As an professional exterminator, my suggestions differ a little from the others above.
Its important to figure out what kind of ant it is: know your enemy. A microscope and handbook or a ag dept entomologist may be needed to identify the species. Or, take a specimen to pest control company. I do this for people at no charge. Most ants live outside or against/under the structure and send foragers into the house. Ants that would actually nest in a shoe overnight are unusual. In Colorado they could be pharaoh ants or perhaps odorous house ants. Both of these ants are challenges for even the professional. I know Texas has both of the above plus many other problem ants.
Pharaoh ants are extremely small, nearly translucent honey colored. Pray he doesn't have these. Their reaction to pesticide sprays or harsh chemicals like cleaners is to create 100's of new colonies. An infested house can have more than a thousand colonies. An entire small colony could easily live on top of the electrical switch box inside the wall. I found a 3" x 4" x 1/4" plastic container for labels in a desk drawer with an entire colony inside: several queens, larvae, pupae and thousands of workers! If he has these ants he must study if he intends to solve the problem himself.
Odorous house ants are another possibility. The nest could have up to 100,000 ants. They move this nest every 16 days (if I recall correctly) like clockwork. They are bigger than the pharaoh ant and darker. They are speedy and almost chaotic. This ant depends on aphids. They often invade the house after a rain that washes the aphids from the trees.
The absolute best way to solve an ant problem is with bait. Its also the least toxic. It must be slow acting - this means the toxicant must be dilute. Too much toxicant will prevent it from getting to the queens. A dilute mix gives the poison time to work through the colony. If you use boric acid, keep it at less than 5% by weight. Ants can change food preference from day to day. Find something they like. Its hard to weigh 3% of a small amount so you may have to make a lot. Mix thoroughly. Jellies might work for the odorous house ant, but probably won't for the pharaoh. Try peanut butter, pet food, etc.
Commercially available baits are worth a try. The key is whether the ants will take it. If they do, whatever you use will work. Combat granular is excellent, as is Amdro (could be Siege Pro now). I don't think either of these will work on the above ants. Good active ingredients to look for include hydromethylnon, boric acid, and abamectin.
good luck
gobug
