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Ants hills range from small mounds of soil to piles spreading over elaborate underground tunnel systems. An anthill might be only a handful of soil or be more than three feet high, depending on its age and the species of the builders. Ants (Hymenoptera) create them as they excavate soil.
Not all ants make ant hills. Certain species live in trees, and soldier ants live their lives on the move instead of in colonies. The ant hill comes from the discarded soil when ants dig underground galleries for their home. Among species that build ant hills, their living space is generally primarily underground. Some species, such as harvester ants, create tunnels and chambers in the hill itself. The earth insulates the tunnels, keeping the habitat cooler in the summer and warmer in the winter than the above-ground temperature.
Many ant hills look like small mounds of soil or sand. An ant hill might have a hole or depression in the middle, making it look like a bull's eye or a crater, with the soil ringing the center. After a rain there may be a pile of mud with small tunnels showing in the center. The anthill may be a shapeless scoop of dirt that doesn't look like a hill or mound at all. Anthills next to sidewalks or buildings often have this unformed appearance. The ant tunnels extend under the sidewalk or foundation, and the only sign is a handful of soil or so.
Certain ant species build ant hills that grow so large over time they may look like ancient burial mounds. Allegheny mound ants create anthills that can rise to a height of 3 feet within two years. They may tunnel 3 feet deep and branch out in a radius of 4 feet. Harvester ants often put pebbles around their nest entrances. Their ant hills form a broad mound on bare ground. They usually have their entrance situated in the southwest side of the mound, according to Colorado State University's website. Leaf cutter ants can create huge mounds to house more than 8 million ants, the Seeds of Change website reports.
Certain species, such as the red imported fire ant, create cone-shaped ant hills. RIFAs usually build their ant hills in sand. The outer layer develops a crust, giving the ant hill a hard surface that holds its pointed shape in place against the elements. The cone size is generally 6 to 18 inches tall by 10 to 24 inches in diameter, the Virginia Cooperative Extension reports. When they build in clay, the ant hills may reach 3 feet tall. The underground chambers may extend 6 feet deep. Although these distinctive structures are a common sign of red imported fire ant infestation, they aren't universal. Their anthills can also be flat.
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