Challenge on Nature Photography - Part 2

 

Today’s photo for the Challenge on Nature Photography (see yesterday’s post for an explanation), is of another iconic butterfly species, the enigmatic Large Blue. I’ve always felt honoured that such a rare and sought-after species lives a short drive from my home, up on the Polden hills, and as such, every year I make the pilgrimage to Collard Hill (the flagship site for this species, it does fly elsewhere), to pay my respects to this mythic butterfly, and help the National Trust show visitors the ‘star of the show’.

Why’s the Large Blue so rare then? Like many Lycaenids (‘gossamer-winged butterflies’, in the UK: Hairstreaks, Coppers and Blues), for part of its life cycle, it forms an association with ants (it’s a myrmecophile!), though, sadly for the hard-working ants, this isn’t the traditional symbiosis  - where the lycaenid larva provides sugary secretions for the ants, in exchange for protection (though it’s thought to have evolved from it), in fact, it’s a bit of a one way street.

Female Large Blues, roaming the slopes on limestone grasslands in Somerset and Gloucestershire (and some other places) lay their eggs singly on developing thyme flowers. After a week or so, the egg hatches, and a rather unprepossessing hairy, pink larva emerges. For a couple of weeks, it feeds on the thyme flowers, growing in size, and passing through several skin changes, so far so normal.

The fun then begins when the larva throws itself off the thyme flowers onto the ground (normally during the late afternoon), where it hopes to be found by one particular species of red ant – Myrmica sabuleti. Upon discovery, ants will then tap the larva so that it produces a sweet substance from its ‘newcomer’s gland’ on the 8^th abdominal segment. Sadly, this is about all the ants get from the larva, which then tricks them into thinking it’s an errant ant grub, causing them to rush it back to the safety of the nest. Without so much as a thank you, the larva then proceeds to munch its way through the ant brood, dining on their soft tissues, all the while secreting chemicals similar to those of M. sabuleti so as to enhance the deceit. This continues until, having grown fat on its protein rich diet, it towers, Jabba the Hut-like over its hosts, and is ready to pupate. This it does in a cell near the surface of the ant’s nest, making clicks that mimic those of the Red Ant queen (to ensure constant attention), before emerging from the nest after 3 weeks, protected by an army of red ant attendants, and expanding its wings to take its first flight.

Interestingly, the Large Blue’s scientific name – Maculinea arion (Phengaris arion to some) commemorates this remarkable life cycle. Arion was a Greek musician who was kidnapped by sailors who wanted to steal the prizes that his instrumental talents had brought him at a competition in Sicily. Arion, requesting one final song before his promised death, and such was the sweetness of his voice that he attracted several Dolphins to the prow of the ship. He threw himself from the prow onto one of the Dolphins, which carried him to safety. The whole story provides a nice allegory for the Large Blue’s life cycle – Arion is the caterpillar, the Dolphins are the ants, his beautiful voice is the larva’s sugary secretions, the boat he throws himself from the Thyme flower, and the shore to which he is carried the ant’s nest – neat eh?

 

Anyway, the survival of Large Blues is clearly controlled by the presence of Myrmica sabuleti (the only species which it is successfully adopted by, others will kill the larva, since the chemicals it secretes do not mimic their own). Unfortunately, M. sabuleti has very specific habitat requirements – warm south-facing slopes with sward of 1-2cm, generally on some sort of species rich alkaline (chalk/limestone) grassland. This is a rare habitat, largely dependent on finely-tuned grazing practices, and so M. sabuleti and the Large Blue are only really found on land carefully managed with their needs in mind.

When these needs aren’t met, extinction soon follows, and sadly, exactly this happened in the mid 20^th Century, when, thanks to a changing farming practices and myxomatosis cutting through British rabbit populations in the 1950s, many once ideal Large Blue sites became choked with the kind of rank, grassy sward that is this species’ nemesis. Fortunately, a pioneering reintroduction project has seen this amazing butterfly return from the dead and fly on limestone grassland across the south west once more.

The reintroduction is a brilliant example of science-based conservation at its best, before its extinction, the amazing ecology of the Large Blue was finally untangled by scientists, paving the way for the most successful large scale insect reintroduction ever that it’s return has been. The research didn’t stop there though, and Jeremy Thomas (the man responsible for the earlier untangling) has demonstrated a fascinating twist in the Large Blue tale.

As well as Thyme, the Large Blue uses Marjoram as a foodplant, and when ants attack this plant’s roots, it secretes a chemical called carvacol as a defence. This chemical is pretty nasty stuff if you’re an ant, and is generally an effective repellent for the marjoram, one species, however, has learnt to detoxify it, you guessed it, Myrmica sabuleti. Thus, the presence of carvacol around the Marjoram alerts female Large Blues to the presence of Myrmica sabuleti, and potential ‘foster parents’ for their offspring. This causes them to lay their eggs on the plant, and the caterpillars to engage in their usual parasitic relationship with the nest below. It’s a neat little system that’s advantageous for the Marjoram (the exhorbitant demands of the Large Blue larvae generally kill off the ant’s nest) and the Large Blue (it has guaranteed childcare), and so provides one of the first examples of insect-plant symbiosis (a you scratch my back, I’ll scratch yours relationship) – fascinating stuff!

The Large Blue’s amazing life cycle, rarity, and beauty are a winning combination for butterfly watchers, and it’s not difficult to see why so many lepidopterists make the pilgrimage to Collard Hill (in Somerset) and Daneway Banks (in Gloucester) to see it. Its reintroduction provides a compelling example of the success of a more ambitious approach to conservation, it may just be an insect, but perhaps the kind of support and following that this charismatic insect has won will give re-wilders hope, I for one would like to start small – Large Copper in the Cambridgeshire fens please!

 

The Large Blue - fluttering over Somerset's grasslands once more!