Brachymyrmex patagonicus

Brachymyrmex patagonicus - "Dark Rover Ant"

Brachymyrmex patagonicus is a tiny ant species native to South America that has become a significant invasive pest in the southeastern United States, southern Spain, Hong Kong, and Japan. Workers measure approximately 0.8mm in total length with a uniformly dark brown to reddish-brown coloration, and they have a distinctive humped appearance when viewed from the side due to their swollen abdomen covering the single petiole node. They have only nine antennal segments (most ants have twelve) and lack an antennal club. This species is known for its remarkable adaptability, nesting in everything from natural habitats like pine forests and beach areas to disturbed urban environments including landscaping mulch, building walls, and electrical outlets. Colonies are monogyne (single queen) and can contain many hundreds to a few thousand workers, with multiple colonies often existing within just a few centimeters of each other. They feed primarily on honeydew from aphids and other sap-sucking insects but readily accept sweet baits and show seasonal diet shifts, preferring carbohydrates in winter and spring and protein in summer and fall. Unlike many ants, they do not bite or sting, but their small size allows them to invade buildings through tiny gaps, and they have been shown to vector bacteria like E. coli, making them a concern in hospitals and healthcare facilities ^[1][2][3].

Quick Summary

• Difficulty: Expert
• Origin & Habitat: Native to South America (Argentina, Brazil, Chile, Colombia, Paraguay, Uruguay and neighboring countries). Introduced to the southeastern United States (Florida, Georgia, Alabama, Mississippi, Louisiana, Arkansas, Texas, Arizona, California, Nevada, North Carolina, South Carolina, Tennessee), southern Spain, Hong Kong, and Japan. Found in a wide range of habitats from natural pine forests, beaches, and mixed forests to highly disturbed urban areas including landscaping mulch, building structures, and roadside habitats ^[1][4][5].
• Colony Type: Monogyne, colonies are headed by a single queen. Multiple colonies can exist in close proximity (within centimeters) and show considerable mutual tolerance. In the US, colonies are typically small with several hundred to a few thousand workers, and as many as 24 colonies can coexist at a single structure ^[6][3].
• Size & Growth:
  • Queen: ~1.96mm total length ^[7]
  • Worker: ~0.8mm total length ^[7]
  • Colony: Up to a few thousand workers per colony ^[2][3]
  • Growth: Moderate
  • Development: Approximately 100 days at optimal temperature (30°C) ^[8] (Development is temperature-dependent: at 25°C, colonies fail to produce adults, at 30°C, eggs develop to adults in approximately 100 days, at 35°C, development is faster but survival is lower. First eggs appear around 71-94 days after colony founding at 30°C.)
• Antkeeping:
  • Temperature: Keep at 28-30°C for optimal reproduction and development. This species thrives in warm conditions, 30°C is the optimal temperature for reproduction. They can tolerate 25-35°C but development stalls below 30°C and fails entirely at 25°C ^[8].
  • Humidity: Moderate to high humidity preferred. In nature, they nest in soil, rotting wood, and moist areas. Keep the nest substrate consistently damp but not waterlogged. They are often associated with moisture in buildings, commonly found in bathrooms and areas near plumbing ^[1][3].
  • Diapause: No diapause required. As a tropical/subtropical species, they remain active year-round in heated indoor environments. In their introduced range, they do not enter true hibernation but may reduce activity during cooler winter months [AntWiki].
  • Nesting: Highly adaptable. In captivity, they do well in test tubes with moist substrate or Y-tong nests. Their tiny size means chambers and passages should be appropriately scaled. They prefer dark, humid nesting sites and will readily nest in small cavities. Avoid excessive ventilation which can dry out the nest.
• Behavior: Generally calm and non-aggressive. Workers are active foragers, primarily during the day, and use pheromone trails to recruit nestmates to food sources. They readily accept sweet baits and will form foraging trails. They do not bite or sting. Their tiny size makes them excellent escape artists, they can squeeze through tiny gaps that larger ants cannot. Colonies show strong nest-mate recognition and maintain strict colony boundaries. Workers require contact with queen and brood to initiate foraging behavior, workers-only colonies do not forage ^[8][6].
• Common Issues: tiny size means escapes are likely without fine mesh barriers and careful sealing of enclosure edges, colonies are small but numerous, making complete eradication difficult if they establish in your home, they can vector bacteria (E. coli), practice good hygiene and avoid handling them near food preparation areas, seasonal diet changes mean protein is more important in summer/fall while sweets dominate in winter/spring, overheating above 35°C causes colony failure, keep temperatures stable and avoid exceeding this threshold, WARNING: This species is invasive in the southeastern United States, Spain, Hong Kong, and Japan. It is NOT recommended to keep this species outside its native range. If kept, extreme precautions must be taken to prevent any escape, as established invasive populations can cause severe ecological damage.

Housing and Nest Setup

Brachymyrmex patagonicus is a tiny ant that can be kept in standard ant housing. Test tubes work well for founding colonies, use a small test tube with a cotton ball creating a water reservoir. The tube should be small enough that the queen can easily walk across it. For established colonies, Y-tong nests or other formicaria work well, but ensure the chambers are appropriately scaled for their small size. They prefer dark, humid environments, so cover the nest with an opaque cover and keep the substrate moist. Because of their tiny size, escape prevention is critical, use fluon on edges and ensure any connections between outworld and nest are tight. They do not require large spaces, colonies naturally fit into small sheltered areas in the wild ^[1][3].

Feeding and Diet

In the wild, B. patagonicus feeds primarily on honeydew from aphids, scales, and other sap-sucking insects. They readily accept sweet baits like honey, sugar water, and syrups. They also need protein, in laboratory tests, they showed strong preference for tuna and other protein sources, especially in summer and fall. They demonstrate seasonal diet switching: carbohydrates dominate in winter and spring while protein is preferred in summer and fall. For captive colonies, offer a mix of sugar water or honey constantly, and provide protein sources like small pieces of mealworms, crickets, or tuna 2-3 times per week. They are not aggressive foragers and may take time to discover new food sources, place food near foraging areas and be patient ^[1][8][3].

Temperature and Seasonal Care

This species requires warm conditions. The optimal temperature for reproduction is 30°C, at this temperature, queens lay eggs within 71-94 days and workers emerge in about 100 days total. At 25°C, colonies fail to produce adults and queens typically die within 29-83 days. At 35°C, development is faster but survival is lower and no adults emerge. Keep your colony at 28-30°C for best results. A small heating cable on one side of the nest can create a temperature gradient. They do not require diapause or hibernation, as a tropical species, they remain active year-round in heated environments. However, activity may decrease in cooler winter months ^[8].

Behavior and Colony Dynamics

B. patagonicus colonies are monogyne (single queen) and maintain strong nest-mate recognition. Colonies can coexist in close proximity, studies in the US found colonies separated by only about 2.5 meters, with up to 24 colonies at a single structure. Workers are diurnal foragers that use pheromone trails to recruit nestmates to food. However, they do not exhibit mass recruitment like some ants, foraging trails are loose and erratic. Workers require contact with queen and brood to initiate foraging, colonies without queen or brood do not forage. Alates (reproductives) are produced from mid-spring through summer and are attracted to lights at night ^[1][6][8].

Health and Safety Considerations

While B. patagonicus does not bite or sting, they are considered a medical pest concern because laboratory trials showed they can vector Escherichia coli (E. coli) up to 2 meters. This makes them particularly concerning in hospitals, kitchens, and other areas where food is prepared. Practice good hygiene, wash your hands before and after handling the colony or cleaning the enclosure. They are not known to cause structural damage or transmit diseases, but their presence in high numbers can be a nuisance ^[1][8].

Frequently Asked Questions

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References