Pseudomyrmex obtusus

Pseudomyrmex obtusus

Pseudomyrmex obtusus is a medium-sized ant species belonging to the Pseudomyrmecinae subfamily, part of the goeldii species group. Workers measure 0.86-0.93mm in head length and 0.71-0.78mm in head width, making them relatively large for a twig ant ^[1]. They have a distinctive appearance with a broad head (CI 0.80-0.85), elongate eyes, and a matte body texture from dense fine punctulation. The coloration is medium to dark brown with a striking contrast, the petiole, postpetiole, and most of the gaster are a contrasting light yellowish-brown, while the mandibles, tibiae, and tarsi are also lighter than the rest of the body ^[1]. This species is a generalist dead twig inhabitant, nesting in dead twigs of various plants including Ficus trees, thorny vines, and other woody plants ^[1][2].

This species is notable for its timid demeanor compared to some of its more aggressive relatives in the Pseudomyrmex genus ^[1]. Found across the Neotropical region from Costa Rica to Peru and Brazil, they inhabit rainforests, rainforest edges, and successional pastures near forested areas ^[1][2]. Unlike some Pseudomyrmex that have specialized relationships with acacia plants, P. obtusus is a generalist that simply uses dead twigs as nesting sites. Their broad head and distinctive sculpture help separate them from other species in the goeldii group.

Quick Summary

• Difficulty: Medium
• Origin & Habitat: Neotropical region, Costa Rica, Panama, Venezuela, French Guiana, Suriname, Peru, and Brazil. Inhabits rainforests, rainforest edges, and successional pastures near rainforest ^[1][2].
• Colony Type: Colony structure is unconfirmed. Based on typical Pseudomyrmex patterns, likely single-queen colonies nesting in dead twigs ^[1].
  • Colony: Monogyne
  • Founding: Claustral
• Size & Growth:
  • Queen: Estimated 8-10mm based on genus patterns, direct measurements not available
  • Worker: 0.86-0.93mm head length,0.71-0.78mm head width ^[1]
  • Colony: Likely small to moderate, typical for twig-nesting Pseudomyrmex, estimated under 500 workers
  • Growth: Moderate, inferred from tropical Pseudomyrmex patterns
  • Development: 6-10 weeks estimated based on related Pseudomyrmex species at tropical temperatures (Development time is estimated, no specific study exists for this species. Tropical temperatures (24-28°C) likely accelerate development compared to temperate species.)
• Antkeeping:
  • Temperature: Keep at 24-28°C. This is a tropical species from rainforest habitats, so warmth is essential. A heating cable on one side of the nest creates a gradient allowing workers to regulate their temperature ^[1].
  • Humidity: Keep moderately humid, around 60-80%. These ants naturally live in rainforest environments, so they appreciate moisture but need good ventilation to prevent mold. Mist occasionally and provide a water tube, but ensure the nest doesn't become waterlogged.
  • Diapause: No, this is a tropical species that does not require hibernation. Maintain warm temperatures year-round ^[1].
  • Nesting: Natural nesting is in dead twigs, they've been collected from dead twigs of Ficus sp., thorny vines, and other woody plants ^[1]. For captivity, a Y-tong (acrylic) nest with narrow chambers works well, or a naturalistic setup with wooden twigs/branches. Avoid large open spaces, they prefer tight, enclosed chambers scaled to their size.
• Behavior: P. obtusus has a timid demeanor compared to many other Pseudomyrmex species ^[1]. They are generalist twig inhabitants and not associated with specific host plants like some acacia-ant relatives. Workers are relatively active and will forage for small prey. Their small size means escape prevention is important, use fine mesh and tight-fitting lids. While not as aggressive as some Pseudomyrmex, they can still bite if threatened.
• Common Issues: tropical species requires constant warmth, cold temperatures below 20°C can slow or stop brood development, escape prevention is important due to small worker size, use fine mesh barriers, small colony sizes mean overfeeding can lead to mold problems in the nest, wild-caught colonies may be stressed from collection and may have parasites, dry conditions can cause colony decline, monitor humidity levels carefully

Nest Preferences and Housing

Pseudomyrmex obtusus is a classic twig-nesting ant. In the wild, they exclusively inhabit dead twigs, researchers have collected colonies from dead twigs of Ficus trees, thorny vines, and various unidentified woody plants ^[1]. This means they prefer tight, enclosed spaces rather than open foraging areas. For captive housing, a Y-tong (acrylic) nest with narrow chambers works well, or you can create a naturalistic setup with actual wooden twigs/branches inserted into the formicarium. The chambers should be appropriately sized for their worker size (under 1mm). Avoid large, open spaces in the nest as these ants prefer to stay concealed in tight quarters. The outworld should be simple with minimal clutter, a small foraging area is sufficient for this species.

Feeding and Diet

Like other Pseudomyrmex species, P. obtusus is likely predatory and will accept small live prey. In captivity, offer small insects like fruit flies, pinhead crickets, and small mealworms. They probably also consume honeydew and nectar in the wild, so offering a sugar source like honey water or sugar water occasionally is worthwhile, though protein should be the primary food. Feed small prey items 2-3 times per week, adjusting based on colony size and consumption rate. Remove any uneaten prey after 24-48 hours to prevent mold. A constant water source should be available, a test tube with water and a cotton plug works well.

Temperature and Seasonal Care

As a tropical species from Central and South American rainforests, P. obtusus requires warm temperatures year-round. Keep the nest area at 24-28°C for optimal brood development ^[1]. Temperatures below 20°C can significantly slow or halt development, and prolonged cold can kill the colony. Use a heating cable or heating mat on one side of the nest to create a temperature gradient, allowing workers to move to warmer or cooler areas as needed. Place the heating element on top of the nest rather than underneath to avoid drying out the nest too quickly. Since this is a tropical species, no hibernation or diapause is required, maintain consistent warm conditions throughout the year.

Behavior and Temperament

One distinguishing characteristic of P. obtusus is its timid demeanor, this species is notably less aggressive than many other Pseudomyrmex, which are often fierce defenders of their host plants ^[1]. Workers are relatively small and active, foraging for prey in the surrounding area. While they can bite if threatened, they are not particularly aggressive toward keepers. Their small size (under 1mm) means they can escape through very small gaps, so escape prevention is important. Use fine mesh (at least 0.5mm) on any ventilation holes and ensure all lids fit tightly. Despite their small size, they are relatively visible due to their contrasting coloration, dark brown body with light yellowish-brown gaster makes them stand out against substrate.

Colony Establishment and Growth

Colony founding behavior has not been directly documented for P. obtusus, but based on typical Pseudomyrmex patterns, the queen likely seals herself into a small chamber within a dead twig (claustral founding) and raises the first brood alone using stored fat reserves ^[1]. The first workers (nanitics) will be smaller than mature workers and may take 6-10 weeks to emerge at optimal tropical temperatures. Colony growth is likely moderate, Pseudomyrmex colonies typically remain relatively small (under 500 workers) even at maturity because they nest in confined twig spaces. When collecting from the wild, look for colonies in dead twigs hanging from vegetation or lying on the forest floor. Wild colonies may be stressed from collection and could have parasites, so quarantine and careful observation is recommended.

Frequently Asked Questions

References