Nature Notes

LARRY PENNY

The autumnal equinox is behind us. "The days grow short . . . one hasn't got time for the waiting game." Kurt Weill's message applies not just to humans, but to all life, and the ephemeral butterflies are no exception.

The monarch that travels so many miles is not only an enlightened monarch but a survivor, a classic survivor in the Darwinian sense.

One in particular hasn't got a lick of time to wait, and that is the monarch. The vast majority of butterflies escape the cold season by overwintering as cocoons, young of the year ensconced in furry pupae, but not the monarch. It chooses to go south.

Three-quarters of the population in the Northern Hemisphere spend summer above the early October frost line. Much more than three-quarters spend the winter in the canopies of southern trees, the bulk of which are on mountaintops in the Mexican Rockies.

Millions Of Wingbeats

It's a long way to a jamboree in central Mexico from jump-off points in Canada and Maine, and them that waits are them that don't make it. There's no time for lingering or loitering, only for nectaring and overnighting. All sightseeing is done on the wing.

It's a long way to the shelter of those tropical pines - for some monarchs, 2,000 miles!

Without a tailwind, top speed for a monarch is about 15 miles an hour, average speed during migration about 10 miles an hour. At about 180 wingbeats a minute (the foot speed of a very fast-stepping marching band on the college gridiron), the migrating monarch moves its wings up and down 720 times every mile, 7,200 times every 10 miles.

The ones traveling the farthest to reach the wintering grounds beat their wings 1.44 million times. No wonder their wings are so ragged when they finally achieve their destination.

True Flight

In nature, active flight evolved independently in three different animal groups: the insects, the birds (from flying reptilian ancestors), and the mammals. The flying fish has been well studied in this regard; after careful analysis it has been termed a "glider," in a class with the flying lizards and flying squirrels, not a "flier."

There are no flying amoebae, jellyfish, starfish, crustaceans, amphibians, or mollusks; there are no flying clams. Think of it - true flight in nature is an exceptional thing.

Exceptional

No aeronautical engineer has yet successfully designed and flown a plane based solely on butterfly flight mechanics. The wings of the mythological Icarus were half-bird, half-butterfly in design and action.

Bats' wings combine attributes of both. Though their flight surfaces are as tissue-thin as butterflies', their wingbeat motions are more like birds', even though bats flutter like butterflies. Some bats also migrate for long distances; they're pretty good fliers as well.

The monarch butterfly is an exceptional thing. It could have taken the easy way out, following the lead of the other butterflies. It could have evolved overwintering quarters for its caterpillars the way they did, expired gracefully before the snow and ice arrived the way they did, and put all its eggs into one basket, the spring emergence of the next generation, the way they did.

But it didn't. It took a different route. It developed long-distance migration.

Is It Instinct?

The migratory strategy in cold-blooded organisms (and many warm-blooded organisms as well) is only good if it gets you from a seasonally cold place to a warm place. If it does nothing more than move you from one potentially frigid spot to another potentially frigid spot, it will never work. Forget it.

In creatures that have culture, as in most birds and bats, the adults, or parents, rear and train the young, who continue to learn during and after migration from parents or other adults. The culture, however thin, is transseminated across migration. From a developmental point of view as well as a basic drive survival point of view, the migration can avail its practitioner great advantage.

In the case of the monarch there is no parental care, no adult care, no culture, as far as we know. Everything is pretty much instinctual - or is it?

Good For The Soul?

Hive bees in nature learn and transmit their knowledge, say by way of the figure-eight dance. Why can't monarchs in nature learn too?

Perhaps they do. Maybe milling around in massive clusters in the tops of those montane pines at the end of an arduous migration is good for the monarch soul.

Maybe it energizes, revitalizes their reproductive drives, prepares them for the return trip north in the spring.

There just could be a monarch culture.

Severe Test

If there is no cultural advantage, there are some decidedly primitive ones.

The overwintering cocoons in northern climes are not fail-safe. They can be exposed to the elements in various ways and be damaged or destroyed. They can be predated. They can open prematurely during the winter or early spring.

The adults that produce the eggs, the young, the young in those cocoons, are tested before they reproduce, but to what degree? Are they tested to the degree that the monarch is tested?

No. Never!

The monarch that travels so many miles is not only an enlightened monarch but a survivor, a classic survivor in the Darwinian sense. A 2,000-mile migration is not a run for fun. A few of the migrators might be just crazy nuts, but millions of them, not.

There is something vigorous, almost magical, Jordanesque, about the surviving monarch and its genes that should be passed on to future generations to give them an advantage in a competitive world. In the insect kingdom it is very competitive.

Before the monarch could successfully develop the long-range migratory strategy, it would have had to make itself over to catalyze the development. It would have had to become a very strong flier in relation to most other butterflies. It has done that, of course.

Wing Supports

Lepidopterans are covered with thousands of smooth, tiny, overlapping regenerative scales, a preadaptation toward flight. The scales are the "tiles" of the modern rocket ship. They are frictionless and replaceable. They reduce turbulence, promote stability, lend strength.

The wing supports - those very thin, darkish, elongate "sticks" we see against the sky stretching the wing membranes taut as the monarch flies overhead - are among the strongest materials known to science. If we could reproduce them in larger dimensions and different sizes, they'd have hundreds of structural applications.

But long-distance flying apparatus is not, in itself, enough to insure the overall success of the migrational survival strategy in monarchs. Two other survival mechanisms had to be working perfectly in order for the monarch to become the sublimest of migrants.

Survival Mechanisms

Flapping the wings 180 times every minute for eight to 10 hours a day burns up a lot of calories, a lot of BTUs. In order for a butterfly to fly it has to be very, very light - for its size, much lighter than a bird.

The monarch is as big as a hummingbird, yet 50 times lighter. It has a spindly abdomen and no extra space to store fat or calories. It has to feed as it migrates.

It is not a moth; it cannot find its nectar in the dark by its scent. It has to migrate during the day and find its nectar sources with its eyes.

Given those limitations, it is a very adept diurnal nectarer and can feed on a wide variety of flowers.

Nectar Omnipresent

Fortunately, fall-blooming flowers, to wit asters and goldenrods, are found throughout most of North America, and barring a widespread drought, there is generally no shortage of nectaring spots between the North and the South.

The second mechanism is not a general lepidopteran feature. It is peculiar to the monarch and a few others. It was developed late in butterfly evolution, perhaps by chance.

Migration can be a gauntlet, especially daytime migration. Predators follow; predators are stationed along the way. There are always lot of predators around to man the gauntlet. Butterflies are relatively slow fliers and are relatively easily predated, especially when nectaring, compared to birds and most other large flying insects.

Enter Milkweed

There would be a very small probability that a butterfly starting out in Canada, and flying only during the day, could make it all the way to Mexico without being predated.

Enter the milkweed. Monarchs are milkweed butterflies; they lay their eggs on milkweeds and dogbanes, members of the Asclepidaceae, which produce milky saps containing, depending upon the species, various foul-tasting poisons. The poisons are toxic to most insects and other animals, but not to the larvae of milkweed butterflies.

The poisons are accumulated and passed on from larva to adult. Throughout its life, the adult monarch is poisonous - more so when fresh out of the pupa, less so at the end of its journey.

Agent Orange

It only takes one bite by a would-be predator to learn to avoid monarchs in the future. The orangy colors and their patterning are learned in that one bite.

In fact, that particular orangy pattern has universal significance where predators are concerned. Many orange or partially orange organisms are toxic; some, like the Taricha newts of California, very toxic.

In general, orange organisms are to be avoided when other, non-orange ones, are available.

This is a kind of generalized mimicry. The viceroy butterfly has evolved to look and fly very much like the monarch. It mimics it, but is not poisonous. In fact, it is rather tasty to many predators.

Where monarchs and viceroys live together, viceroys are protected by the monarchs' warning coloration.

Tolerance For Poison

Without milkweeds and dogbanes, where would the monarch be? Most likely it would be a much more sedentary butterfly, with commonplace habits like the others', than it is now.

Did the monarch's penchant for milkweeds and dogbanes happen early on, or was the monarch sedentary for most of its existence, and only lately become migratory? In any event, the monarch's tolerance for milkweed poisons had to be developed before the larvae could feed on milkweeds.

Until that tolerance evolved, and then the ability to store up the poisons and pass them on during the molts to the adult, the adult monarch couldn't have gone very far. Now, the monarch's as free as a bird.