Liometopum occidentale

Liometopum occidentale - "Western Velvety Tree Ant"

Liometopum occidentale is a large, polymorphic dolichoderine ant native to western North America, ranging from southern Washington through California to Baja California, Mexico. Workers are bicolored with a dark brown head and gaster and a lighter golden-yellow to light brown mesosoma, measuring 2.9-5.1mm. Queens are substantial at 10.5-12mm. These ants form massive colonies of 40,000-60,000 workers and create extensive foraging trails that can stretch over 60 meters, sometimes reaching 185 meters in length. They are a dominant species in oak and pine forests of the southwestern US, known for their aggressive defense when disturbed, they emit a distinctive rotten coconut-like odor and will bite. They are opportunistic omnivores with a strong preference for sugar solutions, and they tend hemipterans (aphids and scale insects) for honeydew. Colonies are speculated to be polydomous (multiple nest sites) and may have multiple queens ^[1][2][3].

Quick Summary

• Difficulty: Medium
• Origin & Habitat: Native to western North America (Washington, Oregon, California, Baja California). Found from sea level to over 1700m elevation in coastal regions. Prefer to nest in crevices of oaks, alders, elms, cottonwoods, and creosote, in soil, underneath bark of dead trees, and under rotten logs. Recently reported nesting in urban homes, underneath insulation or between walls ^[1][2][3].
• Colony Type: Likely polydomous (multiple connected nest sites) with possibly multiple maternally-related queens. Colonies can reach 40,000-60,000 workers. Workers are polymorphic (varying in size from 1.4-5.2mg). Queen number is not definitively confirmed, some evidence suggests multiple queens based on mtDNA analysis, but this needs further study ^[2][3].
• Size & Growth:
  • Queen: 10.5-12.0 mm ^[1]
  • Worker: 2.9-5.1 mm ^[1]
  • Colony: 40,000-60,000 workers ^[2][3]
  • Growth: Moderate
  • Development: Unknown (Annual productivity is 2-2.8 kg of brood per year for colonies with 4-8 year lifespan ^[3]. Development timeline has not been directly studied.)
• Antkeeping:
  • Temperature: Keep nest area around 20-24°C. Workers forage at 24-38°C in the wild and are active from 8-38°C. In captivity, a gentle gradient allowing them to choose their preferred temperature works well. In late summer when temperatures exceed 35°C, they become nocturnal in the wild ^[3].
  • Humidity: Moderate humidity. They nest in tree crevices and soil, not in extremely wet or dry conditions. Provide a moist nest chamber but avoid waterlogging. They have relatively high body water content (68.9%) compared to some related species ^[3].
  • Diapause: Yes, they are adapted to seasonal temperate climates. Nuptial flights occur throughout May, suggesting a winter rest period is needed. Keep them cool (around 10-15°C) for 3-4 months during winter ^[3].
  • Nesting: In captivity, they do well in naturalistic setups with multiple chambers or in Y-tong/plaster nests. They prefer tight, dark spaces that mimic tree crevices. Provide dead wood, cork, or similar materials they can nest in. Given their large colony size and polydomous nature, they need more space than typical small ants. Outworld should be spacious with multiple foraging stations ^[1][2].
• Behavior: Highly aggressive toward other ant species and will defend vigorously. When disturbed, they emit a pungent rotten coconut-like odor and resort to biting. They form massive foraging trails extending 60m or more in the wild, traveling mostly underground in shallow galleries or leaf litter. Workers are polymorphic, some are much larger than others. They are generalist scavengers and predators, and they actively tend aphids and scale insects for honeydew. They have excellent trail-forming behavior and will establish persistent foraging routes. Escape risk is moderate, they are not tiny but are agile climbers. Use standard barrier methods ^[1][2][3].
• Common Issues: colonies can reach 40,000-60,000 workers requiring significant space, ensure your setup can accommodate large colony growth, aggressive toward other ant species, keep them isolated from other ant colonies, emit strong pungent odor when disturbed, normal defensive behavior, not an issue, sensitive to Argentine ant competition, avoid keeping in areas where Argentine ants have invaded, polymorphic workers mean varying sizes, all workers consume similar amounts of sugar regardless of size (about 0.25mg per worker) ^[3]

Housing and Nest Setup

Liometopum occidentale requires more space than typical ants due to their massive colony sizes. In the wild, colonies can reach 40,000-60,000 workers with foraging areas covering up to 2,000 m². For captivity, start with a standard test tube setup for founding colonies, but plan to expand to a larger formicarium as the colony grows. They prefer naturalistic setups with dead wood, cork, or multiple chambers that mimic their natural tree crevice nesting sites. A Y-tong or plaster nest with multiple connected chambers works well. The outworld should be spacious, these ants form long foraging trails and need room to move. Provide multiple feeding stations since they are trail-formers. Ensure the nest has dark, tight spaces they can retreat to ^[1][2][3].

Feeding and Diet

These ants are opportunistic omnivores with a strong preference for sugar sources. Laboratory tests show they strongly prefer 25% sucrose, glucose, and honey solutions, these were consumed most heavily during both day and night trials. They consume about 0.25mg of 25% sucrose water per worker regardless of their size. They also accept protein baits, with anchovy being particularly popular. In the wild, they tend hemipterans (aphids and scale insects) for honeydew and actively hunt small insect prey. For captivity, provide sugar water (sucrose or honey at 25%) constantly, and offer protein sources like mealworms, crickets, or other small insects 2-3 times weekly. They will also accept fruit and other sweet substances. During hot summer months (above 35°C), they become nocturnal foragers in the wild, adjust feeding times accordingly if your colony shows this behavior ^[4][3].

Temperature and Seasonal Care

Keep the nest area at roughly 20-24°C with a gentle gradient allowing workers to choose their preferred temperature. In the wild, foragers are active at temperatures between 24-38°C and have been observed foraging at temperatures as low as 8°C. They are most active during early summer both day and night, but in late summer when daytime temperatures exceed 35°C, they switch to nocturnal foraging. This means you should provide a heat source on one side of the outworld during summer but allow them to escape to cooler areas. During winter, they require a diapause period, keep them cool at around 10-15°C for 3-4 months. Nuptial flights occur throughout May in the wild, so timing your hibernation to allow for spring mating flights is important ^[3].

Behavior and Defense

Liometopum occidentale is highly aggressive toward other ant species and will vigorously defend its territory. When threatened, workers emit a distinctive pungent odor described as rotten coconut-like (sometimes confused with the odorous house ant, Tapinoma sessile) and resort to biting. They form massive, persistent foraging trails, some trails in the wild have been observed in the same location for over two years without changing. Workers are polymorphic, meaning they come in different sizes, but surprisingly all workers consume similar amounts of sugar regardless of their size. They produce alarm pheromones that can affect related ant species like Tapinoma sessile and Forelius pruinosus. Colonies show some aggression toward each other based on geographic distance, ants from sites less than 1km apart show minimal aggression, while colonies more than 8km apart show significantly higher aggression levels ^[1][2][3].

Competition and Ecological Considerations

This native species is negatively impacted by invasive Argentine ants (Linepithema humile). Studies show they rarely co-occur with Argentine ants in the wild, when Argentine ants invade an area, Liometopum occidentale populations decline or disappear entirely. They are considered a habitat or resource specialist and compete poorly with the more aggressive Argentine ant. In aggression trials, Argentine ants initiated aggression against L. occidentale in 42-53% of interactions depending on how long the invasion has been established. If you live in an area where Argentine ants are present, be especially careful about escape prevention, if these ants were to escape and establish in areas with Argentine ants, they would face significant competitive pressure. They are highly aggressive toward other native ant species as well ^[5][3][6].

Frequently Asked Questions

References