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The Golden Egg Bug

03/26/02 12:00AM By Ruth Page

If a recent issue of Natural History magazine hadn't included photographs, I'd have had trouble believing in the ┐golden egg bug. Evolution, with quadrillions of scraps to work with, and endless time, turns out some life-forms that Rube Goldberg couldn't have dreamed up on his best day.

This bug seems to have been assembled by a demented scientist from scraps of furry leaves from common mullein weeds, plus a bunch of spines from a cactus. Two round yellow eyes sticking out from amid the spines indicate it's an animal with a head, so the long, skinny, jointed appendages must be its legs.

Entomologists describing golden egg bugs say they live in various Mediterranean countries, where they blend in nicely with dried parts of their host plants, members of the carnation family known as Algerian tea. We'd expect the bug to lay its eggs on that plant, as most other insects would. Not this bug. It lays its eggs on another adult golden egg bug. The stranger carries the eggs about on its body until the young nymphs hatch.

How does this help the female who laid the eggs to protect them? Somehow it must have evolutionary promise, helping to assure the eggs will thrive, hatch, and carry on the parents' genes.

There are male giant water bugs that carry eggs on their backs, and keep them aerated until they hatch, but those are eggs the male itself fertilized, so he has good reason to protect them. Eggs of the golden egg bug are glued to just about any body part of any total stranger, even its head or antennae. About a third of the eggs are stuck on female bugs, two-thirds on males.

Freshly laid eggs are white, but over time they turn a shiny gold. In about two weeks, out come tiny nymphs that depart, leaving their glued shells still stuck to the carrier. Occasionally there's a black egg. Research showed that these result from a minute parasitic wasp injecting her egg into a golden egg. When the wasp larva hatches, it eats the golden egg bug embryo.

The reason a male is more likely than a female to carry the golden eggs is that the male doesn't try to resist the glue process; he lets the female deposit her eggs, hoping that afterward she'll mate with him. Usually she's not in the mood, so he ends up protecting somebody else's offspring, with no reward.

When two golden egg bugs mate, they stick together, quite literally, for many hours; the female is larger, and hauls the male around behind her. Often, another female seeking a place to lay her eggs follows along in this peculiar parade until she's laid all her eggs on the pair ahead of her.

Entomologists discovered that ants which infest the Algerian tea plants love golden eggs, so there's good reason for the bugs not to lay eggs on host plants. Scientists conclude that the golden egg bug's behavior is not a permanent adaptation likely to continue as evolution moves on, but a temporary solution to the unexpected behavior of a particular species of ant.

This is Ruth Page, talking with you about one more of Nature's complex creations that can take mere humans years to figure out.

--Ruth Page is a writer and former editor of a weekly newspaper and a national gardening magazine.
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