They rarely come alone. They march single file through miniscule cracks around windows or under doors, looking for crumbs, water or a warm place to make a new home. Often you'll see them trooping up your walls or across your counter, organized and on a mission. You have an ant invasion.

But what kind of ants have taken over your home? There are nearly 16,000 identified ant species and subspecies, according to AntWeb, an online ant database published for the scientific community. But scientists discover new species all the time, so that number keeps going up.

The good news is that any particular state in the U.S. is going to only have a few hundred ant species, says evolutionary biologist and entomologist Corrie Moreau, Ph.D., associate curator of the Field Museum of Natural History in Chicago where ants are the main focus of research in her lab. The even better news is you're only likely to find a handful of those species in your kitchen, she says.

But if an ant finds something interesting on your counter, you better believe word will get out.

"They're highly organized. If an individual finds a food source, they'll go recruit the sisters in their nest and march back and find it," says Moreau. "Ants rely on communication through chemicals or pheromones. They lay a pheromone trail."

And hundreds or thousands of ants will line up to follow that trail to see what goodies are waiting in your house.

Here's a look at some of the more common ants you might find marching around your home.

Odorous house ants

odorous house antThe odorous house ant will often come marching indoors looking for food. (Photo: Brian Gratwicke/flickr)
These small dark brown or black ants are one of the most common ants found inside homes. They're often found on counters or running along floorboards. They'll come inside looking for food or someplace dry during rainy weather. They earned their unusual name because of the odd smell they give off when crushed. Some say it smells like blue cheese or something rancid, like rotten coconut. They love sugary foods, as well as dead insects.

Pavement ants

pavement ants eating honeyPavement ants feast on some honey. (Photo: Fractality/flickr)
These aptly named insects make their homes in sidewalks and under rocks, coming indoors when they're foraging for food. Like most ants, they're fond of sugar, but pavement ants also like greasy foods and meats. "These are one of the few ant species that will actually have battles to the death," says Moreau. "If you were to get down on your hands and knees to watch them, you'd see lots of dead ants lined up there." The ants will return to the battleground over and over until a colony has established dominance. Typically they'll go to war in spring and summer, and that's also when you're more likely to find them in the house, sometimes in the basement.

Ghost ants

ghost ants eating an appleGhost ants feed on a piece of apple. Can you see them? (Photo: Sarefo/Wikipedia)
The ghost ant gets its name from its very pale legs and abdomen, which can make it very hard to see. The rest of its body is usually dark. Like odorous house ants, they give off a rancid smell when crushed. They're most common in Florida but can survive when accidentally transported to northern states if they take up residence inside heated buildings. They often come inside hunting for sweet snacks and will live in baseboards and flower pots.

Carpenter ants

carpenter antIt's not usually good news when you see carpenter ants inside your home. (Photo: Sancho McCann/flickr)
These are among the largest ants in the U.S., and are typically dark brown or black. The good news, says Moreau, is that "most species of carpenters ants have no intention of being associated with your home. Very few species will live inside human homes. Unless you're seeing carpenter ants come in and out of the framing of your doors, you really have nothing to worry about." But if you've seen these insects inside, it's not usually a good sign. They like to nest in decaying wood. Although they don't cause the damage, they will capitalize on it and can cause the wood structure of your home to weaken.

Rover ants

Have you ever done a double take when you've seen a crumb moving across your counter? Likely the cause of its locomotion was a tiny rover ant. These itty-bitty insects (as small as one-sixth of an inch) can range from dark brown to pale blonde and may congregate in large numbers inside on the top of your sugar jar or the lid of your honey.

Argentine ants

Argentine antsArgentine ants swarm around one of their fallen friends. (Photo: Matthew Townsend/flickr)
Also known as sugar ants, Argentine ants are typically found in the U.S. along the coast of California. They aren't native here, but were accidentally introduced from Argentina and now form giant super colonies, according to Moreau. Argentine ants are typically medium-sized and dark brown and usually nest outside. "But they love to take advantage of sugar sources or crumbs you leave in the kitchen and sometimes will come in looking for water," she says. There may be times when you see large numbers of the ants indoors and then times when you don't see any around. Often they come inside in spring when it's rainy and they're looking for dry places to move their homes.

Fire ants

fire antsSmall red fire ants are aggressive and can deliver a nasty bite. (Photo: SweetCrisis/Shutterstock)
If you live in the South, you've likely seen these small red ants in the driveway or in the grass. You'll know they've bitten you when you feel their sharp, fiery sting. Fire arts build mounds outside and like to stay in hot, sunny areas. But these aggressive insects will occasionally come indoors looking for food and water.

Crazy ants

These insects earned their name for the erratic way they move. Instead of marching in a line like most organized ants, crazy ants move in a non-predictable pattern. These ants are reddish-brown and about one-eighth of an inch long and are most common in Texas, Florida and throughout the South. They have a taste for sugar — and electronics — as they like to nest in circuits and wires to keep warm. If you have a crazy ant infestation, you'll likely know it, as this New York Times story reports. Thousands of ants will crawl over heaps of dead ants. (It will make you itchy just reading it.)

Keeping ants outside

"I love ants, but even I want to discourage them from coming into my home," says Moreau. She suggests keeping areas clean by wiping counters and floors and making sure there aren't crumbs. Don't keep pet food sitting out and clean up after your dog or cat eats.

Pesticides aren't typically a great idea, she says. If you spray or put down bait, you'll only kill the ants that encounter it.

"Unless you have a method to get that poison all the way back to the nest, you're going to keep having recurring individuals showing up," she says.

Instead she suggests caulking around doors and windows and spreading fine powders like cinnamon or corn starch where you've seen ants enter.

"Almost all insects have fine hairs on them and the fine powder gets stuck in their hairs and they don't like it," says Moreau. "It won't kill them, but it's such a pain for them that they'll go to your neighbor's home instead of yours."

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Mary Jo DiLonardo Mary Jo writes about everything from health to parenting — and anything that helps explain why her dog does what he does.