by Alan McCoy from Dungeons & Dragons: Fundamentals
How to build challenging
encounters against an Ankheg
Note: This has been prepared utilizing only the 5E Core Rules. The Ankheg can be found in the Monster Manual page 21.
Resembling an enormous many-legged insect, the Ankheg have long twitching antennae that that react to movement around it. Its front legs end in sharp hooks that reach out with extreme speed and grab prey to pull it to their mouth for its powerful bite.
Ankheg are called the “Bane of Field and Forest” by the common folk. These powerful monstrosities are the more than a simple nuisance as they prey upon livestock as well as any larger forest animals that they can find. Pastures of grazing livestock or forests alive with game are prime hunting grounds for an Ankheg. They are particularly during any mating or egg laying season. Unfortunately, these seasons occur at random intervals, though Spring and Summer are most likely.
Ankheg are primarily subterranean creatures. They burrow through the earth leaving behind loose earthwork tunnels. These are often unstable and are also likely to have twists and turns in almost any direction: up, down or sideways, it is all the same to an Ankheg. For those searching there is usually at least one identifiable entrance hole to an Ankheg lair. Do not be misled however, their burrowing speed is such that they can easily create a new exit if necessary.
As an enormous insect, Ankheg most closely resemble a preying mantis, though one of enormous size. They are size category L, which means they are comparable in size to a horse.
Like their small cousins the preying mantis, the Ankheg is an ambush predator, relying on its superior speed to strike and capture prey, unfortunately for their victim, the Ankheg does not always slay its prey before it begins to eat. The bite attack used by the Ankheg is also the first bite of flesh consumed.
There are very few Role Play Aspects that can be associated with an Ankheg, as unintelligent monstrosities they consume to survive and provide for their mate and eggs. Most of the RP elements will concern themselves with the issues of locating and exterminating these powerful pests.
Step 1) Let’s Review what we know about Ankhegs
They have extremely High Strength, above average Constitution and Wisdom, very little intelligence.
Their movement speed (30-foot) on land, but they also have a burrowing speed (10-feet).
Their Senses include Darkvision (60-feet), and Tremorsense (60-feet). They have a passive perception of 11.
Step 2) Determine the probable Strategy
Ankhegs are almost unintelligent, they go where the prey is. If they see prey, they attack. They may hollow out an egg chamber during hatching season, but after the eggs are laid, instinct will force the adult to move on, otherwise it would potentially eat its own hatchlings.
Step 3) Determine Tactics
As stated before, Ankheg are ambush predators, and will often remain virtually motionless until prey is sighted. It then explodes into motion, using its powerful front legs to hook prey and drag them to its mandibles where it can bite.
If the Ankheg finds sustained resistance to its attack, to include cooperative tactics to drive it off, it will retreat into its tunnels. If pursued, it will unleash its ACID SPRAY attack.
Ankheg will often wait a few feet below the surface of the earth using its tremorsense to detect prey of interesting size. It will then burrow and burst out to attack. Based upon it’s clawed front legs, the Ankheg is a capable grappler, and can easily grab and carry off its prey. Once caught, the prey is taken underground where it can be devoured without disturbance.
Fortunately for potential victims, the Ankheg does not take the time to close the tunnel, and leaves behind a unstable, but useable tunnel that can be used to follow it into its lair. The lair is often no more than twenty feet deep, allowing the Ankheg to reach them in a single dash action.
Player Characters who follow will find themselves slowed by difficult terrain due to the rough nature of the tunnel.
Step 4) DM Tips and Observations
The Ankheg is a straightforward beast. Tremorsense and the Acid Spray give it a serious attack in the right situation, but if that can be drawn out of the beast the slow recharge can make this creature a bit easier to kill.
If I were to redesign this creature, I would probably increase its burrowing capability to 15 feet/round, and I’d give the claws a 10-foot reach for grappling, but not for the bite itself.
Because the claw attack is extremely fast, but the Ankheg is slow, I see no need to increase the dexterity of the creature, this can be handled strictly by description.