Fairyfly

Family Mymaridae — the fairyflies — contains about 1,400 species worldwide and includes the smallest known insects on Earth. Most fairyflies are 0.5-1 mm long and parasitize the eggs of other insects (especially leafhoppers, planthoppers, and beetles); they are extensively used as biocontrol agents in agriculture. Dicopomorpha echmepterygis (described by Mockford 1997) holds the record for smallest known insect: adult males measure just 0.139 mm (139 microns), smaller than a single Paramecium aurelia (a single-celled organism that is roughly 250 microns) and smaller than many single-celled organisms. The males are blind, wingless, and incapable of leaving the host egg in which they develop; their entire adult life consists of mating with the female fairyflies that emerge from sister-eggs in the same host clutch (an extreme case of inbreeding within a single host). The males are SMALLER than the female sperm cells of some larger animals. The closely related Kikiki huna (described from Hawaii in 2007) is the smallest FREE-FLYING insect at 158 microns. The brain of these microscopic Hymenoptera contains around 7,400 neurons (versus 100,000 in fruit flies and 86 billion in humans), is so small that the cell bodies extend into the wings and legs, and is the smallest nervous system of any free-living animal yet measured. Despite the absurd small size, fairyflies are fully functional animals: they fly (when winged), see, mate, and reproduce.