Hellish mosquitoes swarm

Alone a hellish mosquito does not differ of a classical mosquito: he makes this awful sound that won’t let you sleep; he pierces your skin to consume blood rending the place nub at the moment, and left you with an overwhelming need to rub your skin where he drank.
But when they gather in swarm, they choose a target, can inject enough venom to render him motionless, drink all his blood, lay their eggs in his dead body and choose another prey to do it again until their **** at the end of the day. The next morning the eggs will hatch and new swarms will ravage the world.
Be warry using it, a revocation spell will only revoke the mosquitos; don’t forget to burn the body of the victim to prevent eggs to hatch.