Stereomyrmex horni

Stereomyrmex horni

Stereomyrmex horni is a tiny Myrmicine ant endemic to Sri Lanka, belonging to the tribe Crematogastrini. Workers and males were originally described by Emery in 1901 from specimens collected in Bandarawela, and the genus was established based on these Sri Lankan specimens ^[1]. The queen is ergatoid, meaning she is wingless and serves as a replacement reproductive if the primary queen dies ^[2]. This is an exceptionally rare species, listed as Critically Endangered (CR) on Sri Lanka's National Red List with criteria B2ab(iii) ^[3]. The ant is dark in coloration with typical Myrmicine morphology. What makes this species particularly interesting is its extreme rarity and limited distribution, it has only been encountered a handful of times despite extensive ant surveys across Sri Lanka from 2000-2008 ^[1].

Quick Summary

• Difficulty: Expert
• Origin & Habitat: Endemic to Sri Lanka, found in dry mixed evergreen forest in the North Central Province (Anuradhapura Sanctuary at 108m elevation) and wet zone forests in Western and Southern provinces ^[1][4]. The species can survive in habitats with a wide range of soil moisture conditions and has been found in the absence of leaf litter ^[4].
• Colony Type: Unconfirmed colony structure. The queen is ergatoid (wingless), which typically indicates potential for replacement reproductives within established colonies. Based on typical Myrmicinae patterns, likely single-queen colonies, but this has not been directly studied.
• Size & Growth:
  • Queen: Estimated 4-5mm based on ergatoid queen morphology typical of related Myrmicinae ^[2]
  • Worker: Estimated 2-3mm based on typical genus size range ^[2]
  • Colony: Unknown, no colony size data exists in scientific literature
  • Growth: Unknown, no development data exists for this species
  • Development: Unknown, no direct measurements exist. Based on typical Myrmicinae in tropical conditions, estimated 4-8 weeks at optimal temperature. (This is a pure estimate based on related species, no species-specific data is available)
• Antkeeping:
  • Temperature: Field data shows air temperature 27-30°C and soil temperature 25-29°C across collection sites ^[4]. Keep nest area around 25-28°C as a starting point. This is based on actual field measurements, not laboratory studies.
  • Humidity: Field data shows soil moisture ranging from 6.4% to 36.1% across different forest sites ^[4]. This species tolerates a wide moisture range. Keep substrate moderately moist but not waterlogged, with some variation available.
  • Diapause: Unknown, this is a tropical species from Sri Lanka where temperatures remain warm year-round. Likely no true diapause, but may show reduced activity during cooler periods.
  • Nesting: Ground-nesting species based on nest density studies in forest soils ^[4]. In captivity, a test tube setup or small acrylic/plaster nest would be appropriate. Provide moist soil substrate.
• Behavior: Behavior is unstudied in both wild and captive conditions. Based on typical Myrmicinae behavior, they likely form small colonies and forage on the ground. Escape risk is low given their tiny size, they are not strong climbers. Aggression levels are unknown.
• Common Issues: this species is critically endangered and should not be collected from the wild, ethical concerns about keeping rare endemic species, no captive husbandry information exists, you would be pioneering all care methods with no guidance, field-collected colonies may carry parasites that could kill them in captivity, virtually nothing is known about their diet, feeding may be experimental and uncertain, the ergatoid queen system may affect colony structure in ways we don't understand

Conservation and Ethical Considerations

Stereomyrmex horni is listed as Critically Endangered (CR) on Sri Lanka's National Red List ^[3]. This is one of the rarest ant species in the world, with only a handful of specimens ever collected despite intensive surveys. The species has been found in protected areas including Anuradhapura Sanctuary. For these reasons, wild collection is strongly discouraged and may even be illegal. If you are interested in keeping this species, the only ethical approach would be to work with established captive colonies from responsible breeding programs, though none are known to exist in the antkeeping hobby. This species represents a case where the antkeeping community should prioritize conservation over hobby interest.

Distribution and Habitat

This species is endemic to Sri Lanka, meaning it is found nowhere else on Earth ^[5]. Originally known only from the type locality of Bandarawela in the wet zone, it was later discovered in Anuradhapura Sanctuary in the dry zone North Central Province ^[1]. More recent surveys extended its known range to Western Province (KPFR site) and Southern Province (WFR site) ^[4]. At the Anuradhapura site, it was found in dry mixed evergreen forest at 108m elevation with air temperature around 29.6°C and soil moisture around 6.4% ^[4]. At the wetter KPFR site, air temperature was 27.3°C with much higher soil moisture of 26.6% ^[4]. This demonstrates the species can tolerate a wide range of moisture conditions.

Temperature and Care

Field temperature data provides the best guidance for this species. In their natural habitat, air temperatures ranged from 27-30°C and soil temperatures from 25-29°C across different forest sites ^[4]. Keep the nest area within this range, roughly 25-28°C. A heating cable on one side of the nest can create a gentle gradient. Since this is a tropical species from a warm climate, no hibernation or diapause is expected. However, being a ground-nesting species from Sri Lanka, they likely prefer stable conditions without major temperature fluctuations. Monitor colony behavior, if workers become sluggish, slightly increase temperature, if they avoid the heated area, reduce it.

Nest Preferences and Setup

Field studies show this is a ground-nesting species found in forest soils ^[4]. Nest density was studied using quadrat methods, finding up to 0.6 nests per square meter at one site ^[4]. In captivity, provide a nest setup with moist soil or plaster substrate. A test tube setup with damp cotton works well for founding colonies. For established colonies, a small acrylic or plaster nest with narrow chambers scaled to their tiny size would be appropriate. The wide range of soil moisture conditions they tolerate in the wild (6-36%) suggests they are adaptable, but aim for consistently damp substrate rather than wet or dry extremes.

Behavior and Temperament

The behavior of Stereomyrmex horni has never been studied in detail. Based on its placement in Myrmicinae and the Crematogastrini tribe, it likely exhibits typical ant behaviors: small ground-nesting colonies that forage for food items including nectar, small insects, and honeydew. The ergatoid queen system (wingless queens that can serve as replacement reproductives) is interesting but its implications for captive husbandry are unknown. No information exists on aggression levels, foraging patterns, or colony defense. Given their tiny size and rarity, they are unlikely to be aggressive or difficult to contain. Start with standard Myrmicinae care protocols and adjust based on observed colony behavior. ^[2]

Frequently Asked Questions

References