Polyembryony

Polyembryony is the phenomenon of two or more embryos developing from a single fertilized egg. Due to the embryos resulting from the same egg, the embryos are identical to one another, but are genetically diverse from the parents. The genetic difference between the offspring and the parents, but the similarity among siblings, are significant distinctions between polyembryony and the process of budding and typical sexual reproduction. Polyembryony can occur in humans, resulting in identical twins, though the process is random and at a low frequency. Polyembryony occurs regularly in many species of vertebrates, invertebrates, and plants. 

Armadillos are the most well studied vertebrate that undergoes polyembryony, with six species of armadillo in the genus Dasypus that are always polyembryonic. The nine banded armadillo, for instance, always gives birth to four identical young. There are two conditions that are expected to promote the evolution of polyembryony: the mother does not know the environmental conditions of her offspring like in the case of a parasitiods, or a constraint on reproduction. It is thought that nine banded armadillos evolved to be polyembryonic because of the later.

A more striking example of the use of polyembryony as a competitive reproductive tool is found in the parasitoid Hymenoptera, family Encyrtidae. The progeny of the splitting embryo develop into at least two forms, those that will develop into adults and those that become a type of soldier, called precocious larvae. These latter larvae patrol the host and kill any other parasitoids they find with the exception of their siblings, usually sisters.

Obligately polyembryonic insects fall in two classes: Hymenoptera (certain wasps), and Strepsiptera. From one egg, these insects can produce over thousands of offspring. Polyembryony wasps from the Hymenoptera group can be further subdivided into four families including Braconidae (Macrocentrus), Platygasteridae (Platygaster), Encyrtidae (Copidosoma), and Dryinidae.

...
Wikipedia