Colorado is home to two species of harvester ants, the western harvester and the rough harvester.  Their mounds are broad and flat with areas of vegetation cleared surrounding them.  These mounds are highly visible and cover a network of below ground tunnels which are utilized by the colony.  Small pieces of gravel are often incorporated into the mound as they are excavated from inside the tunnel systems.  Cleared vegetation prevents the mound from being shaded, which allows the sun to warm the nest.  Nest entrances typically point to the southwest.  Harvester ants are a grassland species with the western harvester being common to the eastern plains, San Luis Valley and the grasslands of western Colorado.  The rough harvester ant is more restricted, being found mostly in southeastern Colorado.

In general, harvester ants are moderately large, measuring 5-7mm in length.  Feeding primarily on seeds, harvester ants will also occasionally gather dead insects.  They have relatively large heads and powerful jaws that are needed for cracking seeds.  Western harvester ants are reddish-brown in overall color, while the rough harvester ants have a black head and thorax.  If nests are directly disturbed, harvester ants will forcefully defend their mound.  Disturbed mounds will resemble army like activity within a very should time. Bites as well as stings are common when this occurs.  Stingers although present are short and lack the ability to penetrate areas of thick skin or clothing.  When stings do occur they are very painful.

Reproduction occurs in the form of swarms of winged reproductive (males and potential queens).  These swarms are most common during the summer months within a few days of heavy rain.  Swarms are known for seeking out a prominent feature of their surrounding landscape (hilltop, housetop, tall buildings) in which to swarm.  During these mating flights, it is not uncommon for a ball of mating ants to fall down a chimney or other vent, into the home.  Males will die within a 24 hour period while newly mated females begin the search for a new location for her colony.  She breaks off her wings and utilizes nutrients from her no longer needed flight muscles to sustain her until her colony becomes established. Queens may live for more than a decade, with her colony increasing in size.

Harvester ant workers can live for long periods of time and are easily maintained in captivity which results in them being commonly utilized in certain forms of ant farm displays.

Western Harvester Ants in an ant farm

Western Harvester Ants in an ant farm