Nylanderia fulva

(Mayr, 1862)

Tawny Crazy Ant, Rasberry Crazy Ant, Caribbean Crazy Ant, Brown Crazy Ant, Invasive Crazy Ant, Hairy Crazy Ant

Nylanderia fulva, commonly known as the tawny crazy , is an ant to South America that has become a significant pest in the southern United States. The species is characterized by its erratic, rapid movement patterns and ability to form enormous supercolonies with millions of . It was first reported in the continental United States in 1938 but only recognized as a serious pest in the 1990s in Florida and 2000s in Texas. The ant exhibits a unicolonial social structure in its invasive range, with interconnected nests showing no intraspecific aggression.

Nylanderia fulva by (c) Sam Kieschnick, some rights reserved (CC BY), uploaded by Sam Kieschnick. Used under a CC-BY license.

Tawny crazy ant (Nylanderia fulva) male reproductive by Bentleypkt. Used under a CC BY-SA 4.0 license.

Pronunciation

How to pronounce Nylanderia fulva: /nɪˈlændɛriə ˈfʊlvə/

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Identification

Distinguished from the longhorn crazy (Paratrechina longicornis) by its uniform tawny coloration and shorter relative to body length. Separated from Nylanderia pubens, its closely related sister , by molecular characters and subtle morphological differences. The species' erratic movement pattern and dense body help distinguish it from other small ants. In the field, massive colony size and lack of intraspecific aggression are diagnostic of established . The species does not , unlike fire ants (), which it often displaces.

Images

Appearance

are small, approximately 2-3 mm in length (about 1/8 inch), with a uniform tawny to reddish- coloration. The body is covered with dense, pale (hairs), giving a slightly fuzzy appearance. have 12 with no . The lacks a and has reduced cuticular hydrocarbon production compared to other of similar size. When agitated, workers produce formic acid as a defensive secretion.

Habitat

In its range, occupies diverse in South America including tropical and subtropical regions. In the range, thrives in both rural and urban environments. Constructs nests in shallow littoral debris, leaf litter, soil cavities, and man-made structures. In North Florida, observed tunneling below ground during winter, a previously undescribed for this . Shows reduced desiccation due to low cuticular hydrocarbon production, limiting distribution in arid environments.

Distribution

to South America, with confirmed records from Argentina, Colombia, and Peru; exact native limits remain poorly understood. in the United States: first reported 1938, established in Texas, Louisiana, Mississippi, Alabama, Florida, Georgia, and expanding. Also invasive in continental Ecuador and rural/urban areas of Colombia. Modeled potential distribution suggests high invasion risk in tropical coastal and Amazonian regions with bioclimatic similarity to native range.

Seasonality

In North Florida, reach peak from early summer to mid-fall. Colonies likely contract and become localized around permanent nests during seasonal cold months. Year-round activity in warmer parts of range; subterranean tunneling observed during winter cold periods in northern Florida.

Diet

. Liquid diet consists primarily of from sap-sucking ; associated with 28 of across 7 in range, obtaining honeydew while protecting and transporting these . Solid diet includes animal from on live , dead , housefly , other insects, , and higher animals. Uses immatures of soil-inhabiting as protein food for .

Host Associations

Wolbachia (supergroup A strains) - endosymbiont73% rate in Argentine nests; three independent horizontally transmitted infections identified
Homoptera (28 species across 7 families) - producers protected, transported, and installed on plants by
Atta spp. (leafcutting ants) - competition/displacementdisplaced by N. fulva in invaded areas
Solenopsis invicta (red imported fire ant) - competition/displacementdisplaced in range; N. fulva detoxifies fire using cuticular secretions
Solenopsis geminata - competition/displacementdisplaced in and ranges
Azteca spp. - competition/displacementdisplaced in invaded areas
Camponotus senex - reliable index of N. fulva absence in coffee plantations
Myrmecomorba nylanderiae - potential under investigation as agent
Pseudacteon spp. - potential under investigation as agents

Life Cycle

Colonies are polygynous and , containing up to hundreds of reproductive and thousands to millions of . Social organization is multicolonial in range and supercolonial in range, with interconnected nests exchanging unrelated individuals without aggression. occurs in both native and invasive ; not parthenogenetic. Queens and male present in colonies. present year-round in active colonies.

Behavior

Exhibits rapid, erratic, unpredictable movement when disturbed—hence

Ecological Role

pest that dramatically reduces diversity in invaded areas, particularly . Displaces both native and other invasive ants including the . Functions as a significant engineer through massive colony construction and modification of soil and litter . Acts as a keystone mutualist with -producing , altering - interactions. High can disrupt networks and . Potential to facilitate plant transmission through Hemiptera associations.

Human Relevance

Significant economic and nuisance pest. Swarms into electrical equipment causing short-circuits and thousands of dollars in damage to infrastructure, appliances, and electronics. render yards uninhabitable due to overwhelming numbers. Agricultural pest in and other . Displaces fire , leading to ironic nostalgia for previous . Difficult to control with conventional ; current management relies on chemical control with limited success. agents under investigation include Pseudacteon , Myrmecomorba nylanderiae , and a novel polynucleotide virus.

Similar Taxa

Paratrechina longicornis (longhorn crazy ant)Shares erratic movement pattern but distinguished by longer , darker coloration, and different body proportions
Nylanderia pubensSister with similar appearance; separated by molecular and subtle morphological characters; taxonomic identity only recently clarified
Solenopsis invicta (red imported fire ant)Often displaced by N. fulva; distinguished by presence, different coloration, and mound-building

More Details

Chemical Defense

When agitated, produce formic acid as a defensive secretion. Researchers aspirating large numbers report sour taste and burning sensation in throat, requiring collection of smaller groups to reduce agitation.

Supercolony Genetics

Despite acting as a supercolony across wide geographic with no intraspecific aggression, high-resolution SNP analysis reveals genetic substructure among US , with differentiation between Texas, Louisiana, Alabama, Mississippi, Georgia, and Florida. Port city populations most closely related to Buenos Aires, Argentina, suggesting multiple introduction .

Sexually Antagonistic Selection

Genomic region under sexually antagonistic selection identified, with distinct differentially selected in males versus females. Males carry only subset of alleles present in ; females reliably with one allele from male gene pool and different maternal allele.

Thermoregulatory Behavior

Unlike , which tunnels more at cooler temperatures, N. fulva shows highest tunneling performance at warmer temperatures (20°C) but retains capacity to tunnel at 15°C, confirming cold avoidance through subterranean tunneling.

Cuticular Hydrocarbon Reduction

Exhibits greatly reduced cuticular hydrocarbon production compared to other of similar body size, explaining both reduced desiccation and impaired nestmate recognition that facilitates supercolony formation.