Ankheg

The Ankheg was a huge insect looking monster with many slender limbs and large antennae. It burrowed underground and hunted from below.

Environment
Living in warm climates the ankheg dwelt in partially collapsed burrows usually around 40 feet underground. The ankheg hunted in forests or grasslands where prey would wander in to its trap. And if an area becomes too barren, the ankheg moves on to other, more lucrative areas. Ankheg tunnels were sometimes filled with the remains of victims, eggs or chitin. Their tunnels would sometimes be around 60 to 150 feet long and 5 feet high. Hollow tunnel ends were used for lair purposes, such as sleeping or hibernation.

Combat
The ankheg is a ambush predator that waited around 5-10 feet underground for prey to wander in position. The attack was quick, as the prey was crushed and ground in its mandibles and assaulted with acidic digestive enzymes. If a foe proved too difficult, the ankheg could also squirt acid to take it down. If several ankhegs are attacking a group, the ankhegs would try to attack different targets. If prey was attacked by more then one ankheg, the ankhegs would just play tug-of-war with the unfortunate prey.

Social structure
In a general area could have a lone, pair or a cluster of ankhegs.

Diet
Gaining nutrients from the ground, the ankheg also had to hunt fresh meat to sustain itself. It could also eat decaying meat.

Physiology
Ankhegs have darkvision and tremorsense for 60 feet, and strong chitin armor. The "attack" acid was part of the digestive system for the creature, so it couldn't digest food for 6 hours after after a discharge. Ankhegs that lived in colder areas hibernated during winter. During this time, an ankheg takes nutrients from its shell and its antenna.

Life cycle
Ankhegs mated in autumn when the fertilised female would kill the male to lay 6-12 eggs inside him. Usually, a high number of eggs survive and hatch within two to ten days and start to feed. An Ankheg broodling would not hunt and remains hidden, while its mother would bring it sustenance. After a year, the young would be able to fend for themselves. Around year two, the young Ankheg would shed its chitin before winter. It takes a little less than ten days to complete the process and get a new shell. During this time, the youngling is slower and more vulnerable. To defend itself, it secretes a fluid that smells like fruit rot. This defence could backfire, as some would seek out the smell.

Effect
Ankhegs could prove to be useful for a farmer. Provided it stays alive, its tunnels could bring in water and its excrement has enriching minerals.

Baldur's Gate (video game)
In the Baldur's Gate video game, Ankhegs are a fightable monster. Once killed players can collect the Ankheg shells. Each shell weighs 100 lbs.

Taerom the Blacksmith, in Beregost forges armour from the shells. It takes three days to make. The armour is very nearly as effective as full plate mail, but weighs considerably less and can be worn by classes that usually couldn't wear such heavy armor. Taerom claims to sell ankheg armour to rich nobles for 20,000 GP. If you provide the shell, he will charge just 4000 for a set of completed armour.