Flies are among the most ubiquitous of all arthropods. They can be found virtually in every habitat but marine environments. Flies hold a pair of membranous wings, however this rule has too many exceptions to be mentioned here. The life history of flies is so richly diverse. There are flies that predate on other insects; there are flies that feed on faeces; others feed on polen and nectar; many of them do not feed at all; there are even flies that feed on oil; there are flies that are scavengers.
There are two suborders within Diptera: Nematocera and Brachycera.
The flies derive from Mecoptera or a related group. Flies have appeared around 240 million years ago (in the Middle Triassic), a bit before the dinosaurs. There is a conservative estimate disclosing one million species of flies on Earth, but roughly 25% is described. So much to be done. There is a world hidden within the fly order.