Lasius fallax

Lasius fallax

Lasius fallax is a small, pale yellow to light brown ant native to western North America, ranging from Washington and Montana south to Arizona. Workers measure just 0.44-0.70mm in pronotal width, making them one of the smaller Lasius species. They have a distinctive very small eye with fewer than 35 ommatidia (usually around 20), and their tibiae have erect or semierect hairs on all surfaces. Queens are larger at 1.38-1.55mm head width. This species belongs to the flavus clade (subgenus Cautolasius) and is closely related to Lasius brevicornis, Lasius nearcticus, and Lasius talpa, with which it shares many intermediate characteristics. In the wild, colonies nest under stones in rocky sands or loam soils, often in forested areas like pinyon-juniper and ponderosa pine habitats, particularly near riparian zones.

Quick Summary

• Difficulty: Easy
• Origin & Habitat: Western North America, Washington, Idaho, Montana, Wyoming, Colorado, Utah, Arizona. Also confirmed in Saskatchewan, Canada. Nests under stones in rocky sands or loam soils in forested areas (pinyon-juniper, ponderosa pine) and riparian habitats ^[1][2][3].
• Colony Type: Colony structure is unconfirmed. Based on related species in the flavus clade, likely forms single-queen colonies (monogyne), though some Lasius species can be multi-queen (polygyne).
  • Founding: Claustral
• Size & Growth:
  • Queen: 1.38-1.55mm head width ^[1]
  • Worker: 0.44-0.70mm pronotal width ^[1]
  • Colony: Unknown for this specific species. Related Lasius species typically reach 5,000-10,000 workers.
  • Growth: Moderate, estimated based on related species in the flavus clade
  • Development: 6-10 weeks estimated based on typical Lasius development patterns (Development time inferred from related Lasius species. Temperature-dependent, warmer conditions accelerate development.)
• Antkeeping:
  • Temperature: Keep around 20-24°C. Related Lasius species in this clade prefer moderate temperatures. Provide a temperature gradient so ants can self-regulate.
  • Humidity: Moderate humidity around 50-60%. Keep the nest substrate moist but not waterlogged. These ants nest under stones in nature, indicating they prefer somewhat damp but not saturated conditions.
  • Diapause: Yes, likely requires winter hibernation. Related Lasius species typically need 3-4 months of cold period (5-10°C) during winter.
  • Nesting: Test tube setups work well for founding colonies. For established colonies, use a formicarium with moist soil or plaster. They naturally nest under stones in compact soil, so provide a substrate they can dig into. Y-tong nests with narrow chambers also work for their small size.
• Behavior: Generally calm and non-aggressive. Workers are small but active foragers. They likely tend aphids for honeydew and collect small insects as protein sources, similar to other Lasius species. Escape risk is moderate due to their small size, use standard barriers but no special escape prevention needed beyond standard measures.
• Common Issues: small worker size means they can escape through standard test tube cotton if not properly packed, colonies may be slow to establish during founding phase, patience is required, winter hibernation is essential, skipping it can weaken or kill colonies, overheating is more dangerous than cold, avoid temperatures above 28°C, wild-caught colonies may contain parasites that can decimate captive colonies

Nest Preferences and Housing

Lasius fallax naturally nests under stones in compact soils like rocky sands and loam. For captive colonies, start with a standard test tube setup for the founding queen. Fill the tube with water, plug with cotton, and place the queen inside. Keep it dark and undisturbed for 2-4 weeks until eggs appear. Once the colony reaches 20-30 workers, you can move them to a formicarium. A Y-tong (acrylic) nest with narrow chambers works well given their tiny worker size. Alternatively, a naturalistic setup with moist soil and a flat stone on top mimics their natural nesting conditions. Whatever setup you choose, ensure the nest chamber is humid but not wet, these ants avoid flooded conditions. ^[1]

Feeding and Diet

Like other Lasius species, Lasius fallax is omnivorous with a preference for sugar sources and protein. Offer sugar water (1:1 ratio) or honey diluted with water as a constant carbohydrate source. For protein, provide small insects like fruit flies, pinhead crickets, or mealworm pieces. They will also accept honeydew if you have access to aphid colonies. Feed protein sources 2-3 times per week, and keep sugar water available at all times. Remove uneaten prey after 24-48 hours to prevent mold. During hibernation, reduce or eliminate feeding entirely.

Temperature and Seasonal Care

Maintain nest temperatures around 20-24°C. These ants are adapted to temperate climates and do not require high heat. A heating cable on one side of the nest creates a temperature gradient, allowing workers to move between warmer and cooler areas. During summer, room temperature is usually sufficient. In winter, colonies require a hibernation period of 3-4 months at 5-10°C. Place the colony in an unheated garage, basement, or refrigerator (not freezer) during this time. Gradually cool them down over 1-2 weeks in autumn, and gradually warm them up in spring. Skipping hibernation weakens colonies and shortens queen lifespan.

Behavior and Colony Dynamics

Lasius fallax workers are small but active and efficient foragers. The colony will establish a network of trails for foraging to sugar sources and protein prey. Queens are claustral, they seal themselves in a chamber and raise the first brood alone without leaving to forage. The first workers (nanitics) are smaller than mature workers but quickly expand the colony. Workers likely exhibit typical Lasius behaviors including tending aphids for honeydew and recruiting nestmates to food sources through chemical trails. Colonies grow moderately, expect several months before the first workers appear, then steady growth over 1-2 years to reach several hundred workers.

Frequently Asked Questions

References