Herex

Herex hatch from hard, opaque white eggs about 3 feet across, through which a dark shape can be glimpsed moving shortly before hatching. The larva, 10 to 20 feet long and mottled dun, looks like a squashed, wingless beetle with a large head, strong mandibles, a long flexible abdomen and six short, quick legs. Adults keep this body but have smaller heads and jaws, four slim dragonfly wings and a 5-foot stinger at the tail.

Always hungry, larvae roam the tunnels where they hatched and bite for 2d8. Their acid saliva permanently degrades armor: each bite worsens normal armor by 2 points of AC (plate mail goes from AC 3 to AC 5) and magical armor by 1, and armor reduced to AC 9 or worse dissolves. Protective devices such as rings of protection and cloaks of displacement are unharmed. An unarmored victim instead takes 1d10 extra acid damage.

Adults strike only from the air, diving at foes and landing once the target is dead or helpless. Their bite does just 1d10 but carries the same acid, and their stinger deals 1d6 plus a venom that paralyzes for 4d8 rounds unless the victim saves vs. poison.

Herex have no measurable intellect and live only to breed. They keep no hive and, though clutchmates often stay near one another, are not social. A larva hunts, grows and molts until about 20 feet long, then digs to the surface, chewing and dissolving even solid rock. There it molts a final time into a 13 Hit Dice adult that flies about seeking food and a mate. Males die soon after mating, while females burrow into deep caverns or dungeons to lay 1d6 eggs and die. The eggs hatch in four months.

Kept in a ceramic container, herex saliva eats through almost anything, metal included, and can be used to make universal solvent.