Fairy flies

"Fairy flies" are some of the smallest insects in the world.

There are about 160 species in New Zealand, about 10% of the world's known species.
Fairy flies are not true flies (Diptera) but actually tiny mymarid wasps (Hymenoptera), which lay their eggs in the eggs of other insects.
All the young stages of the mymarid develop within the host egg, and hatch as adults from the host eggs.
Some fairy flies are less than 0.4 mm long.