaging about 40) on and around the foodplant, typically growing in sunnier areas, often over bare ground. The key here – open coppice, sunny spots, reflective bare ground is heat – this butterfly is one of some that like it hot, and can’t survive without it, and so the rapid decline in coppicing sounded the death knell for most of its populations at the turn of the 20^th century, leaving it isolated in Kent (the East Blean Woods complex), and on the Devon-Cornwall Border. This meant then, that its re-discovery on Exmoor on 1984 was one of the great butterflying events of the last century, up there with Fort William’s Chequered Skippers, when strong colonies were found completely defying convention and flying between 200-400m (no other British colonies are above 100m) on moorland edges – they make ‘em hard in Somerset. This was at a time when the loss of the Large Blue had galvanised conservationists, and intensive study by Martin Warren, and some timely management changes ensured its future, though not before a rocky period on Exmoor in the 90s. Now it flies in quite a few areas on Exmoor, and most of its old 70s haunts, as well as several Essex re-introduction sites. Interestingly, its foodplants at the Devon and Cornwall sites (where it flies in old hay meadows and railway cuttings) are Germander Speedwell and Ribwort Plantain – this catholic foodplant choice seems to preclude rarity, but it underlines the key point about Heath Frits – it is the quality of the foodplant, the heat, that is key.

Nowadays a future for this butterfly in our fair isle looks relatively assured (though recent UKBMS results indicate it has declined by 82% over the last decade), with BC’s Two Moors butterfly project just finished, and currently its All the Moor project helping it along on Exmoor (with lots of great management by the National Trust’s Holnicote estate), and I’m lucky enough to have a thriving colony up the road at Haddon Hill, and so it was that I paid them a visit on the 21^st of March. The larvae hatch from their egg batches after a couple of weeks, and feed companionably together in a small web before dispersing in their second instar, and in September, in their third instar, spinning up the edges of dead leaves near the ground and moulting into their fourth instar and going into diapause. They emerge, phoenix-like the following year, basking on dead leaves as their foodplant germinates around them, often in friendly little groups. These larvae were my target on my visit, and after about 20 minutes searching, I struck gold, 2 singletons, and a happy trio all in a small area of bilberry at the bottom of the slope where they fly (about 6 metres from the wood edge, so nice and sunny) where the Cow Wheat was just getting going. They were laid out on dead Birch leaves on the moss through which the plants were growing, on the edge of a trampled Pony track (providing a sheltered little ‘valley’ for them) – sheltered, sunny, like everything with the Heath Frits – it screams heat. These weren’t up to much, and didn’t move in the hour I watched them – living the good life evidently.

4th Instar Heath Frit larvae at Haddon Hill (21/03), singleton in the left circle, and trio in the right
note the warm dead leaves, relatively open bilberry growing through moss (where Cow Wheat is germinating)
and the small path (foreground) creating a sheltered little valley.



A single 4th Instar Heath Fritillary larva on the circled leaf - a warm, open mossy hollow, on 11/04 about 20 larvae were here.

Impressed by these spiny little creatures, I decided to return to see them in their magnificent final form (6^th instar) later on, I made good on this on the 11^th April and was glad I did, for a larval horde awaited, with 36 counted lounging about amongst the Cow Wheat in 45 minutes of not especially intensive searching/photography. When a caterpillar is so common you have to watch your feet, it is a butterfly unashamedly thriving – and it’s good to see. Once again they were all intent on getting warm, basking either on the moss through which the foodplant was germinating, or once more, the dead leaves. I think the key to my lucky strike probably had a lot to do with the area I searched, one of the most open patches of the site, with the largest quantity of these warm moss mats, as opposed to denser areas of bilberry where the cow-wheat is closed out and the ground shaded and things are less suitable for the larvae – heat, heat, heat! I haven’t yet decided what instar these larvae are – they look very similar to the fourth instar larvae of the month before, but with more white spotting (is this just more obvious because of their larger size?) – I’d be interested if someone knows.

A Heath Fritillary larval horde, the two on the right are on a small Cow Wheat seedling (you can see some nibbling to the left of the middle one) - where there is one, there are often more!

Heath Fritillary larva at Haddon Hill 11/04 - not too sure what instar

Heath Fritillary larva basking at Haddon Hill 11/04

This area had about 30 of the larvae I found - note how much more open and mossy it is than the surrounding area, at the bottom of the slope - sheltered and warm, Cow Wheat was germinating in large quantities.



The same area from the other side.

Heath Frits were not the only larval target this spring. More to follow!