Sex on Six Legs_ Lessons on Life, Love, and Language From the Insect World - Marlene Zuk [77]
Not My Problem
RATHER than deal with quarreling offspring or hungry mouths, some insects whose young require care after the eggs are laid have abdicated at least some of that care entirely. We've long known that cuckoos, cowbirds, and a few other bird species are brood parasites, which means that females lay their eggs in the nest of another species, the host. Some ants do much the same thing by using a different species of ant to rear their young, either by capturing eggs of the foreigners and bringing them back to the nest or by killing a queen and replacing her with one of their own kind.
More recently, a more subtle but no less effective means of getting someone else to do the work of child rearing has been recognized in both birds and insects. Rather inelegantly but descriptively called egg dumping, it means exactly that: depositing eggs into the nest of another member of the same species. Often a female that practices egg dumping still cares for some of her own eggs, but the farmed-out offspring serve as a kind of bonus rainy day account, allowing her to literally not put all her eggs in the same potentially vulnerable basket. In other cases, skipping out on maternal care means that a mother can keep churning out batch after batch of eggs at a rate that a mother spending time and energy on demanding offspring could not equal.
Lace bugs, delicate insects with filigreed wings that live on a variety of garden plants, face a trade-off between protecting their young from predators and losing future reproductive opportunities by doing so. Doug Tallamy has studied maternal care in several kinds of lace bugs, and found that they will keep laying eggs in the egg masses of other females and abandon them to the care of the female that first started the egg mass. They keep doing so until they cannot find another suitable host, at which time they proceed to guard their own eggs and offspring, presumably along with those that other females have foisted onto them.
The burying beetles will also engage in a little stealth egg laying if their carcass has been taken over by another pair. The defeated female will stay near the dead animal and sneak into her former nursery to feed on the carcass herself and surreptitiously lay some eggs. Sometimes, if the carcass is large enough, she is even tolerated by the female in possession of the corpse, and both remain to rear their young in the same underground chamber.
As with infanticide, egg dumping used to be dismissed by biologists as an aberrant behavior that occurred because the female was too stupid to figure out how to breed properly; an early researcher who discovered egg dumping in ducks rather pejoratively called it "careless laying," and "degenerative." Presumably the idea that a mother would callously abandon her own offspring hit a little too close to home, as Godfray suggests above. Perhaps be cause no one expects insects to be smart in the first place, or identifies with a bug on a leaf, these biases have not gotten in the way of scientists developing hypotheses about the evolution of egg dumping in insects, another illustration of how using insects rather than vertebrates as models can make it easier to understand behavior.
One's immediate thought is that the dumpee, or host, is a sad patsy here, but unlike the case for brood parasites such as cowbirds or cuckoos, where the host's own offspring virtually always suffer as a consequence of the interloper's demands, egg dumping