Polyrhachis brisbanensis

Polyrhachis brisbanensis

Polyrhachis brisbanensis is a medium-sized, striking ant species native to eastern Australia. Workers measure 9.4-10.6mm and are entirely black with dark reddish-brown mandibles. They belong to the ammon species-group within the subgenus Hagiomyrma, characterized by their distinctive spines on the petiole (the narrow waist segment) and a unique patch of dark reddish pubescence on the upper surface of the abdomen. The pronotal dorsum is almost square-shaped, and the petiolar spines are closely spaced and parallel ^[1].

This species is a ground-nesting ant found in open eucalypt forests and woodlands around Brisbane, Queensland. Colonies are relatively small, typically containing 50-60 workers with a single queen. Nests are built under pieces of wood or rocks, with entrance tunnels hidden from view. They are similar in appearance to their close relatives P. ammon and P. brutella, but can be distinguished by their almost quadrate pronotum and the distinctive reddish patch on their gaster ^[1][2].

Quick Summary

• Difficulty: Medium
• Origin & Habitat: Eastern Australia, greater Brisbane region, north to Fraser Island and Cooloola coast, south to the Queensland-New South Wales border, and west to near the Great Dividing Range. Inhabits open eucalypt forests and woodlands, nesting under stones or pieces of wood on the ground ^[1][2].
• Colony Type: Single-queen colonies (monogyne) with small colony size of about 50-60 workers ^[1].
  • Colony: Monogyne
  • Founding: Claustral
• Size & Growth:
  • Queen: 10.38-10.89 mm ^[1]
  • Worker: 9.42-10.58 mm ^[1]
  • Colony: About 50-60 workers per colony ^[1]
  • Growth: Moderate, small colony size suggests moderate growth rate
  • Development: Unknown, no specific development data available for this species. Based on typical Polyrhachis patterns, expect 6-10 weeks at optimal temperature. (Development timeline not directly studied. Related Polyrhachis species typically take 6-10 weeks from egg to worker.)
• Antkeeping:
  • Temperature: Estimated 22-26°C based on Australian eucalypt forest habitat. Provide a gentle temperature gradient allowing workers to self-regulate. Room temperature within this range should be suitable
  • Humidity: Moderate humidity around 50-70%. Being a ground-nesting species from southeastern Queensland, they likely prefer substrate that is damp but not waterlogged. Provide a moisture gradient in the nest
  • Diapause: Likely required, as a temperate to subtropical Australian species, they probably need a winter rest period. However, specific diapause requirements are unconfirmed
  • Nesting: Ground-nesting species. In captivity, they do well in naturalistic setups with soil substrate or in Y-tong/plaster nests with chambers scaled to their medium size. Provide a layer of substrate they can dig in and pieces of cover material (cork, stones) as they prefer covered nest entrances ^[1][2]
• Behavior: Generally calm and non-aggressive for a Polyrhachis species. Workers are moderately active foragers. They are medium-sized ants with a moderate escape risk, ensure your formicarium has secure barriers and small enough mesh to contain them. They may be more active during warmer months. Their small colony size makes them manageable for observation without being overwhelmed by numbers ^[1].
• Common Issues: small colony size means they are sensitive to disturbance, handle gently during transfers, ground-nesting behavior requires appropriate substrate depth and cover material in the nest, winter dormancy requirements are not well documented, monitor colony for seasonal slowdowns, escape prevention should be adequate for medium-sized ants, standard barriers usually sufficient, limited availability in the antkeeping hobby means established colonies may be difficult to find

Housing and Nest Setup

Polyrhachis brisbanensis is a ground-nesting species that naturally builds nests under stones, logs, or other ground cover. In captivity, they do well in naturalistic setups with a soil or sand substrate layer deep enough for them to excavate chambers. You can also use Y-tong (acrylic) nests or plaster nests with appropriately sized chambers for medium-sized ants around 10mm.

Because they naturally nest under cover, include flat stones, cork pieces, or other cover materials in your setup. This mimics their natural preference for protected nest entrances. A naturalistic terrarium-style setup works particularly well, fill part of the container with soil substrate and add pieces of wood or stone as cover. Keep the substrate moderately moist but not waterlogged.

For the outworld (foraging area), a simple setup with a water test tube as a humidity source and a feeding station works well. They are moderate foragers and will come out to collect protein and sugar sources. ^[1][2]

Feeding and Diet

Like most Polyrhachis species, these ants are omnivorous. They likely forage for honeydew, nectar, and small insects in the wild. In captivity, offer a varied diet including sugar water or honey as a constant energy source, and protein sources like small crickets, mealworms, or other feeder insects.

Feed protein foods 1-2 times per week, adjusting based on colony size and appetite. Remove any uneaten prey after 24-48 hours to prevent mold. Keep a sugar source available at all times, a small dish with cotton wool soaked in sugar water or a drop of honey works well.

Their small colony size means they won't consume large quantities of food. Start with small portions and increase as your colony grows. ^[2]

Temperature and Seasonal Care

As a species from the Brisbane region of Queensland, these ants are accustomed to warm temperate to subtropical conditions. Aim for temperatures in the range of 22-26°C. Room temperature within this range should be suitable, but you may need a small heating cable or mat on one side of the nest during cooler months to maintain optimal temperatures.

Provide a temperature gradient so workers can self-regulate by moving between warmer and cooler areas of the nest. This is especially important if your room temperature fluctuates. A heating cable placed on top of the nest (never underneath where it could dry out the substrate) can help maintain stable temperatures.

Regarding winter care, being from southeastern Queensland (a region with cool but not freezing winters), they likely benefit from a reduced temperature period in winter. However, their specific diapause requirements are not well documented. If you notice your colony becoming less active in winter, reduce temperatures slightly to around 15-18°C for 2-3 months.

Behavior and Colony Dynamics

Polyrhachis brisbanensis forms relatively small colonies of 50-60 workers with a single queen. This is characteristic of the species and differs from some other Polyrhachis that can form larger colonies. The small colony size makes them well-suited for observation and care, you can watch the entire colony without being overwhelmed by numbers.

Workers are described as having abundant golden hairs and pubescence, giving them a somewhat fuzzy appearance. They are not particularly aggressive and handle well during nest checks. However, always use proper escape prevention as they are medium-sized ants that can still find their way out of inadequately sealed setups.

The species is part of the ammon group within Hagiomyrma, characterized by their distinctive petiolar spines. These spines are more pronounced in workers than queens and serve as a key identification feature. ^[1]

Growth and Development

The development timeline for P. brisbanensis has not been directly studied. Based on typical Polyrhachis patterns and their medium size, expect approximately 6-10 weeks from egg to first worker at optimal temperatures. Larger Polyrhachis species often take longer, but this smaller species should develop at a moderate pace.

Colonies reach about 50-60 workers in natural nests. This relatively small maximum colony size means you won't need to upgrade to massive setups as the colony grows. However, it also means growth may seem slow compared to faster-breeding species.

Queens measure 10.38-10.89mm, making them only slightly larger than workers. This is typical for Polyrhachis where queens are not dramatically larger than workers. The queen is dealate (wingless) after mating, as indicated by the dealate queen found in natural colonies. ^[1]

Frequently Asked Questions

References