Myrmecoleon

A little bit bombardier beetle.  A little bit Vlad the Impaler.  A little bit mythic.  And a lot bit Alien (or Alien³).   The myrmecoleon is an acid-spewing horror that, thanks to its mythic ranks, makes horror movie monsters look easy to kill.  A byproduct of excess mythic energy, myrmecoleons are proof that even the gods have roach problems.

Prince Hadrian has worn the signet ring of his family since his first birthday…and being a ring of regeneration, it has saved his life more than once.  Now it keeps him alive but in utter agony…for Prince Hadrian currently lies speared on the chitinous back of a myrmecoleon after he and his men failed to slay the beast.  Too weak to tear himself off the terrible spike, Hadrian is trapped by his own body as his wounds continually open and reheal.  Adventurers are needed to find the myrmecoleon and retrieve the prince.  The hard part will be collecting him without setting off the beast’s death throes, injuring Hadrian beyond the ring’s ability to repair and dissolving his corpse for good measure.

In a desperate gambit to obtain mythic assistance against a demigoddess of discord, adventurers plant dragon teeth liked seeds in hopes of sprouting udaeoi.  It works—but not before the demigoddess sends insects to devour a share of the teeth.  The insects that eat the teeth then turn on each other, swelling as they cannibalize their fellows until only a single myrmecoleon is left.  Before the adventurers can order their soldiers to march, they must save them from the nightmarish creature.

Adventurers make the arduous journey to Mimir’s Well to seek the soothsayer’s advice.  When they arrive, they find the famous Asgardian sage is no more—a myrmecoleon was drawn to the scent of the decapitated head’s oozing neck stump and devoured him.  Now startlingly intelligent thanks to its repast, it sets a trap for future wisdom seekers.

—Pathfinder Bestiary 4 198

Myrmecoleons come from medieval bestiaries, but they clearly made a wrong turn near H. R Giger’s houses.