Formica subpolita

Quick Summary

• Difficulty: Medium
• Origin & Habitat: Western North America, found throughout the western US from Canada to Mexico, particularly common in Nevada, Idaho, Utah, Oregon, and Washington. Inhabits diverse environments from hot desert sands to cooler mountain plains at 4,300-10,800 feet elevation ^[3][2][6].
• Colony Type: Single-queen colonies (monogyne). Queens migrate during early July, digging small surface chambers under rocks to deposit eggs ^[2].
• Size & Growth:
  • Queen: Size data unavailable, inferred from Formica genus patterns to be approximately 9-11mm
  • Worker: Highly polymorphic, inferred from Formica fusca group patterns to be 4-9mm ^[1]
  • Colony: Colonies can become populous under favorable conditions, though high-altitude colonies often remain small with only a few individuals ^[2]
  • Growth: Moderate
  • Development: 6-10 weeks (estimated based on typical Formica development at optimal temperatures) (Development time inferred from genus patterns, Formica species typically take 6-10 weeks from egg to first worker at warm temperatures. Queens dig small surface chambers under rocks and deposit eggs ^[2].)
• Antkeeping:
  • Temperature: Keep at room temperature around 20-24°C. As a cold-climate specialist, they tolerate cooler conditions better than tropical ants. Avoid sustained temperatures above 30°C ^[7][3].
  • Humidity: Moderate humidity. These ants naturally nest under stones in areas with variable moisture, so avoid both very dry and waterlogged conditions. Provide a moisture gradient in the nest.
  • Diapause: Yes, as a cold-climate species from high elevations, they require a winter hibernation period. Keep colonies at 5-10°C for 3-4 months during winter ^[3].
  • Nesting: Prefers nests under stones or with crater mound entrances. In captivity, a naturalistic setup with flat stones over soil, or a Y-tong/plaster nest with chambers works well. Provide access to a foraging area ^[2].
• Behavior: Workers are timid and fast-moving. They are not aggressive and will flee rather than fight. As a cold-climate species, they are more active in cooler temperatures. They forage for seeds, insects, and honeydew. Escape risk is moderate, use standard barrier methods ^[3].
• Common Issues: colonies often fail during hibernation if kept too warm or too wet, maintain cool, stable temperatures around 5-10°C, wild-caught colonies may have parasites including the fungus Laboulbenia formicarum that can affect workers ^[4][5], slow growth compared to tropical ants means beginners may lose patience and overfeed, queen adoption can be difficult, F. subpolita colonies may be taken as slaves by aggressive Formica species if housed nearby ^[2], test tube setups may be too small for established colonies, they need space for granary behavior and multiple chambers, the parasitic wasp Elasmosoma vigilans has been documented parasitizing this species in Colorado ^[2]

Nest Preferences and Housing

In the wild, Formica subpolita nests primarily under stones, with colonies sometimes building distinctive crater mounds 4-10cm in diameter with entrance holes 4-8mm across. Most nests have 1-4 entrance openings, with desert colonies typically having more openings than those in less arid environments ^[2]. Nest chambers usually sit about 18 inches below ground surface, with the number of chambers varying based on colony size. Colonies at high altitude on rocky, vegetationless slopes consisted of only a few individuals, while under more favorable conditions colonies are generally much more populous.

For captive care, a naturalistic setup works best, a flat stone placed over moist soil allows the ants to create their own galleries. Alternatively, a Y-tong (AAC) or plaster nest with narrow chambers and passages scaled to their size provides good visibility. Because they are granivorous, include some fine gravel or sand in the nesting area where they can store seeds. A foraging area should be provided with access to sugar water, protein sources, and seeds. Escape prevention is important but not as critical as for tiny ants, standard barriers work well for these medium-sized ants.

Feeding and Diet

Formica subpolita has a varied diet that includes granivorous, carnivorous, and secretivorous (honeydew-feeding) habits ^[2]. In captivity, offer a diverse diet:

For protein, provide small insects like fruit flies, mealworms, small crickets, or other feeder insects 2-3 times per week. They will also scavenge on dead insects.

For carbohydrates, offer sugar water, honey, or maple syrup. They also readily tend aphids and mealybugs for honeydew if present in the setup.

Seeds can be offered as well, they have been documented storing seeds in nest chambers in the wild. Provide small seeds like millet, chia, or dandelion seeds.

This species is not a specialized predator, so live prey is appreciated but not required. They are opportunistic feeders that will accept a wide variety of foods. Remove uneaten food after 24-48 hours to prevent mold.

Temperature and Seasonal Care

As a cold-climate specialist, Formica subpolita is adapted to cooler temperatures than most ant species. Keep the nest area at room temperature, ideally around 20-24°C. They can tolerate temperatures down to 15°C without issues and are more comfortable in cooler conditions than tropical ants ^[7].

During winter, colonies require a hibernation period. Reduce temperatures to 5-10°C and maintain this for 3-4 months. This mimics their natural cycle in high-elevation western North America where winters are harsh. Do not feed during hibernation, but ensure the nest substrate remains slightly moist.

In summer, avoid overheating. While they can tolerate brief warm periods, sustained temperatures above 30°C can be harmful. Room temperature is generally ideal, no additional heating is typically needed unless your home is very cold.

Behavior and Colony Dynamics

Workers of Formica subpolita are characterized as timid and fast-moving, they will quickly retreat from threats rather than engage in aggressive defense. This is typical of the fusca group species, which generally avoid confrontation ^[3].

Colonies are monogyne, meaning they have a single queen. Queens have been observed migrating during early July in some populations, digging new chambers under rocks to establish new nesting sites ^[2]. This suggests some colony relocation behavior.

The species is highly polymorphic, with workers varying significantly in size within a single colony. Larger workers typically serve as foragers and defenders, while smaller workers handle brood care and internal nest tasks.

Mating occurs through both male aggregation and female calling syndromes, males gather in groups while females release pheromones to attract mates ^[8]. Copulation lasts 28 seconds to 1.6 minutes, with multiple matings observed up to 4 times ^[9].

Health and Common Problems

Several health concerns should be monitored when keeping Formica subpolita:

The parasitic fungus Laboulbenia formicarum can infect workers in the wild. This fungus is one of the smallest Laboulbeniales, reaching up to 0.3mm in total length. Thalli can be extremely abundant on infested workers, though infested workers go foraging seemingly unaffected amid noninfested workers ^[4]. While this typically doesn't kill foragers, it can spread in captivity if wild-caught ants are introduced. Quarantine new colonies before introducing them to existing setups.

The parasitic wasp Elasmosoma vigilans has been documented parasitizing this species in Colorado. This wasp lays eggs in ants, eventually killing the host, difficult to treat in captivity ^[2].

Because this species can be taken as a slave by other Formica species (Formica pergandei, Formica subintegra, Formica puberula), keep them separated from aggressive Formica species ^[2].

Growth is slower than tropical ants, so resist the urge to overfeed. Excess food leads to mold problems, which can be fatal to colonies. Clean the foraging area regularly and remove uneaten food promptly.

Frequently Asked Questions

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References