Thatching Ant

Thatching Ant


Thatching ants are sometimes referred to as mound ants because some species construct mounds from small sticks, grass stems, leaves, and pine or fir needles. They may also nest in decayed logs. Under most circumstances, thatching ants should be considered beneficial, since they are fierce predators of other insects.

However, where they occur in lawns, rockeries, picnic areas, and other locations of human habitation, they can become a severe annoyance. Additionally, they are often injurious to seedling trees or plants near their nests, and they have been known to damage the buds of apple, pear, and plum trees in the spring.

The landscape can be visually disrupted by the presence of their mounds. Physical contact with them is also displeasing, since they can bite quite hard and usually spray the area they have bitten with formic acid to produce a painful sensation or even blistering if the skin is not washed.

An interesting phenomenon demonstrated by thatching ants, as well as other ants, is the habit of “herding” and maintaining aphid colonies on trees, shrubs and weeds. This occasionally leads to an aphid problem because, while keeping aphids for their sweet honeydew, they protect the aphids against natural control organisms such as wasps and lady beetles. However, they deter other, more serious plant pests, so even in heavy aphid infestations they are still beneficial.


Identification and Life Cycle

Most species of thatching ants are bicoloured red and black. A few are all black. They are medium to large ants, averaging from 4.8mm (three-sixteenths to five-sixteenths of an inch) long, with a notch or depression on the top of the thorax when viewed from the side. They are polymorphic, that is, the workers vary in size within the same colony. Their reproductive swarms (winged males and queens leaving the colony) occur in late summer to early fall.

Thatching ants can be confused with carpenter ants. A sure way to distinguish them from carpenter ants is to view them from the side and determine if the thoracic dorsum is smoothly rounded. All carpenter ants have this rounded thoracic dorsum. Thatching ants have a notch or dip on the thoracic dorsum. This diagnostic tool works only when comparing workers of either species. The workers are wingless, possess elbowed antennae, and have a narrow pedicel (wasp waist) of one or two segments between the thorax and the abdomen.



Be sure these ants are, indeed, a threat if you find them residing on your property because, as mentioned, they are beneficial. If you determine them to be a pest, pyrethrin or cyfluthrin, can be effectively used if applied properly. Do not merely apply to the nest entry hole. The ants will simple create another entry or move their nest to a nearby location. Therefore, the entire nest surface and subterranean portion should be thoroughly treated with the pesticide.

One method is to penetrate the nest by digging deeply and stirring the nest contents with something like a sturdy shovel while pouring the recommended dosage of insecticide into the nest and surrounding area. This is best done by two people. To avoid bites, attach a plastic sleeve (for example, a plastic bag attached with a rubber band) below the point where your hands will be placed on the stirring implement. Since the ants cannot travel on this slippery surface, this prevents them from crawling up the implement and biting you. Boots are also recommended, with plastic or polyethethylene leggings attached around the ankles to prevent ants from going up your pant legs. To make leggings, cut the bottom out of a long plastic bag and fasten it into position from ankle to knee with rubber bands, top and bottom. Even though you use safety measures, you should complete the application quickly. Ants are social insects.


Most ant colonies are started by a single queen. From this single individual, colonies can grow to anywhere from several hundred to several thousand individuals. Ants normally produce reproductive forms once a year. Colony activity at this time is high, with winged males, queens, and workers in a very active state. The queen and males fly from the colony, mate, and shortly thereafter the male dies. The inseminated queen then builds a small nest, lays a few eggs, and nurtures the developing larvae which soon hatch. When the adult workers appear, they take over the function of caring for the queen and larvae, building the nest, and bringing in food for the colony. Colonies of some species may persist for 20 years or more.

*Use pesticides with care. Apply them only to plants, animals, or sites listed on the label. When mixing and applying pesticides, follow all label precautions to protect yourself and others around you. It is a violation of the law to disregard label directions. If pesticides are spilled on skin or clothing, remove clothing and wash skin thoroughly. Store pesticides in their original containers and keep them out of the reach of children, pets, and livestock. The law requires that pesticides be used as the label directs.