Tawny Crazy Ant | Nylanderia fulva

California Pest Rating  for
Tawny Crazy Ant | Nylanderia fulva
Hymenoptera:  Formicidae
Pest Rating: A  



Initiating Event:

Several Nylanderia species have been intercepted 31 times in 2017 by CDFA through various regulatory pathways. Nylanderia fulva, the tawny crazy ant is an invasive species that has invaded the southern states of Texas, Louisiana, Mississippi, Alabama, Florida and Georgia (Wang et. al, 2016). Nylanderia species have been rated as Q.  A pest rating proposal is needed to assign a permanent rating.

History & Status:

Background:  Ants in the genus Nylanderia are relatively small, pale yellow to black. Nylanderia fulva in the U.S. were originally identified as Paratrechina sp. cf. pubens and later revised to N. fulva. The true N. pubens is also an invasive pest, but is apparently restricted to southern Florida. Worker ants of these two species cannot be distinguished morphologically, so clear identification requires examination of male specimens.

 Nylanderia fulva is also known as the crazy ant due to its quick and erratic movement. It is a small, reddish brown ant that forms huge colonies, and is a serious nuisance pest. (MacGown and Layton, 2010). Nylanderia fulva infests buildings and greenhouses. This ant can attack domestic animals, honeybee hives, and several crop plants; it can also displace native ant species (Hill et.al, 2013). It can aggregate in large numbers in electrical equipment and cause short circuits or clog switching mechanisms, resulting in equipment failure.

The Tawny crazy ant is a social insect usually found in large numbers that lives in large colonies and seem to be indistinguishable from each other. Males and workers are similar in size while queens are larger. Colonies contain many queens, workers and brood (larvae and pupae). Pupae are naked (without cocoons). Colonies periodically produce winged male and female forms called sexuals, alates or reproductives. Foraging activity begins in spring and worker populations increase dramatically in density by mid- summer. (Nestor, 2002)

Worldwide Distribution:

Nylanderia fulva is native to South America, specifically southern Brazil and northern Argentina along the border of Uruguay and Paraguay (Kumar et. al., 2015). It has established in Anguilla, Bermuda, Colombia, Cuba, Guadeloupe, Martinique, Panama, Puerto Rico and the U.S. Virgin Islands. (Hill et. al., 2013)

In the United States, it was first recognized as N. fulva near Houston, Texas in 2002, but this record is preceded by previous misidentifications as N. pubens in Florida. Currently, Nylanderia fulva has become established in the states of Texas, Louisiana, Mississippi, Alabama, Florida, and Georgia.

Official Control: Nylanderia fulva has not been listed as a harmful organism in any U.S. states or other nations (PCIT, 2018).

California DistributionNylanderia fulva has never been found in the natural environment of California.

California InterceptionsNylanderia species were intercepted 107 times between July 2013 and January 2018 by CDFA through detection surveys, border stations, dog team inspections, and high-risk pest exclusion activities.

The risk Nylanderia fulva (tawny crazy ant) would pose to California is evaluated below.

Consequences of Introduction: 

1) Climate/Host Interaction: Nylanderia fulva is omnivorous and its foraging trails widens  as the temperature rises to 20°C. Foraging activity begins in spring and worker density can increase to millions during July – August and the number of ants remain high throughout fall. Nests can occur in leaf litter, soil, rotten logs, under potted plants, under rocks and along underground electrical circuits (Sharma et al., 2014). California’s climate and habitat would be suitable for occurrence of nests and rapid increase in          populations. It receives a High (3) in this category.

Evaluate if the pest would have suitable hosts and climate to establish in California:

Score: 3

– Low (1) Not likely to establish in California; or likely to establish in very limited areas.

– Medium (2) may be able to establish in a larger but limited part of California.

High (3) likely to establish a widespread distribution in California.

2) Known Pest Host Range: Nylanderia fulva worker ants tend plant-feeding hemipterous insects such as aphids, scale insects, whiteflies, mealy bugs and others that excrete honeydew. Workers are also attracted to sweet parts of plants including nectaries, and damaged and over-ripe fruit. They also consume other insects and small vertebrates for protein (Nestor, 2002). These hosts can be found throughout California. It receives a Medium (2) in this category.

Evaluate the host range of the pest:

Score: 2

– Low (1) has a very limited host range.

Medium (2) has a moderate host range.

– High (3) has a wide host range.

3) Pest Dispersal Potential: Nylanderia fulva queens lay single, white, ovoid-shaped eggs that incubate for approximately 16 days. The larvae that emerge pass through three (workers) or four (males) instars and the larval stage lasts about 11 days. Workers carry pupae to the nest where they are piled into mounds. Adults emerge from pupae after 12 days. Nuptial flight activity has not been recorded until recently. New findings have confirmed that alate males fly throughout the year but females are produced only once a year (Wang, et al., 2016). Colonies spread by budding with breeding occurring at the periphery. The annual rate of spread by ground migration is about 20-30 m per month in industrial areas and about 207 m per year in rural landscapes (Nestor, 2002). Nylanderia fulva can be transported long distances by the movement of infested material including garbage, yard debris, compost, potted plants and bales of hay transported by truck, railroad and airplane. It receives a High (3) in this category.

Evaluate the natural and artificial dispersal potential of the pest:

Score: 3

– Low (1) does not have high reproductive or dispersal potential.

– Medium (2) has either high reproductive or dispersal potential.

High (3) has both high reproduction and dispersal potential.

4) Economic Impact: Nylanderia fulva, in large numbers, can become a nuisance and make human activities uncomfortable and difficult. Infestations can extend to sidewalks, buildings and gardens. These ants are capable of biting small livestock, causing them to die of asphyxia and can attack large animals around their eyes, nasal fossae and hooves. Their foraging and nesting behavior can cause short circuits in electrical equipment. Since this species feeds on the exudate of hemipteran insects, it can result in the disruption of biocontrol and cause losses from increased crop damage. This species has been reported to destroy honey bee hives in Texas by consuming brood, and then colonizing the hive (Harmon, 2009). It receives a High (3) in this category.

Evaluate the economic impact of the pest to California using the criteria below:

Economic Impact: A, B, D, F

A. The pest could lower crop yield.

B. The pest could lower crop value (includes increasing crop production costs).

C. The pest could trigger the loss of markets (includes quarantines).

D. The pest could negatively change normal cultural practices.

E. The pest can vector, or is vectored, by another pestiferous organism.

F. The organism is injurious or poisonous to agriculturally important animals.

G. The organism can interfere with the delivery or supply of water for agricultural uses.

Economic Impact Score: 3

– Low (1) causes 0 or 1 of these impacts.

– Medium (2) causes 2 of these impacts.

– High (3) causes 3 or more of these impacts.

5) Environmental Impact: Nylanderia fulva is likely to reduce biodiversity of other animals, both invertebrates and vertebrates. Larger ant populations have forced ground and tree nesting birds and other small animals to move out of the area (LeBrun et. al, 2013). Masses of these ants covering the ground and trees can cause wildlife to move out of the area. Ecological impacts by fulva include reduction in arthropod diversity, particularly native ant species. This ant can undoubtedly impact ecosystems in its adventive range and has the potential to cause cascading ecological impacts (Wang et al., 2016). Large infestations may be difficult to control and would need professional pest control services to treat affected areas. It receives a High (3) in this category.

Evaluate the environmental impact of the pest on California using the criteria below:

Environmental Impact: A, B

A. The pest could have a significant environmental impact such as lowering biodiversity, disrupting natural communities, or changing ecosystem processes.

B. The pest could directly affect threatened or endangered species.

C. The pest could impact threatened or endangered species by disrupting critical habitats.

D. The pest could trigger additional official or private treatment programs.

E. The pest significantly impacts cultural practices, home/urban gardening or ornamental plantings.

Score the pest for Environmental Impact:

Environmental Impact Score: 3

– Low (1) causes none of the above to occur.

– Medium (2) causes one of the above to occur.

High (3) causes two or more of the above to occur.

Consequences of Introduction to California for Nylanderia fulva (tawny crazy ant): High (14)

Add up the total score and include it here:

-Low = 5-8 points

-Medium = 9-12 points

High = 13-15 points

6) Post Entry Distribution and Survey Information: Nylanderia fulva (tawny crazy ant) has never been found in the environment in California and receives a Not established (0) in this category.

Evaluate the known distribution in California. Only official records identified by a taxonomic expert and supported by voucher specimens deposited in natural history collections should be considered. Pest incursions that have been eradicated, are under eradication, or have been delimited with no further detections should not be included:

Score: 0

Not established (0) Pest never detected in California, or known only from incursions.

-Low (-1) Pest has a localized distribution in California, or is established in one suitable climate/host area (region).

-Medium (-2) Pest is widespread in California but not fully established in the endangered area, or pest established in two contiguous suitable climate/host areas.

-High (-3) Pest has fully established in the endangered area, or pest is reported in more than two contiguous or non-contiguous suitable climate/host areas.

Final Score:

The final score is the consequences of introduction score minus the post entry distribution and survey information score: High (14)


Five species of Nylanderia are native to the southwestern United States including California. Nylanderia fulva has a potential to overlap with these native species. Since this species is currently established in the southeastern states mentioned above, any host material coming from those areas could potentially contain N. fulva. The presence of only a few workers in incoming samples can also make it difficult to identify Nylanderia to species level because males are needed to positively identify N. fulva.  Detection surveys in California would likely aid in the early detection of this invasive ant.

Conclusion and Rating Justification:

Nylanderia fulva has not been recorded in the environment of California and would likely have significant economic and environmental impacts if it were to enter the state.  An “A”-rating is justified.


Harmon, K. 2009. Honeybees Face New Threat in Texas: “Crazy” ants. Accessed 1/25/18.  (http://www.scientificamerican.com/blog/post.cfm?id=honeybees-face-new-threat-in-texas-2009-08-07).

Hill, S.K., Baldwin, R.W., Pereira, R.M. &  Koehler, P.G., 2013. Tawny Crazy Ant. Publication # SP486D, University of Florida, Accessed 1/26/18 http://edis.ifas.ufl.edu/pdffiles/IN/IN107600.pdf.

Kumar, S., LeBrun, E.G., Stohlgren, T.J., Stabach, J.A.,McDonald, D.L., Oi, D.H. &  J.S. LaPolla. 2015. Evidence of niche shift and global invasion potential of the tawny crazy ant, Nylanderia fulva. Ecol. 5, 4628–4641

LeBrun, E. G., Abbott. & L. E. Gilbert. 2013. Imported crazy ant displaces imported fire ant, reduces and homogenizes grassland ant and arthropod assemblages. Biological Invasions 15: 2429-2442.

MacGown, J. A. & B. Layton. 2010. The invasive Rasberry crazy ant, Nylanderia sp. near pubens (Hymenoptera:  Formicidae), Midsouth Entomologist Vol 3: 1:  441- 47. Accessed1/26/18. http://midsouthentomologist.org.msstate.edu/Volume3/Vol3_1_html_files/vol3_1_008.htm

Nestor, P.R. 2002. Tawny (Rasberry) Crazy Ant. Center for Urban and Structural Entomology. Texas A & M Agrilife Extension. Accessed 1/25/18.  http://bugwoodcloud.org/resource/files/6305.pdf

Pest and Damage Record Database. Pest Prevention and Plant Health Services. CA Department of Food and Agriculture. Accessed 1/24/18. http://phpps.cdfa.ca.gov/user/frmLogon2.asp

Sharma, S, Warner, J and R.H. Scheffrahn, 2014. Featured Creatures. Tawny Crazy Ant. Nylanderia fulva. Entomology and Nematology Department, University of Florida. Accessed 1/25/18.  http://entnemdept.ufl.edu/creatures/urban/ants/tawny_crazy_ant.htm

USDA Phytosanitary Certificate Issuance & Tracking System (PCIT) Phytosanitary Export Database (PExD). Accessed 1/24/18. https://pcit.aphis.usda.gov/PExD/faces/PExDReport.jsp

Wang, Z., Moshman, L., Kraus, E.C., Wilson, B.E. Acharya N., and Diaz, R., 2016. A Review of the Tawny Crazy Ant, Nylanderia fulva, an Emergent Ant Invader in the Southern United States: Is Biological Control a Feasible Management Option? Department of Entomology, Louisiana State University Agricultural Center, Baton Rouge, LA 70803, USA; Accessed 1/24/18. www.mdpi.com/2075-4450/7/4/77/pdf


Raj Randhawa, 1220 ‘N’ Street, Room 221, Sacramento CA 95814, (916) 403-6617, plant.health[@]cdfa.ca.gov

Responsible Party:

Jason Leathers, 2800 Gateway Oaks, Sacramento CA 95833, (916) 654-1211, plant.health[@]cdfa.ca.gov

Comment Period:* CLOSED

4/12/18 – 5/27/18


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Pest Rating: A  


Posted by ls