"You don’t encounter Mumbo swarms often, but in those rare instances, expect to find them in lava-filled rooms. They don’t offer much in the way of threats and can be easily disposed of, but that doesn’t mean you should ignore them. They often fly in a path that crosses right into yours."
Walkthrough (p. 98)
"These pack animals are rare and generally harmless unless you get in their way. Like other swarming enemy types, Mumbos are excellent sources of health, Aeion, and ammunition. Turn on your Lightning Armor and melee away to obtain an abundance of resources."