An aphid can be born already pregnant

In the summer generations, a female aphid gives live birth to daughters who already contain embryos. A grandmother, a mother, and a granddaughter are nested in one body.

Many aphids spend the warm months as a clone of females, producing young without males. The young are born live, not as eggs, and development is telescoped: an embryo begins to grow her own embryos before she leaves her mother. Dissect one and the nesting is visible. It is how a single female on a rose bush becomes a crowd before the season turns. The biology is ordinary entomology. The consequence is a population that does not so much reproduce as unpack.

The trick is seasonal. In autumn, for a great many species, the line switches. Males appear, mating happens, and the winter is passed as a fertilised egg, one generation at a time, on a woody host. The nested pregnancy is the summer machine, not the whole life cycle, and not every aphid species runs it the same way. Where it runs, the body you see is three generations deep, and only the outside one has legs.