Iridomyrmex obsidianus

Iridomyrmex obsidianus

Iridomyrmex obsidianus is a small, strikingly glossy ant native to New Caledonia, a French territory in the South Pacific. Workers measure 0.73-0.84mm in head width with extremely shiny dark chocolate-colored cuticle and pale yellow setae ^[1]. The most distinctive feature is their long antennal scape, which extends about three times its diameter beyond the back of the head, this easily separates them from the similar-looking Iridomyrmex calvus that shares the same island ^[1]. These ants were first described by Emery in 1914 from specimens collected on Mount Humboldt at 1600m elevation ^[2]. As a member of the Dolichoderinae subfamily, they belong to the Leptomyrmecini tribe, which contains some of the most recognizable ants in Australia and the Pacific region.

Quick Summary

• Difficulty: Medium
• Origin & Habitat: New Caledonia, a tropical island in the South Pacific with humid, warm climate. Specimens collected from Mount Humboldt at 1600m elevation suggest they tolerate cooler conditions at higher altitudes ^[2][3].
• Colony Type: Colony structure is unconfirmed. Many Iridomyrmex species form multi-queen colonies, but specific data for this species is lacking.
• Size & Growth:
  • Queen: Undocumented, no queen measurements available
  • Worker: 0.73-0.84mm head width,0.85-0.90mm head length ^[1]
  • Colony: Unknown, no colony size data available
  • Growth: Unknown, estimated moderate based on tropical Dolichoderine patterns
  • Development: Unconfirmed, estimated 4-8 weeks based on typical tropical ant development (No direct development data exists for this species. Estimates based on related tropical Iridomyrmex species.)
• Antkeeping:
  • Temperature: Aim for 22-26°C, warm but not extreme. New Caledonia has a tropical climate with temperatures ranging from 20-30°C year-round in lowlands, cooler at elevation. Provide a gentle temperature gradient.
  • Humidity: Moderate to high, New Caledonia is humid (60-80%). Keep nest substrate consistently moist but not waterlogged. Provide a humidity gradient so ants can choose their preferred zone.
  • Diapause: Unknown, tropical species may not require formal hibernation, but a slight cool period during winter months may be beneficial.
  • Nesting: No specific nesting data exists. In captivity, standard test tubes or acrylic nests work well. Given their small size and shiny cuticle, they likely nest in soil or rotting wood in nature.
• Behavior: Behavior is undocumented in scientific literature. Most Iridomyrmex species are generalist foragers and can be moderately aggressive when defending their territory. Their small size means escape prevention is critical, they can squeeze through tiny gaps. They likely forage in trails and recruit nestmates to food sources, as is typical of the genus.
• Common Issues: tiny size makes escape likely without fine mesh barriers, no published care guidelines means starting points are estimates, colony structure unknown, may be single or multi-queen, development timeline unconfirmed requires observation-based adjustments, limited availability in antkeeping hobby

Appearance and Identification

Iridomyrmex obsidianus workers are tiny ants, measuring just 0.73-0.84mm in head width ^[1]. Their most striking feature is the extremely glossy, shiny cuticle that gives them a polished appearance, this is how they got their scientific name 'obsidianus' (referring to obsidian volcanic glass). The body color is described as shining dark chocolate, with pale yellow erect hairs scattered across the body ^[1].

The key identifying feature is the long antennal scape, the antenna's first segment extends about three times its diameter beyond the rear margin of the head ^[1]. This makes them easy to distinguish from their close relative Iridomyrmex calvus, which also lives on New Caledonia but has a shorter scape. No queen or male descriptions are available in the scientific literature.

Natural History

This species is known only from New Caledonia, a tropical island in the South Pacific about 1,200km east of Australia ^[3]. The type specimen was collected on Mount Humboldt at approximately 1600m elevation, suggesting this species prefers higher-altitude or cooler microclimates within the island's tropical environment ^[2].

Beyond these basic collection records, no detailed biological studies exist for Iridomyrmex obsidianus. The genus Iridomyrmex as a whole contains species that are typically generalist foragers, often forming large colonies with multiple queens. Many Australian Iridomyrmex species are known for their aggressive defense of foraging territories and their ability to dominate ground-level food sources.

Housing and Nest Setup

Given their tiny size (under 1mm workers), you'll need excellent escape prevention. Use fine mesh on any ventilation holes and ensure all connections between outworld and nest are sealed. Test tube setups work well for founding colonies, with a water reservoir providing humidity. For established colonies, a small acrylic or plaster nest with appropriately scaled chambers works better than oversized formicaria.

Since we have no specific nesting data, provide options: a moist area for brood chambers and a slightly drier area for the queen to rest. A humidity gradient lets the ants self-regulate. Keep nesting materials dark to simulate the underground conditions they likely prefer.

Feeding and Diet

No specific dietary studies exist for this species. Based on typical Iridomyrmex behavior, they are likely generalist foragers that collect honeydew from aphids and scale insects, hunt small insects, and will accept sugar sources. Feed a mix of sugar water or honey as a constant energy source, and protein sources like small fruit flies, pinhead crickets, or other appropriately sized prey items.

Because workers are so tiny, prey items must be very small. Springtails and other micro-arthropods are likely ideal. Offer food 2-3 times per week, removing uneaten prey within 24 hours to prevent mold.

Temperature and Seasonal Care

New Caledonia has a warm tropical climate with average temperatures ranging from 20-30°C depending on season and elevation. Since the type specimen came from 1600m elevation, they may tolerate slightly cooler conditions than pure lowland tropical ants. Aim for a nest temperature of 22-26°C, with a slight gradient allowing workers to move between warmer and cooler areas.

Whether they need a winter rest period is unknown. Tropical ants often slow down slightly during cooler months but don't enter true diapause. If your room temperature drops below 20°C during winter, consider mild supplemental heating, but avoid dramatic temperature swings.

Frequently Asked Questions

References