Giant Tsetse Fly

This blood-sucking fly, the size of a horse, is widely despised as a harbinger of disease. Giant tsetse flies rarely congregate in large numbers, as they require gallons of blood each day to survive and thus crowd out or drive away rivals. Any group of creatures large enough to sustain multiple tsetse flies, such as a herd of dinosaurs, are quite likely to dominate the surrounding ecosystem on their own right.

A single giant tsetse fly can kill an entire herd of large animals within a few weeks, and those they don't kill often succumb to disease. When not hunting, giant tsetse flies prefer to hide in warm, dark places in forests and swamps, though they sometimes inhabit wet cave systems where prey is plentiful. The thrumming drone of their wings echoes around such cave systems, warning travelers familiar with the noise that the creatures are lairing nearby.

If food becomes scarce, a giant tsetse fly relocates elsewhere. They tend to follow rivers, animal tracks, or even roads to find food. This can take them to the fringes of civilization, where farms and ranches often have livestock that draws their attention. Settlers who find evidence of a giant tsetse fly should quickly seek out help to eliminate the pests, as all their animals (and, indeed, their families) are in jeopardy as long as the hungry insect is near.

Giant tsetse flies are only moderately smarter than ordinary flies, but some creatures have learned that they can train the creatures with frequent offerings of fresh blood. Giant tsetse flies might therefore be put to use as guardians or even mounts, but any potential trainer must take care not to become the voracious insect's next meal.