They move fast and fly (long jumps), hard to hit, and they self-destruct on attacking your soldier . . . but, a few turns later, the soldier’s flesh explodes from within as if shot by a rifle and 1-3 worms emerge. If these worms aren’t killed within X turns, they develop into more Botflies. In some missions, you may face swarms of them. (Definitely one mission with a lot of them, like the worm-cleanup mission.)
The model could be like a particle cloud, just a group of flies. Even zoomed in, it would be hard to make out any detail. Viewed close up, though, as on the research screen, they’d look more like a Pandoran version of the bot fly or screw-worm fly, which basically look like honey bees and flies, respectively. You might reference David Cronenberg’s The Fly for what a monstrous human-like evolved fly would look like. Maybe imagine what a Triton would look like if it transformed into a fly like Brundle Fly did in that movie. It would definitely be colorful and have a shellfish-like exoskeleton with mushroom like parts. The head could resemble a mushroom and the belly could look like the “fins” of a mushroom.
They would commonly be found near large amounts of dead bodies, human or animal.
They could be weak to fire and explosions. Acid and poison clouds might also be effective. I imagine targeting the enemy would be comprised of five or six “body parts” with each looking like an individual fly.
There may be giant Pandoran Botflies later in the game, to fight alongside Tritons with grasshopper or flying ant wings. Probably no arms, but there could be variations.