Polyrhachis lachesis

Polyrhachis lachesis

Polyrhachis lachesis is an Australian ant belonging to the subgenus Hagiomyrma. Workers are relatively large at 7-8mm total length, with a distinctive appearance featuring pronotal humeri (shoulders) that are produced into dilated, dorsally shallowly concave, rounded prominences, a key identifying feature. They are light to medium reddish-brown with darker shading on the head and mesosoma, and narrow black markings along various body margins. This species inhabits open eucalypt forests and savannah woodlands in northern Queensland, from Lakefield on Cape York Peninsula south to Gladstone, preferring bare ground without grass cover for nesting sites ^[1][2]. Unlike many Formicinae ants, they spin cocoons around their pupae ^[3][4].

Quick Summary

• Difficulty: Medium
• Origin & Habitat: Northern Queensland, Australia, open eucalypt forests and savannah woodlands, preferring bare ground without grass cover ^[1][2]
• Colony Type: Colony structure is unconfirmed, likely single queen (monogyne) based on typical genus patterns, but not directly studied
• Size & Growth:
  • Queen: ~8.37 mm ^[1], only one specimen measured
  • Worker: 7.06-8.21 mm total length, HL 1.84-1.96 mm ^[1]
  • Colony: Unknown, no colony size data available
  • Growth: Moderate, estimated based on similar Polyrhachis species
  • Development: Estimated 6-10 weeks at optimal temperature based on related species in the genus (No direct development data available for this species, estimates based on typical Polyrhachis patterns)
• Antkeeping:
  • Temperature: Keep at 24-28°C as a starting range. These are Australian tropical/subtropical ants that prefer warm conditions. Adjust based on colony activity, workers should be active and foraging. A gentle heat gradient allows them to regulate their temperature
  • Humidity: Moderate humidity around 50-70%. As ground-nesting ants from savannah/woodland areas, they prefer drier conditions than rainforest species. Allow the nest substrate to dry partially between water additions. Provide a water tube but avoid oversaturation
  • Diapause: Likely a minor winter slowdown given their Queensland distribution, but full hibernation is probably not required. Reduce feeding and keep slightly cooler (around 18-20°C) during winter months if colony shows reduced activity
  • Nesting: Subterranean ground-nesters, they prefer bare soil without grass cover ^[1]. In captivity, a naturalistic setup with soil or a Y-tong/plaster nest works well. Provide deep enough substrate for them to create tunnels. They spin cocoons, so the nest should have dry enough conditions that mold won't destroy the pupae ^[3][4]
• Behavior: Generally calm and non-aggressive compared to many ant species. Workers are moderately active foragers. They are ground-nesting so they may not climb extensively on plants or smooth surfaces. Escape prevention should be moderate, they are large enough that standard barriers work well, but they can still climb smooth surfaces. They are not known for stinging and are considered docile ^[2].
• Common Issues: colonies may fail if kept too humid, these are savannah species that prefer drier conditions, lack of development data means keepers must estimate conditions, observe colony behavior and adjust, cocoon-spinning means pupae are vulnerable to mold in overly humid nests, wild-caught colonies may have parasites that are difficult to detect, slow establishment period, don't panic if colony seems inactive during founding

Housing and Nest Setup

Polyrhachis lachesis is a subterranean ground-nesting species that naturally prefers bare ground without grass cover ^[1]. In captivity, you can house them in a naturalistic setup with a deep soil layer (at least 5-10cm) allowing them to excavate their own tunnels, or use a Y-tong (acrylic) nest with compact chambers. Since they spin cocoons ^[3][4], keep the nest moderately dry to prevent mold from destroying the pupae. A plaster nest can work but should be allowed to dry between waterings. These are medium-large ants (7-8mm workers) so they need appropriately sized chambers. Provide an outworld for foraging with a water tube and feeding station.

Feeding and Diet

Polyrhachis ants are typically omnivorous, feeding on honeydew, small insects, and nectar in the wild. In captivity, offer a mix of sugar sources (honey water, sugar water) and protein (small crickets, mealworms, fruit flies). Since they are ground-nesting ants from relatively dry habitats, they may not need constant sugar water, offer it a few times per week and remove any uneaten portions to prevent mold. Protein should be offered 2-3 times per week depending on colony size. Observe your colony's preferences and adjust accordingly. Fresh fruit and occasional treats can be accepted. ^[2]

Temperature and Seasonal Care

As an Australian species from the Cape York/Gladstone area, Polyrhachis lachesis prefers warm conditions. Keep the nest area at 24-28°C as a starting point. A heating cable on one side of the nest can create a temperature gradient, allowing ants to regulate their own temperature. Place the heating on top of the nest, not underneath, to avoid evaporating moisture too quickly. During winter in temperate climates, you may notice reduced activity, this is normal for many Australian species. A slight temperature reduction to around 18-20°C during winter months is appropriate if the colony shows signs of slowing down. Full hibernation is likely not required given their tropical/subtropical range. ^[2]

Behavior and Handling

Polyrhachis lachesis is generally considered a calm, docile species. Workers are moderately active and will forage in the outworld for food. They are not aggressive and do not pose a sting threat to keepers. Their large size (7-8mm) makes them easy to observe. They spin cocoons around their pupae ^[3][4], which is unusual for Formicinae ants and indicates they have more developed brood care. When moving or transferring colonies, handle gently as with any ant species. They are not known escape artists due to their size, but standard escape prevention (fluon on rim edges, tight-fitting lids) is always recommended.

Frequently Asked Questions

References