Reviewed December 1997
Download a free PDF of this guide.
Contents
Related page
Use our feedback form for questions or comments about G7392.
Publication search
Figure 1
Life stages of the ant
Ants are among the most successful insects and are also among the most common pests in and around the home. They may build nests in the soil, in the open lawn, under concrete slabs, stones or boards, and adjacent to foundation walls, in the walls of the house, or in decaying wood or other cavities.
Ants are social insects and live in colonies with three distinct adult castes: queens, males and workers. The immature stages consist of eggs, larvae and pupae (Figure 1). Unlike other social insects, an ant colony may pick up its young and move if disturbed.
Most individuals in a colony are wingless workers. During the year, mature colonies produce winged males and females, which leave the colony in swarms. After mating, the female sheds her wings and attempts to establish a new colony. The male usually dies soon after mating. Queens may live up to 15 years, workers from 4 to 7 years.
The winged swarmer ants are often confused with swarming termites. They are similar in appear ance and both may be triggered to swarm by the same environmental conditions -- often a warm, sunny day following a rain.
Winged ants may be distinguished from winged termites by differences in wings, antennae and "waist." See Figure 2 for comparisons.
Figure 2
Comparison between ant and termite.
Ants feed on a variety of foods such as sweets, starches, greases, and other plant and animal materials. Some species feed on a substance called honey dew, which is secreted by aphids. These aphids may be tended on plants and cared for by the ants. In this relationship, the aphids are referred to as "aphid cows."
Almost all ant species feed on secretions from their own larvae. Adult ants are restricted to a liquid diet. They may appear to eat solids but are merely squeezing the liquid from the food.
Sugar granules may be dissolved in liquid and then imbibed. In some species, the larvae are capable of eating small particles of solid food. The search for food is the primary reason ants enter buildings and become pests.
The activities of most ants do not adversely affect humans. Those that prey upon other insect pests are considered beneficial. Many ants are capable of stinging and some, such as the fire ants in the southern United States, are severe threats to humans.
Some ants damage desirable plants by stealing seeds, chewing on the plant, and fostering injurious insects such as aphids. The presence of ant mounds may be undesirable in locations such as lawns, parks and golf courses.
The most common conflict with man, however, is when ants invade the home in search of food. In so doing they may contaminate food and become pests simply by their presence.
About 100 different species of ants occur in Missouri. About one-fourth of these may enter homes, but only about a dozen are common house pests.
Table 1
Some common ant pests of homes in Missouri.
| Name | Color | Size of worker | Foods | Common nest locations | Comments |
|---|---|---|---|---|---|
| Acrobat ant Crematogaster spp. | Yellowish brown to black; abdomen usually darker | 2.5 to 4 mm | Sweets, meats | Decayed wood; under stones; behind house veneers | Heart-shaped abdomen often raised above thorax; will sting and bite; invades homes for food only occasionally. |
| Black carpenter ant Camponotus pennsylvanicus | Usually black but may be partially reddish brown | 6 to 12 mm | Sweets, meat, grease | Partially decayed wood; natural cavities in wood or other objects either inside or outside | Doesn't eat wood but hollows it out to form cavity for nest. Sawdust and other debris kicked from nest often marks nest entrance. |
| Cornfield ant Lasius alienus | Brown to blackish | 2 to 2.5 mm | Sweets, meat | Rotten wood; under stones and sidewalks; in the soil in open areas. | Normally outdoors where it may produce many small mounds in the lawn; a common "picnic" ant. |
| Crazy ant Paratrechina longicornis | Dark brown | 2 to 2.5 mm | Sweets, meat, grease | Small crevices inside buildings | Has long legs and antennae and tends to run aimlessly about, accounting for its common name. |
| Field ant Formica spp. | Red, brown, black or combinations of these | 3 to 7 mm | Sweets, meats | Outdoors in the soil along fences, sidewalks, flower beds | There are several species in this group that are normally outdoors and only occasionally enter homes for food. Some are mound builders. |
| Honey ant Prenolepis imparis | Light to dark brown | 3 to 4 mm | Sweets | In soil in shady areas | Some individuals feed until their abdomens become greatly distended and they in turn feed other individuals by regurgitation. |
| Larger yellow ant Acanthomyops interjectus | Yellowish to reddish brown | 4.5 to 5 mm | Sweets | Old logs; stumps; under stones; along house foundation | When crushed, give off a pleasant citronella odor. Are often confused with termites when they swarm adjacent to houses. |
| Little black ant Monomorium minimum | Shiny, jet black | 1.5 to 2 mm | Sweets, meats, grease, fruit, vegetables, bread | Rotten wood; under rocks; in masonry; in soil | Normally nests outdoors but readily adapts to the household situation. |
| Odorous house ant Tapinoma sessile | Brownish to black | 2 to 3 mm | Sweets, meats | Beneath boards or stones outside; almost anywhere inside the house | When crushed, give off foul odor. Invade homes especially during rainy weather that washes away their primary food, honeydew. |
| Pavement ant Tetramorium caespitum | Brown to blackish brown; legs and antennae paler | 2.5 to 4 mm | Grease, seeds, meat, sweets | Under stones, pavement, sidewalks; adjacent to house foundation; occasionally in walls of house. | Head and thorax furrowed by parallel lines. |
| Pharaoh ant Monomorium pharaonis | Light yellow to red | 1.5 to 2 mm | Sweets, meat, grease | Wall voids; behind baseboards; other small voids | Very large colonies. Often pests in hospitals and will feed on human wounds. Colonies often break-up into several colonies. |
| Thief ant Solenopsis molesta | Yellow to dirty brown | 1 to 1.5 mm | Grease, meats, sweets, seed | Cracks and crevices of cabinets and walls | One of our smallest ants. Often lives in the nests of larger ants, stealing and feeding on the larvae of the hosts. |
The key to controlling most ant species is to locate their nest and apply an appropriate insecticide. Ants usually follow a definite path, marked by pheromones, from their nest to the food source and back. By observing and following this path, one may discover the nest site. Most ants nest outside the house in the soil or adjacent to the soil under various objects.
The pharaoh ant is an exception that nearly always nests indoors. Carpenter ants and the odorous hose ant are also exceptions that readily nest indoors as well as outside.
Carpenter ants hollow out dead and decaying wood to build a nest, or they may simply use an existing void in the building construction. Since they differ considerably from most house-infesting species in their biology and control, they are covered separately.
If the nest is not found, spray windowsills, door thresholds, and other openings, baseboard, behind and under cabinets and appliances, and other surfaces. Ants should be killed as they crawl over sprayed surfaces.
Since only the worker ants are killed this way, retreatment may be necessary. One must continue to kill workers until none are left. Individuals back in the nest starve to death when there are no workers to feed them. Table 2 lists the insecticides for use indoors for ant control. Do not contaminate food or utensils and do not spray food preparation surfaces.
Various baits available in ready-to-use containers can be effective if enough containers are used and properly placed. Other baits may be purchased in a form such that variable amounts may be placed where desired. The use of baits is usually very effective in controlling the odorous house ant.
The pharaoh ant is particularly difficult to control. It is most often found nesting in the walls or other locations in institutional buildings such as hospitals and schools. It may also be found in individual homes. Conventional spraying of premises will often cause the colony to break up into several colonies that relocate, thus increasing the problem rather than eliminating it. Baiting is the most effective way of controlling this pest. If the problem persists, hiring a professional pest control operator is usually advisable.
Table 2
Ant control insecticides for use indoors.
Note
Insecticides listed in this table for use only by professional pest control operators; may or may not be superior to those available to the general public.
For nests in the lawn, adjacent to buildings, or other outdoor locations apply the insecticide to the nest openings and over the area surrounding the nest openings. Where nests are not found but ants are coming into the structure from outside, a perimeter spray may be effective. Spray the foundation from the ground up about three feet and the ground from the foundation out about three feet. Be sure to spray well around all doors and basement windows. Table 3 lists insecticides for outdoor application.
Table 3
Ant control insecticides for use outdoors.
G7392, reviewed December 1997