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it comes to sexual activity and allowed them to either mate as per usual, or mate with a freshly killed female, something they did quite readily. She also starved some of the males so that they would seem to the females to be of poorer genetic quality than the others, and then compared how many sperm were transferred to the female's reproductive tract. Not surprisingly, the food-deprived beetles were less successful at transferring sperm—but only as long as they were mating with a live female. Males mating with the dead, and hence incapacitated, females showed no difference in their ability to inseminate, regardless of their condition. This means that the female herself must be doing something to influence the father of her offspring, favoring the well-fed and presumably higher-quality males.

Other, perhaps not quite so ruthless, experiments used anesthetized female flour beetles to study the degree to which females can control the movement of sperm inside their bodies. The immobilization of a female's musculature caused changes in the number of sperm inside different parts of her reproductive tract, further supporting the idea that females are more than simply vessels for sperm. A similar experiment was performed using a small moth; when a female moth was mated to two males, the larger individual always fathered most of the offspring, regardless of the order in which the matings took place. Again, this bias seems to be due to the female's actions, because anesthetized females showed no sperm in their sperm storage organs, even though the sperm themselves were just as mobile as ever, suggesting that the female has to actively shuttle sperm into the right place.

Among most vertebrates, sperm are deposited all at once during ejaculation, which means that the length of copulation probably has little effect on the number of sperm transferred. Many insects, however, transfer sperm in tiny packets, called spermatophores, that often attach to the outside of the female's body, leaving them perilously vulnerable to removal while the sperm are draining into the female's reproductive tract. Other species transfer sperm during the entire mating process, which can take many minutes or even hours. This means that if females control how long coupling lasts, they also control how many offspring a given male is likely to father. For example, female black field crickets in Australia let spermatophores remain attached longer for more attractive males (those singing more energetic songs) than for relatively wimpy males.

To induce females to allow spermatophores to remain attached, males in many different insect groups offer an enticement in the form of food. Several different kinds of male katydids produce not only the spermatophore like those of the crickets discussed above, but a nutritive blob attached to it called a spermatophylax. In some katydids, this structure takes several days to manufacture, and weighs a third or more of the male's body weight, representing a substantial offering. The female eats the spermatophylax, and its protein-rich contents enable her to lay more and larger eggs. The sperm are transferred to the female while she is eating the spermatophylax; when she has finished her meal, she often reaches around, breaks off the sperm-containing structure, and eats that too. The larger the spermatophylax, the longer it takes her to finish it, and therefore the more sperm enter her body.

Because the spermatophylax is so expensive to produce, each one represents a significant chunk of the male's mating effort for his lifetime. As a result, males in some katydid species become rather choosy about just who is entitled to receive one of the delectable morsels. Larger female katydids lay more eggs, which means more offspring sired by a male's sperm. Thus, as might be expected, in Mormon crickets (which are really katydids, not crickets, and which lack any religious affiliation so far as anyone can determine), males spurn small delicate females in favor of plump ones, a practice that may console failed dieters.

Other insects,