The research into moth-based B.O.W.s was a failure in this experiment. Mutating to a larger size normally did not keep them in proportion, making their wings strong enough only to hover over the ground. However, they did also develop the ability to spit poison on prey as a means of compensating for their flight problems.
Resident Evil 2
Use the grenade launcher, preferably with incindiary rounds or shotgun against it. If playing as Leon using the flamethrower one may burn her wings off and simply avoid the crawling body.
If you aren't playing with Yoko, use the shotgun against it because you will be captured and poisoned if the moth isn't killed. Yoko also needs to kill the moth in harder difficulties because the poison drains your health quickly.
Ignore them. If you wanna fight, use the shotgun and pay attention to not be attacked by the other one.