Stereomyrmex horni

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 tolerates a wide range of soil moisture conditions and has been found in areas with little to no leaf litter ^[4].
• Colony Type: Colony structure is unconfirmed. The queen is ergatoid (wingless) ^[2], but whether colonies are single-queen or multiple-queen is unknown.
• Size & Growth:
  • Queen: size data unavailable
  • Worker: size data unavailable
  • Colony: Unknown
  • Growth: Unknown
  • Development: Unknown, no direct measurements exist (No development data is available for this species)
• Antkeeping:
  • Temperature: Field data shows air temperatures of 27-30°C and soil temperatures of 25-29°C across collection sites ^[4]. Keep the nest area around 25-28°C as a starting point. This guidance is based on field measurements, not laboratory studies.
  • Humidity: Field data shows soil moisture ranging from 6.4% to 36.1% across different forest sites, indicating a wide tolerance ^[4]. Keep the substrate moderately moist but not waterlogged, and provide a humidity gradient for the ants to choose from.
  • Diapause: Unknown, this is a tropical species from Sri Lanka where temperatures remain warm year-round. Likely no true diapause is needed, but activity may slow during cooler periods.
  • Nesting: Ground-nesting species found in forest soils ^[4]. In captivity, use a test tube setup for founding, then a Y-tong or plaster nest with narrow chambers scaled to their tiny size. Provide moist soil substrate and avoid acrylic nests.
• Behavior: Behavior is unstudied in both wild and captive conditions. As a member of the tribe Crematogastrini, they likely use a smear defense, wiping venom on enemies rather than piercing flesh. Escape risk is high due to their tiny size, they require a secure formicarium with tight-fitting lids. Aggression levels are unknown.
• Common Issues: this species is Critically Endangered and should not be collected from the wild, wild collection may be illegal in Sri Lanka ^[3]., 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 will be experimental and uncertain., the ergatoid queen system may affect colony structure in ways not yet understood., escape risk is severe due to tiny size, requiring careful enclosure design.

Conservation and Ethical Considerations

Stereomyrmex horni is listed as Critically Endangered 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. Wild collection is strongly discouraged and may 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 Y-tong 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 the tribe Crematogastrini, it likely uses a smear defense mechanism, wiping venom onto enemies with a flattened stinger rather than piercing flesh. The ergatoid queen system (wingless queens) is interesting but its implications for captive husbandry are unknown. No information exists on aggression levels, foraging patterns, or colony defense. Escape risk is high due to their tiny size, use a tight-fitting lid on the formicarium and seal any gaps. Start with standard Myrmicinae care protocols and adjust based on observed colony behavior. ^[2]

Frequently Asked Questions

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References