Male decorated crickets (Gryllodes sigillatus) and katydids (bush crickets, family Tettigoniidae) provide a nuptial gift to females called a spermatophylax.
As with many nuptial gifts, it’s something for females to eat during the process of sperm transfer; once the female has finished feeding on the spermatophylax, she detaches the sperm-transferring organ and consumes that too – putting an abrupt end to sperm transfer.
The spermatophylax is a gift that is physiologically synthesized by the male and doesn’t seem to benefit the females in any way.
The existence of the spermatophylax is somewhat puzzling to biologists. It’s composed largely of water and free amino acids, but studies have shown that females are unlikely to experience any nutritional or physiological rewards for consuming it.
Males alone benefit, because they significantly increase their chances of successful fertilization by providing it to females.
The amino acid composition of the spermatophylax is a critical factor in determining how much of it will be consumed by the female.
In decorated crickets, females discard the spermatophylax and prematurely halt sperm transfer in approximately 25 per cent of cases.
When researchers examined the components of both desirable and undesirable gifts, it was found that components that induced a positive “gustatory” response in females were preferred. In other words, when males made their speratophylaxes really delicious, females spent more time eating them – regardless of the fact that they were not conferring any nutritional benefit.
Affectionately termed the “candy-maker” hypothesis, this type of behaviour is widespread in all cricket and katydid species that produce spermatophylaxes. It appears the spermatophylax is not so much a gift as a sensory trap designed to maximize sperm transfer.
This post is an adapted excerpt from my book “Wild Sex: The Science Behind Mating in the Animal Kingdom“