Ants in the home

Order: Hymenoptera
Family: Formicidae

Description

Almost anywhere in Colorado, ants will be the most common insect found in yards, gardens, fields and forests. Most ants found in homes nest outdoors and enter homes to forage for food or water.  Ants are social insects that live in a colony, usually consisting of thousands to tens of thousands of individuals. Within the colony, ants are divided into different castes: workers, males, and queens. Workers are wingless females that forage for food, construct, maintain and defend the nest, and tend the young. Each colony contains one or a few queens that are larger than workers and are dedicated to egg production. Upon egg hatch, the pale-colored, legless larvae are fed and protected by the workers. When full-grown, ant larvae produce a smooth silken cocoon within which they pupate, ultimately emerging as an adult ant. Ant pupae are often seen when turning over a rock that exposes a colony and are sometimes mistakenly called “ant eggs”.  

As colonies mature, winged ants are also produced. These include females that are potential queens and slightly smaller males. These reproductive forms periodically leave the colony during swarming events, when they fly away in large numbers and attempt to mate. Swarming ants can often attract attention and alarm, however, these ants never return to a colony once they have left on a mating flight. Winged ants are sometimes mistaken for winged termites. However, ants can be easily distinguished by having a narrow constriction between the thorax and, antennae that are elbowed, and hindwings that are smaller than the forewings. 

Ants commonly found in Colorado homes:

Pavement ants
Pavement ants (Tetramorium immigrans) arrived in Colorado only in the past few decades, but now are often the most common species that people notice. They produce small mounds of soils at the entrance of their nests and are often located under pavement or rocks. They are small ants that measure 2.5-4 mm (1/10-1/6 inch) long, are dark brown in color and have fine grooves that line their head. Pavement ants forage a wide variety of foods, usually consistently preferring food high in fats.

Problems with indoor ants usually occur in spring and early summer and can be managed with baits, habitat modification, cleaning, proper food storage and exclusion. Outside, pavement ants can be managed with habitat modification, exclusion, and residual insecticides.

For detailed pavement ant management strategies see this factsheet.

Field ants
Field ants (Formica spp.) are commonly found in yards and gardens and are observed in homes most commonly in the spring. They are black or reddish brown and 4-8 mm (1/6-1/3 inch) long. They nest outdoors in loose soil and some produce mounds that incorporate twigs, dried leaves and other plant materials. Field ants feed on a variety of foods but most often are observed visiting sweet honeydew excreted by aphids and or other food sources high in sugars.

Carpenter ants
Carpenter ants (Camponotus spp.) are the largest ants that occur in Colorado at 0.76-2.5 cm (1/3-1 inch) long. And are particularly abundant in forested areas. They may be either black or black with a reddish-brown thorax. Carpenter ants nest in wood and will rarely establish a colony in a building. Nests of carpenter ants may be located by the dust (grass) they deposit while chewing through wood. Carpenter ants feed on a mixture of dead insects and honeydew.

Infestations of carpenter ants usually indicate there is a moisture problem in the house. Carpenter ants prefer nesting in wood with high moisture content, especially when the wood is infested with fungi. Cultural controls of this ant species are centered around reducing moisture in ant-prone areas. This can be achieved by increasing ventilation in crawlspaces, basements and attics, fixing all leaks in the house, using a dehumidifier, and sealing possible entry points in the house.

For detailed management strategies of carpenter ants see this factsheet.

Cornfield ants
Cornfield ants (Lasius spp.) are small 2.5-4 mm (1/10-1/6 inch) long ants that are usually light to medium-brown colored. They nest outdoors but sometimes will enter buildings to feed on sweet materials.

Odorous house ants
Odorous house ants (Tapinoma sessile) are small 2.4-3.3 mm (1/10-1/9 inch) black ants. When disturbed, they will raise their abdomen and emit an odor reminiscent of coconut. They do not nest indoors but may enter to forage on various sweet foods. Heavy mulch adjacent to building foundations has been associated with increased problems with odorous house ants.

Odorous house ants are persistent pests and require appropriate management and follow-up. These ants can be managed by eliminating habitat and contributing conditions and using pesticide baits. Locating foraging trails and nest sites is critical to OHA management. Nest sites and foraging sites are excellent locations to target pesticide applications.

For detailed management strategies of odorous house ants see this factsheet.

Pharaoh ants
Pharoah ants (Monomorium pharoanis) are small, 2 mm (under 1/10 inch) light-brown ants that are adapted to nesting in buildings. Nests can spread extensively through a structure as pharaoh ants may frequently move nest locations, produce multiple queens, and may split to form “satellite” colonies. Pharaoh ants feed on a wide range of foods rich in sugars, fats, and protein. They can be serious pests of hospitals, dormitories and apartments.