Cave Grubs

From Introduction:

The things that adventurers call cave grubs look like angry, mutant crickets, but may turn out to be a welcome encounter for those lost beneath the earth and starving for any scrap of food they can find. For these weird bugs have adapted themselves to feeding off magical ores and fungis in caves deep within the mythic underworld. Just as they scrounge for food in these awful, lightless caverns, so too can larger creatures use them for food in turn. Such a diet, however, does not come without its consequences, for the subterranean
environments the cave grubs dwell in are rife with chaotic magic that builds up inside their bodies and then flows upwards through the food chain.