Sickle-flies
An enormous breed of insect native to the Midgewater Marshes of Bree-land, the Sickle-flies and their brood have since begun to spread to other lands of Middle-earth. Whether this is through natural migration or if they are driven by some dark intelligence is unclear. Like the giant Spiders, the Sickle-flies seem to be growing in size and aggression, seeking out new lands in which to multiply and find prey.
For taxonomic purposes, many large flying insects are defined as types of Sickle-flies. This includes the enormous Glowing Fire-flies of Evendim and Eregion, giant Hornets of the Southern Old Forest, Sand-flies of the Cape of Umbar, and various types of Bees and Wasps.
Sickle-flies are found in marshy areas and fields. They are "normal" difficulty and are mostly aggressive, though some threaten to attack. They are weak to Beleriand damage.
Background
Sickle-flies do not appear in the work of J.R.R. Tolkien. They were created for The Lord of the Rings Online. As with Tolkien's giant spiders, the game presumes that many insects and arachnids of Middle-earth are of enormous size.
An index of all known sightings: