Mosquito

The mosquito is a mosquito. It was killed by Genos.

Appearance
It looks like an average mosquito you would usually see with wings and a stinger.

House of Evolution Arc
Saitama is watering his cactus, as a mosquito lands on his arm. Saitama attempts to kill the mosquito by slapping it, but the mosquito flies up unharmed. This angers Saitama, as he stands up attempting to kill it again, and again.

The mosquito's last appearance is seen as it is flying away from Saitama, who is attempting to spray it with some bug spray. Genos warns Saitama about the large swarm in front of them, Genos uses his Incineration Cannon to destroy the swarm, killing all the mosquitos in sight.

Abilities and Powers
Despite having looked like a normal mosquito, it was able to swiftly evade every single of Saitama's attempts to kill it. This is such a impressive feat that nobody so far has ever replicated. However; it is most likely that Saitama being unable to swat it is a gag scene.

Physical Abilities
Flight: Like all mosquitos, it possesses wings that allow it to fly.

Specialized Proboscis: As a mosquito, it possesses a proboscis that it uses to puncture the skin of their prey and suck out their blood for sustenance.