Myrmica rubra

Myrmica rubra - "European Fire Ant"

Myrmica rubra is a small, reddish-brown ant native to the Palearctic region, ranging from Ireland and Portugal across Europe to Siberia ^[1][2]. Workers measure 3.5-5 mm and possess a noticeable sting that delivers a painful venom comparable to a stinging nettle ^[1][3]. In nature, they favor moist habitats, nesting under stones, in rotting wood, or within moss tussocks, and are frequently found in meadows, gardens, and forest edges ^[2][4]. What makes this species truly unusual is its social structure: colonies are typically polygynous with multiple queens, and they produce two distinct queen morphs, large macrogynes that found colonies independently and tiny microgynes that act as intraspecific social parasites within established nests ^[5][6]. They are also specialized predators of springtails, using a unique 'tip-and-run' hunting technique ^[7]. In North America, they are an invasive pest forming dense supercolonies that displace native ants ^[1][8].

Quick Summary

• Difficulty: Medium
• Origin & Habitat: Native to the Palearctic temperate zone (Europe to Siberia), found in moist meadows, woodlands, and anthropogenic habitats, invasive in northeastern North America ^[1][2]
• Colony Type: Facultatively polygynous colonies with multiple queens (up to 600+ observed) and polydomous nesting, produces two queen morphs, macrogynes and parasitic microgynes ^[1][5]
  • Colony: Optionally polygyne, Supercolonial
  • Founding: Semi-claustral, Pleometrosis
• Size & Growth:
  • Queen: 4.5-6 mm (macrogynes), microgynes ~2.4-2.6 mm mesosoma length ^[1][6]
  • Worker: 3.5-5 mm ^[2]
  • Colony: Up to 10,000+ workers, occasionally exceeding 20,000 in large polycalic systems ^[2][1]
  • Growth: Moderate (split brood cycle with rapid and diapausing larvae) ^[9]
  • Development: 6-10 weeks at 22-24°C for rapid brood, overwintering larvae complete development the following spring ^[9][10] (Northern populations develop faster than southern populations at the same temperature ^[10]. Colonies produce both rapid-developing summer workers and slower diapausing larvae that overwinter ^[9].)
• Antkeeping:
  • Temperature: Keep at 20-24°C for optimal brood development, avoid overheating as lethal temperature is approximately 39°C ^[10][11]. Northern populations tolerate cooler conditions better than southern ones ^[10].
  • Humidity: High humidity required, this is the most moisture-loving Myrmica species. Keep nest substrate damp but not waterlogged, they require humid conditions to forage actively ^[2][4].
  • Diapause: Yes, required for the overwintering portion of the brood. Maintain at 3-5°C for 3-4 months with moist substrate ^[9][12].
  • Nesting: Use Y-tong (AAC) or plaster nests with small chambers and moist substrate. Naturalistic setups with flat stones, rotting wood, or moss work well ^[2][1].
• Behavior: Aggressive and territorial with a painful sting. Workers forage day and night using trail pheromones (3-ethyl-2,5-dimethylpyrazine) to recruit nestmates ^[13]. They are specialized predators of springtails but also tend aphids for honeydew and visit flowers for nectar ^[7][2]. Infected workers exhibit phototaxis and withdraw from the nest to die, reducing disease transmission ^[14].
• Common Issues: tiny workers can escape through the smallest gaps, use fine mesh barriers and Fluon-coated walls, painful stings require caution during maintenance, desiccation risk if humidity drops below preferred moist conditions, fungal infections (e.g., Metarhizium) can spread quickly in stagnant, overly wet conditions without ventilation ^[14], invasive in North America, never release outdoors in regions where established ^[1][8], colonies may accept multiple queens but can show aggression during initial introduction

Nest Preferences and Setup

In the wild, Myrmica rubra nests under flat stones, in rotting wood, under bark, or within grass and moss tussocks, often constructing small soil mounds ^[2][1]. They prefer shaded, moist microhabitats and are commonly found in meadows with high groundwater, riparian areas, and gardens ^[2]. For captive colonies, use Y-tong (AAC) or plaster nests that maintain humidity well. Chambers should be small and tight-fitting to their size. Provide a moisture gradient by keeping one side of the nest damper than the other, and offer nesting materials like small stones or wood pieces to simulate natural conditions ^[1].

Feeding and Diet

Myrmica rubra is omnivorous but shows specialized predatory behavior on springtails (Collembola), using a 'tip-and-run' attack where the ant bends its abdomen and head toward the thorax and jumps onto the prey ^[7]. They also frequently tend aphids and scale insects for honeydew, and visit flowers for nectar ^[2]. In captivity, provide live springtails as a primary protein source, supplemented with small insects like fruit flies or mealworm pieces. Offer sugar water or honeydew substitutes constantly. They require both protein for brood development and carbohydrates for worker energy ^[7][2].

Temperature and Humidity Requirements

Keep colonies at 20-24°C for optimal brood production, with a slight gradient allowing ants to thermoregulate ^[10]. Avoid temperatures above 30°C for extended periods, as their lethal temperature is approximately 39°C ^[11]. They are oligothermophilic (preferring cooler conditions) and hygrophilic (moisture-loving), requiring high humidity to survive ^[4]. Maintain nest substrate damp to the touch but not flooded. During winter, provide a diapause period at 3-5°C for 3-4 months to allow overwintering larvae to complete development properly ^[9][12].

Colony Founding and Development

Queens are semi-claustral, meaning they must leave the nest to forage during founding rather than surviving entirely on stored fat reserves ^[12][15]. Colonies exhibit a split brood cycle: queens lay eggs in early summer that either develop rapidly into workers within 6-10 weeks, or grow slowly, enter diapause as third-instar larvae, and complete development the following spring ^[9]. This results in two cohorts of workers, summer-born and spring-born. Northern populations develop faster than southern populations at the same temperature, an adaptation to shorter summers ^[10].

Macrogynes and Microgynes

Myrmica rubra produces two distinct queen morphs. Macrogynes are large (4.5-6 mm), fly during nuptial flights in August-September, and found colonies independently or join existing nests ^[1][5]. Microgynes are miniature queens (mesosoma ≤1.9 mm) that mate near the nest and act as intraspecific social parasites, infiltrating established colonies, particularly older ones, and producing up to 40 times more gynes than macrogynes while contributing fewer workers ^[5][6]. Microgynes were previously described as a separate species (M. microrubra) but are now recognized as a genetically distinct parasitic morph of M. rubra ^[6][16].

Behavior and Temperament

These ants are highly aggressive and possess a painful sting used for defense and subduing prey ^[1][3]. Workers forage both day and night, recruiting nestmates to food sources using trail pheromones from their venom glands ^[13]. When infected with fungal pathogens like Metarhizium, workers exhibit altered behavior: they become attracted to light, lose attraction to social cues, and withdraw from the nest to die alone, reducing disease spread to nestmates ^[14]. They are effective competitors and can displace other ant species from food sources ^[8].

Invasive Status and Ecological Impact

Introduced to North America around 1900, Myrmica rubra is invasive in the northeastern United States and southeastern Canada, forming dense supercolonies with nest densities reaching 1.24 nests/m² compared to 0.02-0.13 in its native range ^[1][8]. These populations are multicolonial (not unicolonial) and aggressively displace native ant species, reducing local biodiversity ^[8][17]. If you live in North America, never release captive colonies outdoors. In their native European range, they are important hosts for endangered Maculinea butterflies and play key roles in seed dispersal and soil health ^[18][2].

Frequently Asked Questions