Resource management is as much a part of RPGs as combat and spell selection. There is nothing more painful to a player than having to determine what resources to give up when going into a dungeon or what treasure when coming out of a dungeon. Sure, any competent adventurer is going to give up the copper first and only part with the platinum if it is a matter of life and death (and sometimes not even then). But what about having to make the choice of losing a porter (and his carrying capacity) before you go into a dungeon or losing a horse with its food-stuffs and over-land carrying capacity?
And that's why I love ankhegs. They aren't very dangerous to a prepared party or even an unprepared party past about 3rd level. What they are dangerous to is horses, mules, porters, guard dogs and animal companions/familiars. Ankhegs have animal intelligence, meaning they are just as smart as dogs, cats and horses. This means that they can learn to work together, use simple tactics, be trained and create basic ambushes.
Working together, an ankheg pack/pride/flock (I still haven't decided what to call them) could easily create a network of tunnels under commonly traveled areas. This lets them track and evaluate caravans passing through their area - just as African lions, wild dogs and feral boars have been know to do. Remember, they aren't that smart, so don't always have them attack the light armor PCs, but they could certainly learn to not attack the shiny (armor wearing) humanoids in favor of an easy to grab donkey or unarmored porter. They are also only large, so grabbing that halfling mage or gnome rogue might be particularly tempting.
*Blogger deleted about half of my original post, so here's the rest added after the fact.*
Lots of people seem to like using wolves or boars for goblinoid mounts, I like using ankhegs and giant scorpions. The expression on the faces of the players when they realize that the mount is more dangerous than the rider is priceless. And when under control, coordinating a directed acid attack against the heavy armored PC means that either multiple saving throws have to be made, or a fair bit of damage will be done. Not a big deal you say? Well, it's not just the HP of PC that's at stake when a saving throw fails. All that nice, tasty armor, shield, backpack, pouch, weapon, etc. gets to make a save as well. So suddenly, that massive AC that's hard to hit becomes a little less difficult when it's laying in pieces around the PC.
In the newer editions, monster advancement is pretty straight forward. But what's more fun is adding a template and ankhegs are just begging to have a dragon or fiend template applied. Just think about how nice a red dragon template and its fire breath adds to the effectiveness of something that already has a descent acid attack. This also gives them a little more AC and HP to take their time in picking a juicy target.
It is also not out of the realm of possibilities to have them function as a team like a lion pride. And, with their ability to create tunnels, they could certainly trap or funnel prey into designated areas by digging trenches or dead falls along the paths they want their targets to take.