The female green spoonworm keeps the male in its place (Image: Biosphoto/Dino Simeonidis/Still Pictures) A mother pygmy marmoset carries her two babies on her back (Image: Edwards/Newspix/Rex Features)

ONCE upon a time, sex in the animal kingdom seemed pretty simple. Flamboyant male met coy female, male courted female, male deposited spermatozoa in the vicinity of an ovary, then headed out to do it all again elsewhere.

Then biologists began to look more closely, at what really happens. They found that being the biggest and brashest male doesn’t always win you mating rights. Among weaver fish, for example, it is good fathers, the ones who will take care of the fry, who get the girl. Females don’t always conform to type either. The female bean weevil, for instance, would rather drink her mate’s ejaculate than use it to fertilise her eggs. Reproduction, it turns out, is a complex affair.

Just how complex has been emphasised anew with a slew of studies that highlight the staggering diversity of sexual practice in the animal kingdom. Intercourse is a bizarre and often dangerous pursuit, where sexually transmitted infections can be desirable, living in a male harem inside your mate can make sense, and headless lovers give you extra. Relations between the sexes are also surprisingly convoluted. Biologists have charted virgin births, spontaneous sex changes and, perhaps weirdest of all, males who father their brother’s offspring. Human sexual exuberance is tame compared with some of the things that animals get up to in the name of reproduction.

Take the male praying mantis, the poster boy of risky sex. In an ideal world, he will jump …