Summer World_ A Season of Bounty - Bernd Heinrich [35]
Mutants of “motor” behavior (such as stepping, flight, climbing, walking, and reaching over gaps), learning, and memory are known, proving that behavior is indeed tied to genes. But how we get from protein gene products to programs of behavior consisting of hundreds of precise choices and actions—as opposed to behavioral tendencies—remains one of biology’s great mysteries. And here I met it head-on, right in front of my nose on our front porch.
7
The Blues
IT’S 12 MAY AND I’M AT CAMP IN MAINE. MR. WITHAM, who lives alone in a shack at the bottom of the hill, tells me that the ice was still on nearby Hills Pond last Friday. But today I heard the loons from that direction, so there is probably finally some open water. There is still snow along the roadsides, although the recent warm days have greened the aspens on some of the hillsides. Leaf-eating caterpillars are already on the trees, because swarms of warblers, vireos, and red-breasted grosbeaks arrived, almost to the day, as soon as the trees unfurled their leaves. It is warm and sunny enough today for the red Formicidae ants that live in and around my cabin to be active as well. They were running in a column up and down the trunk of the birch tree next to the cabin. A couple of the ants in the column were dragging a small caterpillar. I took it from them, and identified it as a species of “prominent” (notodontid) larva that I had in previous years found feeding on birch leaves. I then returned it to the base of the tree, and within seconds four or five ants almost pounced on it. But my most memorable sighting today was a tiny butterfly, Lycaenopsis argiolus, the spring azure. This butterfly is not uncommon when the poplars leaf out, and I may see more than one on any walk along the path up to my camp. The spring azure’s common name is apt, because this is the first butterfly to emerge from pupae that hibernated all winter (some, like the mourning cloak butterfly, overwinter as adults). It is hard not to be entranced by this butterfly. The surfaces of its sky blue upper wing glint like mirrors of the sky as it flutters over last year’s pastel-colored dead vegetation seeking the first spring flowers, often while there are still patches of snow on the ground. When the azure flies, there has been warm weather before it, and summer is not far behind.
Fig. 17. The spring azure and one of its pupae. The caterpillar is sluglike in form and is tended by ants.
The spring azures’ green sluglike caterpillars feed on buds and flowers of violets, and they are usually “tended” by ants. Ants kill most other caterpillars with little hesitation, yet they do not eat these caterpillars. Instead, they associate with them and repel predators as well as insect parasitoids, effectively acting as the caterpillars’ bodyguards. The secret of the caterpillars’ allure to the ants is that the caterpillars exude droplets of a sweet, protein-rich nutrient broth from glands on their backs when palpated by the ants’ antennae, and the ants lap this broth up.
MOST MEMBERS OF THE AZURES’ LARGE AND VERY INTERESTING family of butterflies, loosely called “blues” (although not all of them are blue), have small sluglike caterpillars. Few people except experts and aficionados (most famously including the novelist Vladimir Nabokov), who have studied them sufficiently to be able to distinguish them and name new species, know where to find them. But ants and these caterpillars find each other.
Many blues caterpillars are renowned for their close association with ants, and unlike the vast majority of caterpillars, some of these feed ants as the azure does, others move into the ant nests and are there fed by ants, and still others move in with the sheltering ants and are carnivores of their young. One thing has led to another in a likely evolutionary progression.
Once