Grown to monstrous size within the fetid bowels of the most disgusting swamps, giant flies—and their monstrously bloated maggot young—reach sizes of up to 7 feet from their barbed rear legs to their filth sucking proboscises. Although dozens of different types of monstrous flies have been recorded, the most common varieties appear as gigantic, bloodthirsty gadflies. The sickening drone of these disgusting vermin’s flight taints the air as they circle sites of carnage and decay in search of smaller prey and spilled blood.

Ecology

Giant flies follow a lifecycle similar to their minute and infinitely less grotesque mundane cousins. As the hundreds of eggs laid by a female fly hatch, giant maggots are born. These ravenous larvae devour all they can, yet where the centimeter-long maggots of most flies must make do with dead flesh, giant maggots possess the strength and mobility to hunt more lively prey. Rather than flesh-scraping mouth hooks like those of smaller species, giant maggots possess maws filled with rows of spiny ridges, capable of gnawing through even the thickest hide.

Those giant maggots that survive and flourish—for approximately 2 weeks for most breeds—seek shelter or burrow into soft earth to pupate. After a matter of days, gigantic flies emerge, ready to feed, mate, and spawn more of their nauseating ilk.

While normal flies parasitically subsist alongside larger animals, giant flies are consummate predators. Forgoing the stealth of their smaller brethren, these monstrous insects are capable of overpowering creatures up to the size of a horse. Although the numerous varieties of giant fly have vastly differing tastes—some using scissor-like maws to chomp away at live flesh while others favor a slurry of predigested dead meat—these mindless hunters attack any fleshy creature they encounter, regardless of size or apparent strength.

Habitat & Society

Far too large to live among the filth of animals or men, giant flies flourish in places of natural rot or widespread ruin. Bogs and dense marshes sometimes host small swarms of giant flies. Mass numbers of bodies left to rot as the result of a large battle, massacre, or natural disaster sometimes lead to explosions in giant fly populations near such sites, with corpses still serving as a favorite food of the monstrous insects. Unsurprisingly, some of the Outer Planes’ more horrific extremes serve as fetid paradises for giant flies and their larvae.

Variant Giant Flies

Although each of the thousand species of flies do not have their own monstrous counterparts, there are still a number of regional variations between types of giant fly. Listed below are three of the more common ones.

Giant Housefly: Where the giant gadfly uses scissor-like mouthparts to obtain its liquid meal, the giant housefly dissolves its food by retching an acidic slurry over its meal and lapping up the dissolved nutrients. These giant flies are in all ways exactly like the typical version, but their bite attacks deal an additional 1d4 points of acid damage.

Giant Hoverfly: As their name suggests, giant hoverflies have great control over their aerial movement, having a flight speed of 70 feet and perfect maneuverability. Most giant hoverflies resemble giant wasps or bees, but are typically less deadly than those overgrown pests.

Giant Tsetse Fly: With long legs and a pronounced proboscis, the giant brown tsetse fly can be found in various tropical regions. These bloated, mosquito-like vermin spread only sleeping sickness with their bites, although—like typical giant flies—they might spread other diseases as well.