Saturday, February 25, 2012

The Camberwell Beauty

Insects living in the Temperate Zone need to find some method of surviving winter. A few strong fliers among the butterflies (e.g. Monarchs, Painted Ladies) or dragonflies (e.g. Common Green Darners, Wandering Gliders) can migrate, but these are exceptions. Bernd Heinrich with his famous "rectal thermometers for bumble bees" has demonstrated that a number of insects are warm-blooded (they use muscle-flexing to keep their internal temperature well above the ambient temperature), but these insects run into the problem that there is no food available in winter. As a kind of exception to prove the rule, I have often seen Blue-bottle Flies out and active in midwinter in sub-freezing temperature (down to 28 degrees). But these are carrion feeders, and carrion is if anything even more available in winter.

But in general insects survive winter through some form of diapause, a period of dormancy, and different insects have different strategies. In the case of insects with full metamorphosis, like butterflies, some spend the winter as eggs, some hibernate as partially grown larvae, some as chrysalises, and some as adults.

The last class is by far the smallest, fewer than a dozen in Arkansas. They are the ones you sometimes see out briefly on a warm day in midwinter, and of course they are the first ones out in spring.

Yesterday we went to Hatchie Coon Island in southeastern Craighead County, in the St. Francis Sunken Lands, a large area that sank twenty or so feet below ground level during the New Madrid earthquakes. The forecast was for the warmest day so far this year, and it was. There were high winds from the south changing to the west, intermittent clouds, and a temperature that reached 78. We noticed numbers of small crane flies out with lots of courtship in progress. Here's a photo of a pair. Note the extraordinarily long hind legs on the male.

Twice we saw adult pygmy grasshoppers, which we were particularly interested in, since the very early species might be ones we haven't seen before. But they disappeared before we could get good photos of them. Otherwise not much was going on. About 1:00 we stopped for lunch and while we were eating a Mourning Cloak landed on the dirt road in front of us. When this handsome butterfly is fresh (which was last summer) the cloak is a rich sable with a row of blue gems, and then trimmed with ermine. It is the mourning cloak of royalty. The species is found all over this country and throughout Eurasia, where it very occasionally makes it across the channel to England. There it is known as the Camberwell Beauty and is considered a prime rarity.  Cheryl's brother in England is a keen naturalist, but he has never seen one. I love sending him pictures and saying  "more of our backyard trash."

Here is the screwy life history: The species emerges from the chrysalis in the summer and if you are lucky you can catch a glimpse of it then in its fresh perfection. It tanks up on nectar or on sap dripping from injuries in trees. Then it more or less disappears from sight, estivating in the heat of summer, spending the winter behind loose bark or in a hollow tree. It reappears in the first warm days of spring, by that time so scratched and faded and tattered you hardly recognize it. Here is a summer picture followed by a picture of one of the ones we saw yesterday.

It is in that sorry state, seemingly at the end of their rope, that the males court the females. Though the roads had been empty when we arrived, now when we drove slowly down the same roads it seemed like there was a Mourning Cloak every fifty or hundred feet. These were all males, sitting on their territories. When we came up close to them we could see their tongues were out, and they were drinking up different salts from the mud of the road. These would go into the semen they gave the female, to help nourish the developing eggs. The other thing they were doing on the road was making themselves easy to see from a distance, to attract whatever females were around. Stop and think: If we are, say, a million times larger than an insect, then the insect lives in a world that is a million times larger than ours, and therefore a million times chancier for a male to find a female. This area where we were is very flat, and the bare roads make the males very visible. They further improved their odds by all appearing at a particular time: the afternoon. Another place we will begin finding butterflies right now is on hilltops. Lots of butterflies (and other insects) narrow down the odds of finding a friendly single by heading for the top of a hill. The hilltop draws up butterflies from all around to a single central spot. In the next week or so we will check some hilltops. On this particular day down on the flats we saw almost all Mourning Cloaks, but we also saw a handful of Question Marks, another butterfly that overwinters as an adult.

The surprise was, we also saw a small sulphur butterfly. In appearance (though we only saw it in flight) it was like either an Orange Sulphur or a Clouded Sulphur. Both species are quite yellow in color early in the year, and very difficult to tell apart. The Orange Sulphur is the commoner species here, but this one, with its smallish size, and pale yellow color, made me think it might be a Clouded. But the problem is, both of these go into diapause as half-grown caterpillars. That means when it begins to warm up in spring they must find an appropriate plant already leafed out so they can feed on it and complete their development as a caterpillar, then make a chrysalis, develop into a butterfly, and only then come out as an adult.

So where in the world did this one come from?

The battered and faded naturalist, after enduring a long winter, can be seen out on the very first warm days.

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