What Are Crazy Ants?

Stephanie L. Richards, PhD, Medical Entomologist

Where are crazy ants found?

Nylanderia fulva, also known as the tawny crazy ant, is native to South America (primarily Argentina and southern Brazil), but has invaded the southern region of the United States. The tawny crazy ant, one of several crazy ant species, was first detected in Texas in 2002 and has since spread to Alabama, Florida, Georgia, Louisiana and Mississippi.

The biology of crazy ants is similar to other ant species. Queen ants (up to five queens per nest) lay eggs that hatch into larvae. The larvae go through three to four developmental stages, called instars, before completing metamorphosis into pupae and then adults. Crazy ant nests are found in well-drained soil and may be up to 1 square meter in size. These ants, unlike many other species, do not make nests that look like mounds of soil.

Although winged ants have been found, no flights have been observed. Hence, at this point, scientists believe the crazy ants are invading geographically dispersed areas primarily due to human transport.

This invasive species is an omnivore, hence it feeds on a variety of substrates. Crazy ants commonly obtain honeydew secretions from other insects, such as aphids. They can also be found feeding on flower nectar and ripened fruit. Worker ants of crazy ant colonies may kill and eat other arthropods (e.g., spiders) and even small vertebrate animals (e.g., snakes, birds). Crazy ants will feed on additional protein sources, such as discarded human food, hence routine trash cleanup is necessary.

Although the crazy ant is still expanding its range, scientists hypothesize that the crazy ant will not become distributed as far north as the red imported fire ant (Solenopsis invicta). The crazy ant is considered a semi-tropical species and is primarily active in spring, summer and fall months.

Why are they called crazy ants?

Crazy ants get their name from the unpredictable way in which they move. They usually do not follow pheromone trails like other ants.

What is unique about the behavior of crazy ants?

Crazy ants show a high level of aggression towards other species of ants. Scientists believe that crazy ants may be displacing fire ants in some areas due to competition for resources and aggressive behavior. Scientific research has shown that the crazy ants produce a chemical (formic acid) that acts as an antidote to venom from fire ant stings (an alkaloid substance called Solenopsis A). The venom from fire ants is usually fatal to most other ant species, but crazy ants appear immune to its effects. After an encounter with fire ant venom, crazy ant workers have been observed curling their abdomens toward their mandibles, followed by grooming behavior to spread the abdomen secretion (formic acid) over the body (LeBrun et al. 2014). The formic acid of crazy ants changes the chemical composition of the venom from the fire ants, hence rendering it innocuous.

Crazy ants do not have a stinger; however, they can excrete (spray) formic acid from their venom gland as a defense against enemies. The venom is sprayed through an opening called the acidopore.

Should I be concerned about crazy ants?

Crazy ants are considered pests in residential (urban, suburban, rural) and agricultural settings. Some people have reported damage to apiaries (places where beehives are maintained) where crazy ants have killed honey bee larvae. Due to the large foraging range, crazy ants have been found infesting entire subdivisions or golf courses in some locations.

Ant colonies can be detected under a variety of objects that contain humidity/moisture, such as soil, plantings, pavement, rocks, etc. In some cases, large ant infestations can chew electrical wires, causing damage to equipment.

How are crazy ants controlled?

An integrated pest management approach should be used to control infestations of crazy ants. Homeowners should remove any debris (e.g., fallen leaves/branches) that may be providing harborage for ants. It is also important to reduce the amount of moisture in the environment by ensuring irrigation systems are functioning properly and not overwatering vegetation, hence reducing the suitability of soil for ant colonies. Controlling insects that produce honeydew can also help suppress crazy ants by limiting this food source.

Pest management professionals can be consulted where chemical control methods may be needed. In some cases, it may not be possible to completely eliminate populations of crazy ants; however, reduction of populations is possible with surveillance-based targeted control.

Reference

LeBrun EG, Jones NT, Gilbert LE (2014) Chemical warfare among invaders: A detoxification interaction facilitates ant invasion. Science 343:1014-1017.