Millions of Monarchs, Bunches of Beetles
How Bugs Find Strength in Numbers

Harvard University Press, 2000

Posted April 14, 2000 · Issue 76

Gilbert Waldbauer has devoted Millions of Monarchs to a survey of these bugs and the evolutionary advantages their collective behaviors serve. Although the author writes simply and elegantly, so as to be accessible to a wide audience, few entomologists will fail to find something new in this book.

The periodical cicadas, found only in the eastern United States, are one of Waldbauer's showpieces. Cicadas, whose grubs feed on tree roots, are found around the world. Big and slow-moving, they mostly depend upon hiding and good camouflage to escape birds and other predators. But the periodical cicadas have abandoned any hint of avoiding predation: fat and tasty, they perch en masse in the open on trees and sing one of the loudest songs on Earth at 80 decibels.

And predators, ranging from birds to snakes, raccoons, dogs, and even humans, do find them and gorge themselves. But plenty of Magicicada tredecula and Magicicada septendecula, the 13-year and 17-year species, survive - because there are just too many to eat. A 1956 brood of 17-year cicadas that emerged near Chicago achieved densities of 1,500,000 per acre in lowland forests. Over the several hundred square miles the brood covered, this added up to a billion cicadas - 533 tons of cicadas - per square mile. Millions may perish, but even after heavy losses, hundreds of millions mate and lay eggs.

Waldbauer demonstrates that this "survival of the mostest" strategy works. In cases where scientists have transplanted only a few thousand periodical nymphs to new locations, every last individual is gobbled up as it emerges. The tactic of overwhelming predators with numbers succeeds as a survival strategy, and periodical cicadas have not had to develop fast flight or cryptic coloration. By choosing such long periods between appearances - 13 and 17 years, with few overlaps in any one area - the cicadas have prevented any predator or parasite from evolving a dormancy period long enough to emerge when they do. The result is one of the slowest-growing insect species known.

But not every species that chooses to overwhelm predators waits years to emerge by the millions over a period of weeks. Mayflies, the order Ephemeroptera, usually emerge by the millions in just a few hours. The aquatic nymphs of mayflies live in lakes and streams, and the adults emerge at the surface of the water. The closely synchronized emergence results not just in birds too gorged to fly; some lakeside towns have had to use snowplows to clear this summertime abundance from streets.

Not all the behaviors that Waldbauer explains are about avoiding predation. It is not clear whether the silk pavilions spun by tent caterpillars thwart predators or parasites, but they do provide air conditioning. The microclimate inside the tent is reliably warmer and more humid than outside air.

Other insects that prey upon trees need help overcoming their defenses. Douglas firs attacked by bark beetles burrowing into their flesh counterattack with streams of resinous sap that immobilize and suffocate the bugs. But some bark beetles release aggregation pheromones, chemical signals that are detected by members of the same species miles away, calling them to join the feast to the point that the tree's resin supplies are exhausted.

Waldbauer devotes chapters to two of the most famous examples of group behavior in nonsocial insects, the migratory locust and the monarch butterfly. The desert locust has been a well-known plague since Egyptian times, perhaps even longer. Waldbauer relates the astonishment entomologists felt when Boris Uvarov realized in 1921 that the incredibly destructive migratory locust was one and the same species as a comparatively innocuous grasshopper found only in modest numbers. Perhaps Waldbauer's greatest strength - having read so much of the scholarly literature, and being able to synthesize it - is on display here. He explains how a clever British scientist designed a little wire brush, powered by an electric fan, which stroked solitaria locusts - and caused them to transform themselves into gregarias.

The monarchs and their unique strategy of overwintering in a few isolated Mexican and Californian forests are quite well-known, thanks to the efforts of lepidopterist Orley Taylor. Waldbauer explains their reasons for gathering by the millions in winter - and also uses the monarch as a springboard to explain various forms of mimicry. He also takes the opportunity, one of several used in Millions of Monarchs, to describe the imperiled state of the monarchs, caused by logging in the woods they need for survival.

The only weakness I can find in this very readable book is Waldbauer's reluctance to let any good story escape. The tales from medieval and more recent times of using prayers or holy water against insect plagues, or bringing grasshoppers up before ecclesiastical courts, are entertaining, but they have been told before.

And although he does a good job with Asia's synchronized-flashing fireflies, he does not have enough to say about New Zealand glowworm to make that snippet worth including. Otherwise, this is a fine survey of a group of organisms never before considered as a unit. The book is an excellent example of years of specialized research translated into an exposition of evolutionary biology at work.

Jonathan Beard has been a journalist since 1981, when he left his job as a librarian at Columbia University.

Sometimes political scientists or economists break human interaction down into zero-sum and non-zero-sum components. Occasionally, evolutionary biologists do the same in looking at the way various living systems work. My contention is that, if we want to see what drives the direction of both human history and organic evolution, we should apply this perspective more systematically. Interaction among individual genes, or cells, or animals, among interest groups, or nations, or corporations, can be viewed through the lenses of game theory. What follows is a survey of human history, and of organic history, with these lenses in place.

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Endlinks

An interview with Leticia Aviles - a University of Arizona researcher who specializes in social spiders.

Monarch Watch - here you can follow the migration of monarch butterflies; the site has plenty of information about monarchs and the fight to save their overwintering grounds.

Periodical Cicadas ("The 13-Year Locust") in Alabama - a comprehensive site where you can see, read about, and even hear periodical cicadas and other species.

Illinois Agricultural Pest Management Handbook - has a report on the corn rootworm, pesticides, and crop rotation from the farmer's perspective.

Synchronized fireflies - the Center for Connected Learning and Computer-Based Modeling at Tufts University gives this site an unexpected angle: it represents an assignment to engineering students to design a firefly, using electronics, that will not only flash but synchronize its flash. Since the students have to understand what fireflies do, there is good biological background here.

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