Swarming Insects Indoors

This ant swarmer is identified by its pinched waist and bumpy stem connecting the thorax and tail (gaster).

This ant swarmer is identified by its pinched waist and bumpy stem connecting the thorax and tail (gaster).

When large numbers of winged insects suddenly appear in the home, it may be the result of an insect mating swarm. When insects produce a swarm, also known as a reproductive flight, it is part of the seasonal activity of certain social insects, most importantly termites and ants. Normally insect swarms occur outdoors on a still, warm day. But if an ant or termite nest is close enough to a home, swarms may occur indoors.

What are swarmers?

Ants and termites are social insects with highly developed social organizations. Social insect societies are organized according to various castes, groups of physically distinct individuals with unique functions. The worker caste usually makes up the largest part of a social insect colony. Worker ants are those ants we see most often feeding at our tables and foraging outdoors for food for the colony. Worker termites are the small white insects we see when we break open a piece of decaying wood. All workers are female in the social insect world.

Another important caste for social insects is the reproductive caste. The reproductive caste consists of both males and females. At certain seasons of the year ant and termite colonies produce many such reproductives. These include the “kings” and “queens” of future colonies. Unmated insects are called pre-reproductives and usually possess wings prior to leaving the colony. Pre-reproductives remain inside the nest for varying periods of times–sometimes for several months–waiting for the proper signals to leave the nest in search of new mates. When they emerge from the nest in large numbers they are said to swarm. The pre-reproductives are called swarmers at this time.

Why do insects swarm?

Why the bother? Why do insects leave their colony to mate? It seems like it would be easier and safer to partner with fellow nest mates and avoid the danger of leaving a secure nest.  The answer seems to be that nature programs termites and ants with this behavior to  to ensure better genetic mixing between colonies. Genetic mixing helps a species remain strong and better able to adapt to changing environmental conditions.

An interesting thing about swarming is that it typically occurs simultaneously among colonies in the same area.  With no direct communication between different colonies, ants and termites seem to know when other colonies of the same species are going to send out potential mates, and time their swarms accordingly.  Swarming is often triggered by one or more environmental clues such as temperature, wind speed, relative humidity and day length. Fire ants, for example, send out swarmers in the spring when the relative humidity is high and the wind speed is low. By using identical environmental cues to trigger swarming, ants and termite colonies increase the chance that their reproductives will encounter swarmers from other colonies of the same species.

Should I be concerned?

When you find numerous swarming ants inside your home, it means there is an ant nest either inside, underneath or very close to the structure. In most cases, if worker ants have not previously been a problem inside the home, the presence of swarming ants indoors should not be a cause for concern. Swarming typically lasts for only one or just a few days. This, and the fact that reproductive flights only occur once to a few times a year, means that a vacuum cleaner, or one-time use of an indoor flying insect spray, is often all that is needed to solve the problem.

If you see no other evidence of ants other than occasional swarmers, then no further control may be needed.  On the other hand, swarming ants may be evidence of an undesirable infestation. Pharaoh ants and carpenter ants are two species that can become chronic pests in a home or other structure. If a home has an infestation of either of these species, chances are that worker ants will be continuously present indoors, and may require treatment.

Swarming fire ants indoors usually indicate an outdoor nest adjacent to the building foundation. If fire ants swarm indoors, locate and treat the outdoor mound with a low-odor insecticide. Failure to treat fire ants that are nesting close to your house may result in mass invasions of fire ant workers, especially during the hot summer months.

Having termites swarm in your home is an almost sure indication of a termite infestation. Unless it’s apparent that the termite entered through an outdoor window, you should contact a termite control professional. Save any specimens you discover for a professional to examine. The best way to preserve a specimen is to place it in a crush-proof container in alcohol (rubbing alcohol is fine). Make a note of the date and which room it was collected from. This information will help a pest control professional inspect your home more efficiently. Many suspected termite infestations turn out, on close inspection, to be some other insect. If you find your home infested it is best to work with a professional termite or pest control company to eliminate the problem.

Distinguishing ants and termites

Fortunately termite and ant swarmers are relatively easy to identify.

Ant swarmers are distinguished from termites by their pinched waists and elbowed antennae. Swarmers may or may not have wings.

Ant swarmers are distinguished from termites by their pinched waists and elbowed antennae. Swarmers may or may not have wings.

Termites are recognized by their dark, straight sided bodies and long, equal-length wings. Ant swarmers have distinctly pinched waists (the joint between thorax and abdomen) and the four wings are unequal in length (two long and two relatively short). Ant antennae also bend sharply in the middle, whereas termite antennae are flexible throughout their length. Both ants and termites are relatively small, from 3/16 inch for the smaller ants and termites to 3/8 inch for the larger ants. Ant swarmers are usually larger than the worker ants from the same colony.

Both ants and termites can lose their wings shortly after emergence, so it is common to find reproductive ants and termites without wings.

For more information

For more information about termites and their control, see Extension publication E-368. For more information about fire ants, see Extension Leaflet L-5070. For more information about other indoor ants, see Extension Leaflet B-6183.


Michael Merchant, Ph.D., Professor and Extension Urban Entomologist, Texas AgriLife Extension Service. Dallas, TX.

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