[osr Challenge] Fly on the Wall

Fly on the Wall: A Get Ready, Get Set, Go! Labyrinth Lord adventure set in the Ashford Valley.

Get Ready:
While wandering through the countryside, the PCs encounter a group of Giant Carnivorous Flies attacking a hive of Giant Killer Bees.

Get Set:
The PCs could be looking for a magic cave, resting from being on the run from a previous monster or wandering the wilderness lost. They turn the corner and come face-to-face with a clearing in the woods abuzz with activity.

The flies are attacking the bees and there are several of each on the ground, writhing in their death-throes. Before the PCs know it, they're in the middle of the battling swarms!

Go!:
The swarms are fighting around and with the PCs. What more description is needed? Both sides will pursue the PCs should they run, fighting the whole way.

Notable NPCs:
Giant Killer Bee, No. Encountered: 1d6+4; Alignment: Neutral; Armor Class: 7; Hit Dice: 1/2, Hit Points: 4, 3, 3, 3, 2, 2, 2, 2, 1, 1; Attacks: Sting (1d3 + poison); Save: F1; morale: 9; Special abilities: flight, poisonous sting (stinger breaks off into wound, save v. poison, failure means death, 1HP damage per round until stinger removed).

Giant Carnivorous Fly; No. Encountered: 1d4+2; Alignment: Neutral; Armor Class: 6; Hit Dice: 2d8, Hit Points: 16, 14, 13, 12, 10, 8; Attacks: Bite (1d8); Save: F1; morale: 8; Special abilities: flight, jump 30 feet, surprise on 1-4 on 1d6, immune to giant killer bee poison but not stinger damage.