Lasius platythorax

Lasius platythorax

Lasius platythorax is a small to medium-sized ant native across the Palearctic region, from Western Europe through Central Europe to Western Siberia ^[1]. Workers measure 3-5mm and queens 8-11mm, with a dark brown to black-brown body color ^[2]. This species was only recognized as separate from the common black garden ant (Lasius niger) in 1991,making it one of the more recently described ant species in Europe ^[3]. The two species look very similar, but L. platythorax has distinctly longer, more numerous hairs on its body and prefers much more humid, shaded habitats ^[4].

What makes this species special is its strong preference for forest environments and moist habitats. Unlike its cousin L. niger, which thrives in gardens and urban areas, L. platythorax almost exclusively inhabits woodlands, bogs, and fens ^[5]. It builds nests in rotting wood, under stones, and in mossy tussocks rather than constructing the familiar soil mounds that L. niger builds ^[5]. This species is also notably aggressive when its nest is disturbed, it bites strongly and will defend its colony vigorously ^[6].

Quick Summary

• Difficulty: Easy
• Origin & Habitat: Palearctic region, from Western Europe east to Western Siberia, found in forests, bogs, fens, and moist grasslands ^[1][5]. Prefers humid, shaded environments and avoids open, dry, or human-altered habitats ^[5][7].
• Colony Type: Monogynous colonies (single queen) with documented worker replacement reproductives ^[8]. Colonies can contain up to 10,000 workers ^[9]. Polydomous nesting (multiple nest sites connected) has been reported in some populations ^[2].
  • Colony: Monogyne
  • Founding: Claustral, Pleometrosis
• Size & Growth:
  • Queen: 8-11 mm ^[2]
  • Worker: 3-5 mm ^[2][9]
  • Colony: Up to 10,000 workers ^[9]
  • Growth: Moderate
  • Development: 6-10 weeks (estimated based on related Lasius species) (Development time is temperature-dependent. Larvae can overwinter in all stages ^[10].)
• Antkeeping:
  • Temperature: Keep at 18-22°C. This is a cool-tolerant forest species that prefers temperatures below 25°C, in the wild they thrive in forest soils with mean temperatures of 10-15°C and maximums under 20°C ^[11]. Avoid overheating the nest.
  • Humidity: High humidity required. Keep the nest substrate consistently moist but not waterlogged. This species naturally inhabits damp forest floors and wetlands, drying out is a major threat ^[5]. Provide a water source and mist occasionally.
  • Diapause: Yes, requires winter hibernation. In temperate regions, colonies enter dormancy from roughly October/November through March/April. Keep at 5-10°C during this period, similar to outdoor temperatures in their natural range ^[12].
  • Nesting: Best kept in setups that mimic their natural dead-wood nesting preferences. Y-tong (AAC) nests, plaster nests, or naturalistic setups with rotting wood pieces work well. They do not build soil mounds. Provide access to moist substrate and avoid dry, heated enclosures ^[5][6].
• Behavior: Lasius platythorax is an aggressive defender of its nest and will bite strongly if threatened ^[6]. Workers are active foragers that hunt small insects and tend aphids for honeydew, they form well-defined foraging trails ^[13]. They are primarily nocturnal foragers in some regions, tending aphids at night ^[14]. This species is not a good escape artist compared to smaller ants, but standard escape prevention (fluon on test tube rims) is still recommended. They are generally peaceful toward other ant species when foraging but will defend their nest aggressively ^[14].
• Common Issues: drying out is the biggest threat, these ants need consistently moist conditions, overheating can kill colonies, keep away from direct heat sources above 25°C, wild-caught colonies may carry parasites that cause colony collapse, confusion with L. niger means some keepers may accidentally keep the wrong species, verify identification by habitat preference, queens can be killed by workers during nuptial flight preparation if stressed, handle gently during colony founding

Housing and Nest Setup

Lasius platythorax requires a setup that provides constant moisture and avoids overheating. Test tube setups work for founding colonies, fill one-third with water and plug with cotton, providing a dark area for the queen. For established colonies, Y-tong (AAC) nests or plaster nests with water reservoirs work well because they allow you to maintain humidity ^[5]. Naturalistic setups with a layer of moist soil/peat mix and pieces of rotting wood simulate their natural dead-wood nesting sites. Avoid fully artificial dry nests, this species will struggle and may die. Room temperature (18-22°C) is ideal, they do not need heating unless your room drops below 15°C. Place the nest in a shaded area away from direct sunlight.

Feeding and Diet

Like most Lasius species, these ants are omnivores with a strong sweet tooth. They readily accept sugar water, honey, or diluted maple syrup as their primary energy source. For protein, offer small insects like fruit flies, small crickets, or frozen bloodworms. They are also avid aphid farmers, if you keep them in a naturalistic setup with live plants, they'll tend aphids and collect honeydew ^[14]. Feed sugar sources continuously (a cotton ball with diluted honey or sugar water) and protein 2-3 times per week. Remove uneaten protein after 24 hours to prevent mold. Workers will store honeydew in their social stomachs and share with the colony.

Temperature and Seasonal Care

This is a cool-temperate species that naturally inhabits forest floors with relatively low soil temperatures. Keep the nest area between 18-22°C year-round. They can tolerate brief periods cooler or warmer, but prolonged temperatures above 25°C are harmful. In autumn (around October), reduce temperature gradually to initiate hibernation. Provide a winter rest period of 3-4 months at 5-10°C, a basement, unheated room, or refrigerator (not freezer) works well ^[12]. Do not feed during hibernation but keep the water tube filled so they don't dry out. Resume normal temperatures and feeding in spring.

Colony Founding and Growth

Newly mated queens found colonies independently (claustral founding). After mating during nuptial flights (June-August), the queen seals herself into a small chamber in soil, rotting wood, or under bark ^[14]. She lives entirely on her stored fat reserves while laying eggs and raising the first workers (nanitics). This stage takes 4-8 weeks depending on temperature. Once the first workers emerge, they take over foraging and the colony grows steadily. Growth rate is moderate, expect 2-3 years to reach several hundred workers, and 5+ years to reach thousands. Mature colonies can live for decades with the queen lasting 15-20 years.

Identification and Distinguishing from Lasius niger

Lasius platythorax was only separated from Lasius niger in 1991,so these two species are often confused ^[3]. The key differences: L. platythorax has longer, more numerous standing hairs on its body (especially on the clypeus and scapes), prefers humid forest habitats, and nests in dead wood rather than building soil mounds. L. niger prefers dry, open, often urban habitats and builds characteristic earth mounds. If you collected a queen from a forest or wetland area, it's likely L. platythorax, from a garden or sidewalk crack, it's likely L. niger. Under magnification, L. platythorax workers have sparser clypeal pubescence with longer gaps between hairs ^[4].

Common Problems and Solutions

The biggest killer of Lasius platythorax in captivity is drying out. Their natural habitat is constantly moist forest floor, a dry test tube or nest will kill them quickly. Always provide a water source and check substrate moisture weekly. Overheating is the second major issue, keep them away from windows with direct sun and avoid heat mats unless your room is very cold. If workers are clustering outside the nest area, the nest is likely too dry or too hot. Another problem is stress during founding, newly claustral queens are very vulnerable and should be kept completely dark and undisturbed for the first 4-6 weeks. Finally, ensure you're actually keeping L. platythorax and not the similar L. niger, they have very different care requirements. ^[5][6][12]

Frequently Asked Questions

References