Family Cecidomyiidae
This family of flies are characterized by their size as they are very small, typically no bigger than 2-3mm in length, and a large majority are smaller than 1mm. Their name, Gall Midges, refers to their larvae which are laid between plant tissues and will feed. This creates abnormal growth in the plant called galls that protect the larvae.
A unique trait these insects have is they can reproduce before adulthood. This is know as paedogenesis, and can result in some larva being eaten by their own progeny. These insects are usually considered pests as they can be very destructive to crops like wheat. Though they are certain species that are very beneficial pest control, for example Aphidoletes aphidimyza is sold across the US as a biological control for pests like Aphids.