Carnivorous worms they sneak into your nest and pillage your food, worker, and soldier larva tiles. Also, they could be a possible method of invasion for enemy ants to sneak in, not saying you cant do it too. It would take precious time to hunt down the worm and block up the holers. But if you leave it open and keep exploring, you could found that the worm has dug to some secret areas where he has died. Say a preserved corpse of an extinct ant species that you can still harvest its DNA from, or an old beer bottle filled with maggots that are feeding on some old food someone put in there, maybe a cavern filled with bioluminescence blue fungus and reanimated scorpions with the fungus that you have to fight, or just fill it with Easter eggs. 
I think it would be an interesting concept to have earthworm holes.
I think it would be an interesting concept to have earthworm holes.