Tadpole's Outdoor Blog

August 1, 2013

Crazy ants

Filed under: Misc — Freddie Keel @ 5:56 am

Crazy ants are invading parts of the U.S., including Houston

By Craig Hlavaty | May 16, 2013

According to researchers at The University of Texas at Austin, invasive “crazy ants” are slowly displacing fire ants in the southeastern United States. These “Tawny Crazy Ants” have a peculiar predilection toward electronics as well.

“They nest in electronics and create short circuits, as they create a contact bridge between two points when they get electrocuted they release an alarm pheromone,” says UT research assistant Edward LeBrun.

“The other ants are attracted to the chemicals that other ants give off,” he adds. At this point, more ants arrive and create a larger nest.

These crazy ants do not sting like fire ants. They will bite, but you will not feel it like you would a fire ant sting. Those bites are a hallmark of growing up in Texas.

The tiny invaders have become quite common in the Houston area, first discovered in 2002 by pest control worker Tom Rasberry. He alerted Texas A&M scientists of his discovery.

At one point they were called “Raspberry Crazy Ants” after the pest fighter. The scientific name is Nylanderia fulva, which doesn’t quite have the ring of “crazy ants.”  

 The ants should be contained where you find them and then exterminated. They thrive on human movement.

“You shouldn’t move them around. They nest in anything, boxes, potted plants,” says LeBrun. As the ants travel, they disrupt other ant populations. Their colonies survive, unlike fire ants.

LeBrun adds that there is not much you can do other than call pest control if you have crazy ants.  You need chemicals that are not commonly found at the hardware store.

The ants do not consume most of the poison baits that kill fire ant mounds, and there is no other ant population that keeps their numbers in check.


Tawny (Rasberry) Crazy Ant

Nylanderia fulva

exotic ant

A new exotic invasive pest ant species to Texas was found around Houston (Harris County), in 2002, and has begun to spread largely through human assistance. The ant has recently been identified as Nylanderia fulva (formerly Nylanderia sp. nr. pubens) and the new proposed common name is the tawny crazy ant (formerly Rasberry crazy ant) (Gotzek, et al 2012). Currently, little is known regarding the biology of this ant. The Center for Urban and Structural Entomology at Texas A&M University has investigated numerous management strategies, diet preference, colony growth and immature development, and this species’ ability to translocate pathogenic microorganisms (see Danny McDonald’s dissertation: Investigation of an invasive ant species: Nylanderia fulva colony extraction, management, diet preference, fecundity, and mechanical vector potential and Jason Meyers’ dissertation: “Identification, distribution and control of an invasive pest ant, Paratrechina sp. (Hymenoptera:Formicidae), in Texas”).

What is an “invasive species”? (See the invasive species fact sheet)

Identification: How do I spot them?

Ants under boardPhoto by Danny McDonald

Suspect tawny ants if you see a lot of ants with the following characteristics (see full listing of characteristics below):

  • Appearance of many (millions) of uniformly-sized 1/8 inch long, reddish-brown ants in the landscape; foraging occurs indoors from outdoor nests.
    (Click to see video of these ants found in the grass.)
  • Under a microscope you will find 12-segmented antennae, a petiole (1 node), an acidopore (circle of hairs at the tip of the gaster (abdomen)), and the ant will be covered with many hairs (macrosetae).
  • Winged males (see image below) are needed for identification to species (see Gotzek et al. 2012)
  • Ants that form loose foraging trails as well as forage randomly (non-trailing) and crawl rapidly and erratically (hence the description “crazy” ant).
  • Ant colonies (where queens with brood including whitish larvae and pupae, See image on right) occur under landscape objects like rocks, timbers, piles of debris, etc. These ants do not build centralized nests, beds, or mounds, and do not emerge to the surface from nests through central openings.

A guide entitled, “The Common Ant Genera of Texas” (B-6138) is available at: http://agrilifebookstore.org. This reference will help identify the ants the the genus, Nylanderia, to which this invasive ant belongs. Several other species of Nylanderia occur in the state (see “The Distribution of Ants in Texas” at http://sswe.tamu.edu/PDF/SWE_S22_P001-92.pdf).
The description of the tawny crazy ant is very similar to the species description for Nylanderia pubens, the Caribbean crazy ant.  Currently, there is no approved common name for this ant by neither the Code of Zoological Nomenclature nor the Entomological Society of America (see http://www.entsoc.org/pubs/common_names).
The black crazy ant, Paratrechina longicornis (see http://urbanentomology.tamu.edu/ants/crazy.html), may in some cases create massive, but localized numbers. These species look similar, but have marked differences.  Paratrechina longicornis antennae and legs are significantly longer than that of Nylanderia fulva.  P. longicornis mesosoma (thorax) is extended in length considerably, compared to that of the Nylanderia species.  Although the use of color as an identification tool is not to be relied upon, the crazy ant is often jet black in color, especially when compared to the typically reddish-brown of N. fulva.
Submitting ant samples for identification: If you are a pest control operator and you suspect your client may have these ants, please contact the Center for Urban & Structural Entomology. Please send samples in sealed vials containing alcohol.  Specific location data would be greatly appreciated (address, GIS coordinates).  For more information on submitting samples: See Identification Request Form.

Impact: What do they do?

In infested areas, large numbers of tawny crazy ants have caused great annoyance to residents and businesses. In some situations, it has become uncomfortable for residents to enjoy time in their yards. Companion animals may, in some cases, avoid the outdoors as well, and wildlife such as nesting songbirds, can be affected. The cumulative economic impact is currently unknown.

Biting and medical implications to people, livestock and wildlife: Tawny crazy ants do not have stingers. In place of a stinger, worker ants possess an acidopore on the end of the gaster (abdomen), which can excrete chemicals for defense or attack. They are capable of biting, and when bitten, they cause a minute pain that quickly fades.

Nylanderia fulva, has been a serious pest in rural and urban areas of Colombia, South America. In this case, they reportedly displaced all other ant species and caused small livestock (e.g. chickens) to die of asphyxia. Larger animals, such as cattle, have been attacked around the eyes, nasal fossae and hooves. The ants also caused grasslands to dry out (dessicate) because the ants aggravated sucking insect pests (hemipterans) because the ants feed on the sugary “honeydew” produced by these plant feeding insects.

electric box

Electrical equipment: In areas infested by the tawny crazy ant, large numbers of ants have accumulated in electrical equipment, causing short circuits and clogging switching mechanisms resulting in equipment failure (see “Ants and Their Affinity for Electrical Utilities” at http://www.extension.org/pages/30057/ants-and-their-affinity-for-electrical-utilities).

In some cases the ants have caused several thousand dollars in damage and remedial costs.

Agriculture: Todd Staples, Commissioner of Agriculture, suspects this to be a potentially serious agricultural pest (see Press Release). These ants show likelihood of being transported through movement of almost any infested container or material.  Thus, movement of garbage (see image B below), yard debris (see image A below), bags or loads of compost, potted plants, and bales of hay can transport these ant colonies by truck, railroad, and airplane. No information is available on potential yield effects in infested lands.

Rasberry Crazy Ants in Leaf Bag Rasberry Crazy ant in Trash can
A. Rasberry crazy ants found in bag of leaves
Click to watch video
B. Rasberry crazy ants found in trash can
Click to watch video
To view these videos you need Apple’s QuickTime Video Player

Impact: What affect do they have on wildlife?

Wildlife such as nesting songbirds is irritated by the tawny crazy ants.  Masses of crazy ants covering the ground and trees likely affect ground and tree-nesting birds and other small animals and cause wildlife to move out of the area.

The ants are even displacing red imported fire ants in areas of heavy infestation. However, after experiencing the tawny crazy ant, most residents prefer the fire ant.

Very little is currently known about the wildlife impact from the tawny crazy ants in the United States. If you observe any affect to wildlife, please report it to Texas Parks and Wildlife Department by submitting the “Wildlife Impact Report” form.

Biology: ID Characteristics & Behavior

Worker ant body characteristics:

Exotic AntTawny crazy ant worker
Photo by Danny McDonald
Click on the image to view the major identifying characteristics.

  • Coloration: Adult colony members, including queens, males and workers, are reddish-brown (although lightness or darkness of their body color may vary)
  • Size: Worker ants are all similar in size (they are monomorphic), with a body length of 1/8 inch.
  • Worker ants have long legs and antennae, although not as long as the crazy ant, Paratrechina longicornis, and their bodies have numerous, long, coarse hairs. The antenna have 12-segments with no club.
  • There is a small circle of hairs (acidopore) present at tip of the abdomen (as opposed to the typical stinger found in many ants), a characteristic of formicine ants (found within the Formicinae subfamily).

Exotic AntTawny crazy ant male alate (top) and pupae (bottom)
Photo by Bart Drees


  • Tawny crazy ants can been found in enormous population densities. They are social insects that live in large colonies or groups of colonies that seem to be indistinguishable from one another.
  • Colonies contain many queen ants (they are polygyne colonies), worker ants, and brood consisting of larval and pupal stages.  Pupae are “naked” or without cocoons. They periodically produce winged male and female forms called sexuals, alates, or reproductives.
  • The size of the colony infestations can be large and display super colony (unicolonial) behavior

Trailing behavior:

  • Tawny crazy ants foraging trails are quite apparent (≥10 cm) and individuals forage erratically, hence the typical reference to “crazy” ant. Foraging trails will often follow structural guidelines (See image below), however, large trails can be found in open areas.

Ants under board

Nesting and nesting behavior:

  • Rasberry crazy ant colonies can be found under or within almost any object or void, including stumps, soil, concrete, rocks, potted plants, etc.
  • Nests primarily occur outdoors, but worker ants will forage indoors, into homes and other structures.
  • Nesting occurs under almost any object that retains moisture.

Ants tending aphidsTawny crazy ant tending aphids. Photo by Danny McDonald.

Food and feeding behavior:

  • Tawny crazy ants eat almost anything; they are omnivorous.
  • Worker ants commonly “tend” sucking hemipterous insects such as aphids, scale insects, whiteflies, mealy bugs, and others that excrete a sugary (carbohydrate) liquid called “honeydew” when stimulated by the ants.
  • Workers are attracted to sweet parts of plants including nectaries, damaged, and over-ripe fruit.
  • Worker ants also consume other insects and other small vertebrates for protein.
  • Click here to view a video by Bart Drees titled “Rasberry crazy ant feeding on oak aphid honeydew

Seasonal abundance:

  • Few worker ants forage during cooler winter months.
  • In spring foraging activity begins and colonies grow, producing millions of workers that increase in density dramatically by mid-summer (July-August).
  • Ant numbers remain high through fall (October-November).

Female Rasberry Crazy AntTawny crazy ant female alate
Photo by Johnny Johnson

Male Rasberry Crazy AntTawny crazy ant male alate
Photo by Johnny Johnson

Natural spread:

  • No mating (nuptial) flights have been observed in the field, despite the periodic development of winged male and female ants, called sexuals, alates, or reproductives. This indicates that colonies spread or propagate by “budding” with breeding possibly occurring at/near the edge of the nest, creating new colonies at the periphery. Annual rate of spread by ground migration is ~20 and ~30 m per month in neighborhoods and industrial areas respectively and ~207 m/year in rural landscapes.

Distribution: Where are they found?

Carribean Ant Map

The tawny crazy ant has only been known in the state of Texas (near Pasadena) since 2002. High numbers of the ants have been found in localized spot infestations in southeast Houston (Harris County), including Houston, Pasadena, Deer Park, Friendswood, San Jacinto Port, Pearland, Seabrook and La Porte.

The tawny crazy ant has now been confirmed in 24 counties, including Bexar, Brazoria, Brazos, Comal, Cameron, Fort Bend, Chambers, Galveston, Hardin, Harris, Hidalgo, Jefferson, Jim Hogg, Liberty, Matagorda, Montgomery, Nueces, Polk, Orange, Travis, Victoria, Walker, Wharton and Williamson counties. New infestations are suspected beyond these areas of infestation. However, sample identifications have not been confirmed. This ant has the potential to spread well beyond the current range in coastal Texas. However, it is a semi-tropical ant and potential northern distribution will be limited by cooler weather conditions.

Management: What can you do for them?

Rasberry Crazy ant pile

Many of the typical control tactics for other ants do not provide adequate control of the tawny crazy ant. Because colonies predominantly nest outdoors, reliance on indoor treatments (see Rasberry Crazy Ant Fact Sheet or YouTube Video) to control these ants foraging inside structures is not effective.

Cultural control: At the foundation of any IPM strategy are cultural control methods beginning with the removal of harborage such as fallen limbs, rocks, leaf litter, and just about anything sitting on the ground that isn’t absolutely necessary.  Cultural methods can also include altering the moisture conditions in a landscape.  Crazy ants prefer humid, wet conditions so reducing the amount of irrigation, repairing leaks, and improving drainage should help.

Rasberry Crazy ant barrier treatment

Avoid spreading this species to new locations: Anything being moved from an infested area should be inspected for ants and treated before transferring it to a new site.  Food sources should be eliminated or managed.  Specifically honeydew producing hemipterans should be managed.  Often, products containing the active ingredient imidaloprid or other systemic neonicotinoid are a good option for hempiterans.

Chemical control: Effective products involved with the treatments are not readily available to the consumer**. If you suspect your house or property is infested with these ants, call a professional pest control provider. After treatment, or when making multiple applications over time, piles of dead ants must be swept or moved out of the area in order to treat the surface(s) underneath.

Tawny crazy ant workers are not attracted to most bait products (see B-6099, “Broadcast Baits for Fire Ant Control“) and the most attractive product they are attracted to (Whitmire Advance Carpenter Ant Bait formulation containing abamectin (Label and MSDS), see E-412 “Carpenter Ants“) does not offer enough control as a standalone treatment, and should be used in conjunction with contact insecticides.  Maxforce® Granular Insect Bait is also highly attractive but has yet to be tested in the field.

There are treatments available for this ant that offer temporary “buffer zones” using contact insecticides applied to surfaces, such as those containing acephate, pyrethroid insecticides (bifenthrin, cypermethrin, cyfluthrin, deltamethrin, lambda-cyhalothin, permethrin, s-fenvalerate, and others) or fipronil. These treatments are often breeched within 2-3 months post application.

PCOs need access to an entire infestation in order to achieve an acceptable level of management. Otherwise, the population will rebound from surrounding, untreated sites within a month.

**Note for Professional Pest Management Personnel: According to the Texas Department of Agriculture, the following products have received expanded use approval through a Section 18 Quarantine Exemption from the Texas Department of Agriculture (TDA) and the Environmental Protection Agency (EPA) for the control of these ants. These are only available for use in counties with confirmed infestations of the tawny crazy ant. See product labels and supplemental labels for specific use directions: This exemption will expire on November 1, 2015.

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