Atta bisphaerica

Atta bisphaerica

Atta bisphaerica is a large fungus-growing ant native to Brazil, commonly called the grass-cutting ant or "saúva mata-pasto." Queens reach approximately 25 mm in length, while workers range from tiny 3 mm minors to 15 mm soldiers ^[1]. They inhabit the Brazilian Cerrado savanna and Atlantic Forest regions, building distinctive nests in open pastures and sunny areas across São Paulo, Minas Gerais, Rio de Janeiro, and Goiás ^[2][3]. Unlike their famous leaf-cutting relatives, these ants are strict grass specialists, cutting monocots like sugarcane, corn, and pasture grasses rather than broad leaves ^[4][5].

What makes Atta bisphaerica unique among Atta species is their specialized diet and nest architecture. They construct vast underground networks containing up to thousands of spherical fungus chambers arranged beneath a single flat mound of loose soil, reaching depths of 2.5 meters but spreading extensively sideways ^[6][7][8]. Their fungus gardens have a distinctive particulate, brittle texture with visible grass fragments and require precise conditions to thrive: stable temperatures around 25°C and high humidity ^[9][10]. In nature, they forage almost exclusively at night, with activity peaking between 15-20°C, and they maintain complex trail systems radiating from the nest to harvest grasses ^[11][7].

Quick Summary

• Difficulty: Expert
• Origin & Habitat: Brazil (São Paulo, Minas Gerais, Rio de Janeiro, Goiás, Espírito Santo, Mato Grosso), specifically the Cerrado savanna and open pasturelands in sunny, well-drained areas ^[2][3][12].
• Colony Type: Single-queen colonies (monogyne) with highly polymorphic worker castes ranging from tiny minors to large soldiers ^[1].
  • Colony: Monogyne
  • Founding: Claustral
• Size & Growth:
  • Queen: Approximately 25 mm ^[1].
  • Worker: Highly polymorphic: minors approximately 3 mm, foragers approximately 10 mm, soldiers approximately 15 mm ^[1].
  • Colony: Up to several million workers with nests containing thousands of chambers ^[13][8].
  • Growth: Slow to Moderate, founding takes 80-100 days before first workers emerge, but colonies can grow large over several years ^[14][15].
  • Development: 10-14 weeks (estimated from 80-100 day claustral founding period) ^[14]. (Queens seal themselves in for 80-100 days during founding, raising the first workers alone on stored body reserves ^[14].)
• Antkeeping:
  • Temperature: Maintain around 20-25°C for the nest area. Activity peaks at 15-20°C in nature, but fungus gardens need stable warmth around 25°C ^[7][11][10].
  • Humidity: High humidity essential for fungus garden health. Keep substrate moist but not waterlogged, the fungus garden should feel damp and maintain pH around 6.3 ^[9][10].
  • Diapause: No, this is a tropical species active year-round without winter rest ^[11].
  • Nesting: Requires very large formicarium with deep substrate and multiple spherical chambers to accommodate extensive fungus gardens. Natural nests reach 2.5 m deep with hundreds of chambers ^[6][7].
• Behavior: Nocturnal foragers that cut grasses and transport them along well-defined trail systems ^[11][16]. Moderately aggressive, soldiers will bite when disturbed but are less aggressive than Atta sexdens ^[2]. Workers show organized trail use with loaded and unloaded workers occupying different lanes ^[16].
• Common Issues: fungus garden collapse from feeding incorrect plant material, they require fresh grasses, not dicot leaves or citrus ^[4][5]., massive space requirements, colonies need room for hundreds of fungus chambers as they grow ^[7][8]., extremely high founding mortality, over 90% of queens die during the founding stage in nature ^[15][18]., susceptibility to phorid fly parasitoids that attack foraging workers ^[19]., difficulty accepting artificial diets or baits compared to other leaf-cutters ^[4].

Natural Nest Architecture and Captive Housing

In nature, Atta bisphaerica builds distinctive nests with a single flat or slightly raised mound of loose soil, unlike the tall chimneys of other Atta species ^[7][2]. The internal structure consists of hundreds to thousands of spherical chambers arranged in clusters, located between 15 cm and 2.5 m deep, with most chambers concentrated in the upper meter ^[6][7]. Chambers range from small (8 cm diameter) to large (over 50 cm), connected by tunnels approximately 2 cm high and 2-3 cm wide ^[6].

For captive keeping, this architecture presents significant challenges. You must provide extensive vertical space with multiple chambers to accommodate the fungus garden as it grows. A setup with deep, spherical chambers connected by narrow tunnels works best, think large Y-tong or plaster nests with removable sections for monitoring. The nest must maintain high humidity (damp substrate) while allowing some ventilation to prevent CO2 buildup, as natural nests have passive ventilation through the mound structure ^[17]. Because colonies can eventually occupy thousands of chambers, you will need to expand the setup significantly as the colony grows, potentially requiring multiple interconnected formicaria for mature colonies.

The Fungus Garden and Diet

Atta bisphaerica is a strict grass-cutter (monocot specialist), which fundamentally differentiates their care from other leaf-cutters. They forage on grasses like jaraguá grass (Hyparrhenia rufa), sugarcane, corn, and rice, and will refuse many dicot leaves including citrus pulp that other Atta species accept ^[4][5]. Their fungus gardens have a distinctive particulate, brittle appearance with visible grass fragments 4-7 mm long, rather than the mashed leaf paste seen in other species ^[9][10].

The fungus garden requires precise conditions: temperature stable at 24-25°C, pH around 6.3,and high humidity ^[9][10]. The ants maintain a biphasic garden structure, a peripheral sector with fresh green fragments where rapid growth occurs, and a core sector with older, pale yellow material ^[10]. You must provide fresh grass clippings daily, preferably from pasture grasses or cereals. Avoid woody plants or broad leaves. The garden produces sugars (glucose, xylose) and polyols (mannitol, sorbitol) that the ants consume ^[9][10]. Never let the garden dry out or overheat, as this kills the symbiotic fungus and dooms the colony.

Temperature and Environmental Needs

These ants prefer moderate temperatures despite living in tropical Brazil. In nature, foraging activity peaks at 15-20°C, and they remain active in cooler weather when other Atta species stop working ^[7][11][2]. However, the fungus garden itself needs warmth around 24-25°C to thrive ^[10].

In captivity, maintain the nest area at 20-25°C with a gentle gradient, slightly cooler near the foraging area (18-22°C) and warmer in the fungus chambers (24-25°C). Use a heating cable on one side of the nest, positioned on top to avoid drying out the substrate from below. Avoid temperatures above 30°C, which can stress the fungus. Humidity should remain high (damp substrate) year-round, as they do not experience dry seasons in their native habitat and show no diapause ^[11].

Colony Founding and Early Development

Founding Atta bisphaerica is extremely challenging. After the nuptial flight, queens seal themselves in a small chamber 8-9 cm deep and remain claustral (enclosed) for 80-100 days, living entirely on stored body fat while raising the first workers and establishing the fungus garden ^[14][15]. During this period, mortality is catastrophic, over 90% of queens die in nature, with survival rates as low as 0.09% to 0.2% ^[15][18].

If you obtain a founding queen, provide a small, dark chamber with moist soil or plaster at 24-25°C. Do not disturb her for at least three months. She will need fresh grass fragments to inoculate with fungus carried from her parent colony in her infrabuccal pocket ^[13]. First workers (nanitics) emerge after approximately 10-14 weeks, smaller than subsequent workers. The colony remains fragile for the first year, with high mortality rates continuing until the colony reaches several hundred workers ^[15].

Behavior and Foraging Patterns

Atta bisphaerica forages almost exclusively at night, starting at dusk with peak activity between 23:00 and midnight during dry months, though they may shift to earlier evening activity (18:00-19:00) in wet seasons ^[11]. They form extensive trail systems radiating from the nest, typically 0.5-20 meters long and 3-6 cm wide, with loaded workers and outbound workers using different lanes to avoid collisions ^[16][7].

Workers cut grass fragments averaging 33 mm long and weighing about 15 mg, carrying them back to the nest ^[2]. They are less selective about load size than other leaf-cutters, maximizing energy return rate rather than individual load efficiency ^[4]. Soldiers defend the nest aggressively when disturbed, producing audible stridulation (chirping sounds) when confined ^[2]. Watch for phorid flies (Apocephalus attophilus, Myrmosicarius grandicornis, Neodohrniphora bragancai) which parasitize foraging workers by laying eggs in their heads or abdomens ^[19].

Frequently Asked Questions

References