Saving the Large Blue Butterfly

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Large Blue Butterfly
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I'm always fascinated by tight and intricate relationships in nature. Sometimes the effects are unpleasant — malaria that goes from human to mosquito to human. But we expect that from microbes. The ones that fascinate me more are species that live a precarious balance, dependent on one our two key element in their environment. In the Sierra Nevada, Clark's Nutcracker's are deeply dependent on the whitebark pine which supplies most of the Clark's nutcracker calories. But the whitebark pine can't actually reproduce just by dropping seed on the ground. It needs to have someone bury its seed for it, and that someone is generally the Clark's nutcracker. Scientist believe that Clark's nutcrackers are responsible for planting ever single stand of existing whitebark pine in the Sierra Nevada. We think of the Chickaree as the forester of the Sequoia grove, but the Nutcracker is all the more the forester of our high-altitude forests of whitebark pine where few other trees grow.

All well and good, but I recently learned the extraordinary story of the Large Blue Butterfly (Maculina arion), which went extinct in England in the 1970s. See the numbers crash, conservationists fenced off LBB habitat from collectors and their nets, only to see that accelerate the decline because they had not yet understood the biology of the butterfly. As it turns out, the LBB lays its eggs on thyme or marjoram plants. There the catepillar gorges itself on herbs. When it's ready to go into its chrysalis, it drops to the ground secretes a sweet fluid that attracts a specific ant, the species Myrmica sabuleti, who carry it back to their nest where it proceeds to gorge itself on ant larvae and eggs until it's ready to attach itself to the roof and build a chrysalis around it. The LBB is so adept at matching the smell and sound of M. sabuleti, that the ants leave it alone even as it eats their young. It eventually emerges as the beautiful LBB. The ants will even escort the butterfly out of the nest and protect it from predators as it dries out and prepares to fly.

Now this life cycle is utterly dependent on that one species of ant. Other species might adopt the LBB, but scientist found the catepillar was five times more likely to survive if it were adopted by M. sabuleti compared to adoption by any other species. So for the LBB to thrive, there needs to be an overlap between areas where thyme grows and where M. sabuleti live.

It turns out that the disappearance of the LBB in England was not the result of overzealous collectors, but the result of declining populations of M. sabuleti. This in turn was the result of declining populations of rabbits, which was the result of the accidental introduction of the disease myxomatosis. When rabbit populations fell, the grasses grew taller. This shades the ground and has the effect of lowering the soil temperature. M. sabuleti likes a warm soil, and when the soil cooled from longer grasses, other species of ant outcompeted it. When conservationists fenced off LBB habitat to keep collectors at bay, they also prevented some grazing animals from accessing the land, which in turn accelerated the growth of grass and the cooling of the soil.

Conservationists first restored the thyme grasslands to good habitat for M. sabuleti, then introduced the ant, waited some years for populations to grow, then reintroduced the LBB, which now exists in over 30 separate colonies, some having as many as 4,000 individuals. It's a great conservationist success story, but also an incredible tale of how deep one must understand nature in order to be a proper steward and yet another demonstration of the famous John Muir quote: ""When we try to pick out anything by itself, we find it hitched to everything else in the Universe."

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