• Choose a category
• All
• Classic-Fiction

By Root 290 0

can actually benefit everyone concerned. Predators often do not gulp down the entire egg mass or group of babies. Instead, they usually nibble off a few eggs here and there, or they pluck the most vulnerable larva from a cluster. In such cases, it pays to be part of a teeming horde, because one's chances of being the unlucky victim go down the more options the predator has; if a wasp or spider snatches one egg, and ten are present, you have a one in ten chance of being eaten. But if one hundred eggs are in the mass, your chances go down to one in a hundred, much better odds. At the same time, guarding a mass of a hundred eggs isn't much more work, if any, than guarding ten. In a North American treehopper that lives on goldenrod leaves, the hatching success of broods that were supplemented with dumped eggs was 25 percent higher than that of broods reared with only their own brothers and sisters.

Given this happy everyone-wins scenario, why isn't egg dumping even more common than it already is? Tallamy suggests that the opportunity to dump eggs may be constrained by the size of the nest (if eggs have to be placed in a particular spot, for example, a stem, at some point there is no room left), the physiological capability of the female to keep producing eggs, or the synchrony among females in their reproductive stage. It does no good if you have eggs to offload if all the other nearby females are already half-way through the process. Finally, the kind of care given, for example, guarding, has to be such that it can't be much costlier to administer it to a large brood than a small one, kind of a cheaper-by-the-dozen effect.

Brothers, Sisters, All?

SOMETIMES even the most acute sibling rivalry has to take a back seat to cooperation, if cooperation is the only way to survival. A bizarre example of this perhaps begrudging all-for-one and one-for-all strategy occurs in a flightless blister beetle found in the sand dunes of the southwestern United States. The adult beetles eat, and lay their eggs on, an attractive purple-flowered plant called a milk vetch. But the larvae can't survive on the plant and instead are parasites in the nests of a solitary bee that also occurs in the desert. So how do you get to a bee's nest miles away over scorching sand when you are a baby beetle about the size of a poppy seed?

The answer is one of those You Couldn't Make This Stuff Up stories at which insects excel. Immediately after they hatch, the larvae make their way up to the tip of a plant stem, where they cluster together in a clump of anywhere from 120 to over 2,000 individuals. Viewed collectively, the clump resembles a female of the host bee species. They then emit a chemical that mimics the sex pheromone of the bee, which attracts a male bee eager for romance. When the bee lands and attempts to mate, some of the tiny larvae leap onto his back and are transported away from their siblings. They then transfer to a female bee during copulation when the hapless male eventually manages to find the real thing, and finally are taken to their goal of her nest when she flies back, replete with sperm and her minute beetle passengers. Once inside the nest, the larvae hop off and feed on the pollen and nectar the bee has brought back for her own offspring. Finally, they emerge as adults, to start the whole improbable cycle again.

Where did this bizarre life cycle come from, and why do the beetles rather than other—perhaps many other—kinds of animals exhibit it? We don't know for certain of course, but the sheer number of insect species may have provided a larger canvas on which to paint different pictures. Many of them probably died out before they became established, but a few, like this one, remained.

Although this scenario brings up many interesting issues, from the standpoint of family relationships it is like one of those conundrums of which the philosophers are fond. A male bee can hold only so many larvae, a fraction of the aggregation. But all of the members of the group have to cooperate to constitute a convincing mimic of a female bee.