Acromyrmex lundii

Acromyrmex lundii

Acromyrmex lundii is a medium-sized leaf-cutting ant native to southern South America, found in Argentina, Brazil, Paraguay, and Uruguay ^[1][2]. Workers measure 5.5-7 mm and display a distinctive thimble-like punctate sculpture across the body ^[3]. In nature, they construct elaborate thatch mounds interlaced with tree roots, housing underground fungus gardens up to 40 cm deep and 1.8 meters long ^[4]. These ants are significant agricultural pests throughout their range, damaging cereal crops and gardens ^[5][6]. They also serve as hosts for the social parasite Pseudoatta argentina and the cockroach Attaphila bergi ^[7][8].

These ants display a peculiar innate behavior: when navigating without visual cues, they show a strong preference for turning left (counter-clockwise), choosing left branches approximately twice as often as right branches in maze experiments ^[9]. They also use carbon dioxide concentrations as spatial cues, positioning their fungus gardens at soil depths where CO2 levels favor fungal growth ^[10]. Unlike some leaf-cutting ants, they may have reduced associations with antibiotic-producing bacteria, instead relying on metapleural gland secretions to protect their fungus gardens ^[5].

Quick Summary

• Difficulty: Expert
• Origin & Habitat: Southern South America (Argentina, Brazil, Paraguay, Uruguay), found in forests, agricultural areas, and the Caldenal district ^[1][2][11]
• Colony Type: Single-queen (monogyne) colonies, genetic analysis confirms obligate monogyny with queens mating with 1-6 males ^[12]
  • Colony: Monogyne
• Size & Growth:
  • Queen: Unknown, not specified in available research
  • Worker: 5.5-7 mm, medium workers weigh 3-5 mg ^[3][9]
  • Colony: Unknown in worker numbers, mature nests are large structures exceeding 1.5 meters in length ^[4]
  • Growth: Unknown
  • Development: Unknown, not documented in research (Development depends on fungus garden health and temperature)
• Antkeeping:
  • Temperature: 25°C in laboratory conditions, maintain stable temperatures between 22-28°C with heating cables if necessary ^[13]
  • Humidity: Above 45% relative humidity, maintain damp but not waterlogged fungus substrate ^[13]
  • Diapause: No, tropical/subtropical species active year-round
  • Nesting: Requires specialized fungus garden setup, clear containers with ventilation work better than standard test tubes ^[4][14]
• Behavior: Leaf-foragers using trunk trails, innate left-turning navigation bias, use CO2 gradients to position gardens, agricultural pest behavior on dicot plants ^{[15][9][10][5]}
• Common Issues: escovopsis fungus disease can rapidly destroy the fungus garden and kill the colony ^[5][16]., phorid parasitoids can infest colonies and decimate worker populations if fine mesh screens are not used ^[17]., fungus garden failure due to inappropriate leaf species or contaminated plant material ^[4]., slow initial growth until the fungus garden establishes, requiring patience and stable conditions.

Nest Architecture and Fungus Garden Management

In nature, Acromyrmex lundii builds distinctive thatch mounds interlaced with tree roots, creating a main fungus garden chamber 35-40 cm high and 30-35 cm wide that hangs from the roots, surrounded by 10-15 smaller chambers ^[4]. The ants position these gardens near the soil surface where carbon dioxide levels favor fungal growth, excavating more actively in soils with 0-7% CO2 and avoiding higher concentrations that inhibit digging ^[10]. Workers dynamically adjust nest architecture based on contents, they enlarge chambers only if they contain fungus, create round chambers when brood is present, and dig tunnels when brood is absent ^[1]. They also opportunistically deposit excavated soil in unused spaces to effectively downsize their nest when needed ^[1].

In captivity, you cannot use standard test tubes. Instead, provide a clear container setup with a Leucoagaricus gongylophorus fungus garden inoculated from an established colony ^[14]. The substrate should consist of dried leaves and oat flour. Maintain humidity above 45% to prevent the fungus from drying out, but ensure adequate ventilation to prevent stagnant air ^[13]. Place the garden where workers can easily access it, and expect them to modify the space based on fungus volume and brood placement.

Feeding and Foraging

Acromyrmex lundii forages exclusively on dicot plants, cutting leaf fragments and transporting them back to the nest along established trunk trails ^[4][15]. In the wild, they are major agricultural pests in central Argentina, damaging cereal crops, gardens, and horticultural fields ^[5][6]. Laboratory colonies are typically fed with bramble leaves and honey-water mix ^[13].

In captivity, offer fresh dicot leaves such as bramble, rose, oak, or citrus daily. The ants do not eat the leaves directly, they chew them into a pulp to cultivate their mutualistic fungus, feeding on specialized fungal structures called gongylidia ^[14]. Remove uneaten or dried leaf material promptly to prevent mold growth. Provide a constant sugar source such as honey water or sugar water in a feeding station ^[13].

Temperature and Environmental Control

Laboratory colonies thrive at 25°C with greater than 45% relative humidity under a 12:12 light:dark cycle ^[13]. Maintain stable conditions, fluctuations can stress the fungus garden and lead to colony decline. If supplemental heating is necessary, place the heating cable or mat on top of the nest rather than underneath to prevent drying the garden from below and causing condensation issues.

These ants use CO2 concentrations as spatial cues to position their fungus gardens at optimal depths ^[10]. While you do not need to replicate soil CO2 levels in captivity, ensure the setup has some air exchange to prevent CO2 buildup, but not so much ventilation that humidity drops below acceptable levels.

Disease and Parasite Management

Acromyrmex lundii faces severe threats from Escovopsis weberii, a parasitic fungus that attacks the mutualistic fungus garden ^[16][5]. Infected gardens show reduced weight and increased worker mortality. Unlike some other leaf-cutting ants, this species may lack associations with antibiotic-producing Actinobacteria (Pseudonocardia), instead relying on metapleural gland secretions for protection ^[5]. This potentially makes them more vulnerable to fungal diseases.

Phorid flies (Apocephalus neivai and Myrmosicarius catharinensis) parasitize workers with natural rates around 1.5-1.6% in the wild ^[17]. In captivity, use fine mesh screens (0.5mm or smaller) on all ventilation to exclude these parasitoids. Pathogenic fungi such as Beauveria bassiana and Purpureocillium lilacinum can cause 70-75% mortality in laboratory conditions ^[2][16]. Maintain strict hygiene, use sterilized nest materials, and quarantine any new plant material before introducing it to the colony.

Behavioral Navigation

Workers exhibit a remarkable innate preference for turning left (counter-clockwise) when navigating without visual cues. In Y-maze experiments without visual stimuli, approximately twice as many ants chose the left branch over the right (46 left vs 22 right) ^[9]. They also display optomotor responses, following moving vertical stripes, and align toward fixed vertical landmarks ^[9].

While this left-turning bias is fascinating, it has minimal practical impact on captive care except to note that circular foraging arenas might trigger continuous looping behavior. The ants primarily rely on pheromone trails for foraging, with visual cues serving as a fallback option when other cues are absent ^[9].

Frequently Asked Questions

References