Lucky me the other day — I was fast enough to get a clear photo of a blue butterfly flitting about the back garden. During our first summer here, butterflies were a rarity, and I’ve often wondered why. Now I know that a certain vetch and ants have to be around too — at least for the Adonis Blue (Polyommatus bellargus). It is called Niña celeste in Spanish (a slight confusion in gender, as it is the male that is blue; the female is chocolate brown).
The only food of the Adonis blue and its larvae is the Horseshoe Vetch, Hippocrepis comosa. A low-growing native plant that belongs to the bean family, it has yellow flowers, shaped like sweet peas, but no bigger than the nail on my little finger, arranged in a circle like a miniature crown. I don’t take any credit for them — they just appeared, the first wildflowers in our second spring here (except for the trees, the soil was totally bare when we got here), and once I’d identified it as a leguminous plant, and thus a nitrogen fixer, I was delighted to let it be.
Other gardeners would call them weeds. A weed, as the dictionary defines it, is a plant that grows where it is not wanted. Well, I love the Horseshoe Vetch in its own right, as its flowers are so cheering. I also love that it protects the precious soil from being baked by the summer sun and being washed off by winter rains. Precious because only a thin layer of it lies atop the limestone bedrock on which I garden. As well as fixing nitrogen — its most impressive and valuable function, in my opinion — it also interacts with myriad microorganisms living in the soil — bacteria and fungi and microscopic animals — that in their individual ways contribute to soil health and the plants grown in it (and when an imbalance occurs, to their ill-health too). Now that I know these lovely blue butterflies depend exclusively on the Horseshoe Vetch for their existence, I value these plants even more.
But the Horseshoe Vetch on its own does not guarantee that Adonis Blue will populate a garden. One has to have ants. Ants? Aren’t they enemies of butterflies? Not in this instance. Adonis Blue caterpillars exude a kind of nectar that ants are crazy about — to the point where they smuggle them into their underground nests to “milk” them. There the larvae are protected from predators and overwinter as pupae, safe from the cold and lovingly tended by the ants. There are several ants’ nests in the back garden that I have not disturbed (even when they disfigure other plants, such as the tender new shoots of the perfumed Lady of the Night, the Dama (also Galan) de Noche, Cestrum nocturnum, on which they farm aphids. The Lady of the Night eventually recovers and blooms.)
I am glad I haven’t taken steps to eliminate the ants. (They’ve stayed away from the house, thank goodness.) And as well that I’ve let the Horseshoe Vetch and its other bean relatives — considered weeds by others — remain. Had I not, I would not now be enjoying these amazing blue butterflies.
What an astonishing symbiosis between two insects that are usually arch enemies. Not only the Adonis Blue, but the Common Blue (also seen in my garden because it also feeds on another kind of vetch and other related bean plants) and most of the family of Lycaenid butterflies have this remarkable co-existence with ants (a relationship called myrmecophily) especially in Australia. The Lycaenid butterflies all have striking colours — mostly in the blue range — blue-grey, bluish-purple — but also copper or bronze. Are these brilliant colours somehow related to their sweet substances derived from these leguminous plants? Another of nature’s fascinating mysteries….
Olives, pines, and rocks 