Lavaworm

A lavaworm looks like semimolten rock, dull brown or red, up to 5 feet long and 9 inches thick, and inches along on elastic skin. Each end has a needle-toothed maw and two eyes, so it seems to have no rear, though the back mouth is smaller and it never travels backward. Both mouths vent sulfur-reeking gas.

It attacks any moving thing cooler than itself. Every five rounds it can surge at movement 20 for 1d4 segments, always gaining surprise. The front bite does 2d4, half of it heat; the rear mouth bites only when the front does, at -3, for equal damage. Every five rounds it also belches a sulfur cloud that blinds all within 20 feet for 1d6 rounds unless they save vs. breath weapon, and a blinded character can fail again and add more blindness.

Lavaworms eat only cooler creatures and leave fire elementals and other beings at least as hot alone, except when seeking somewhere to lay eggs. A female deposits her eggs on the hottest spot available, often an efreeti, a helian or another lavaworm, since hatching needs intense heat. Around 500 hatch, tunnel into the host and devour it, usually killing it fast, then eat each other until a week old and leave as half-Hit Die monsters. They gain half a Hit Die monthly and mature at one year.

A male mates with as many females as he can find over seven days, then becomes permanently sterile; females breed yearly all their lives. Sterile males claim territories empty of other lavaworms and defend them to the death, so a lone lavaworm is nearly always one of these. Reports speak of some 20 or 30 feet long with maws 4 feet wide.