Putting “blood” in front of a noun is practically cheating when it comes to monster names, but damn does it work wonders in the blood caterpillar’s case. That’s a terrifying juxtaposition, particularly when the result is the size of a horse, deals Strength damage when attacked, and feeds on rotting flesh.
“Horn caterpillars feed on the hooves and horns of dead ungulates,” says Bestiary 5. Which means that they should be at the top of pretty much every GM’s list of low-level monsters.
One of the ways fantasy role-playing falls short in the verisimilitude department is that we don’t pay nearly enough attention to livestock. Cattle matters to the pre-modern world, even a magical one. The Táin Bó Cúailnge was sparked by a cow. Half of Heracles’s labors involved one farm animal or another. The defining crime of the bad guy in a Western? Cattle rustling.
So in any halfway “realistic” fantasy world, a monster that feasts on the hooves and horns of cattle and other livestock should be a pretty common nuisance. Clearing out a clutch of horn caterpillars that have taken over the local slaughtering yard might be the first unglamorous job for many a would-be adventurer.
Just on the cusp of adulthood, a band of young friends is charged with escorting their clan’s dead to the traditional resting place, a network of deep caves. Unfortunately, a clutch of horn caterpillars now infests one of the chambers near the surface, feasting on the offerings of antlers and horns left there by clan shamans.
Adventurers accompany a local celebrity, a renowned halfling sellsword, to the Moot at Highbarrow. Spotting the telltale signs of battle and cobwebs strewn in the road along the way, he takes a detour to hunt giant spiders—a callback to the ambush that made him famous. Only the cobwebs aren’t cobwebs; they're caterpillar silk…and the halfling’s famed magic sword carries no enchantment against other vermin.
High on their success defeating goblins, some fresh-faced party adventurers soon find themselves out of money and hurting for work. They’re forced to take jobs at the local abattoir rooting out a horn caterpillar infestation…and then they come across a corpse that isn’t bovine.
—Pathfinder Bestiary 5 51
Achieved escape velocity, finally home in Maryland.