Cave Locusts: (from Moldvay)
No. Appearing: 2-20 (1-10)
Move: 60' (20'), fly 180' (60')
Attacks: 1 (bite or bump or spit)
Damage: 1-2,1-4, or special
Save As: F2
They look fairly wimpy individually, and they are. Their low damage and morale means they aren't going to be tearing through a party. Where the locust really shines as an encounter is in its desire not to fight.
First off it will frequently try to flee, but they are extremely clumsy jumpers/fliers. Half the time they collide with a PC, dealing 1d4 damage. If you get a swarm of a dozen or so cave locusts "retreating" at once, odds are good that someone is going to get pummeled.
Another interesting thing that the locust does is spit. A sticky, horrible gob splatters the poor victim. Since the attack is basically "touch" it's versus AC 9, usually hitting. Then the poor recipient must save vs, poison or spend 10 minutes (!) vomiting and being generally awful to be around.
Finally, when the locusts get scared, they whine. This noise can bring down wandering monsters like nobody's business with a 20% chance per round of something showing up to check out the ruckus.
Top this off with NO treasure, and you DMs have a marvelous object lesson for players about why sometimes it's better to leave the monsters alone.
PS - An amusing tidbit: Cave Locusts are immune to most poisons! It comes from eating yellow mold!