The norm is for insects to lay eggs, ranging from 2–5 in the large dung beetles to 750,000 in the peculiar, bee-parasitising Strepsiptera. But a small number of species have made the fairly simple jump to viviparity (laying live larvae or nymphs).
The best known are aphids, whose complex life-cycles include a phase of generating live nymphs that already contain developing embryos. This all-female cloning allows for rapid colony growth in times of plenty.
A few blowflies are larviparous (the eggs hatching inside the female shortly before they are deposited), giving the maggots a head-start in frenetically competitive micro-habits such as dung or carrion.
The blood-sucking tsetse flies of Africa have taken this to the extreme. Each female broods a single egg in her abdomen, and when it hatches she feeds it protein-rich secretions in an organ analogous to a womb. Only when the larva is fully grown does she lay, at which point her offspring pupates into the chrysalis stage to change into an adult.
Main image: a black aphid Ⓒ David Spears /Getty Images
