Lasius fuliginosus
Temperature
20–26 °C
Humidity
55–75%
Colony size
50,000–500,000
Queen size
6–7 mm
Worker size
4–5 mm
Hibernation temp
6 °C
Diet
Care Guide
Deep, glossy black and almost metallic in the right light, *Lasius fuliginosus* is a true giant among the genus *Lasius*, commanding colonies that can swell to half a million workers. The queen, measuring a modest 6–7 mm, is only slightly larger than her workers (4–5 mm), yet she possesses one of the most fascinating and demanding founding strategies in European myrmecology: she is a social parasite. A newly mated queen must infiltrate a colony of another *Lasius* species (typically *Lasius niger* or *Lasius platythorax*), kill or enslave the host queen, and use the host workers to raise her first generation of pure *fuliginosus* brood. This delicate, high-stakes process is why keeping this species is reserved for experienced keepers.
The workers are unmistakable once you look closely. Their bodies are incredibly smooth and shiny, almost polished, and they give off a faint, sweet, lemon-like scent when alarmed or crushed — a chemical signature that helps them blend into host colonies. As the colony grows, these ants become bold and energetic foragers, constantly on the move in search of honeydew and live insects. Their diet is varied but heavily dependent on liquid carbohydrates; they will accept sugar water, diluted honey, and especially honeydew from coccids if you can provide them a small plant. Protein in the form of crickets, fruit flies, or mealworms is essential for brood development, and they will eagerly dismantle any insect they can overpower.
Care difficulty
Keeping *Lasius fuliginosus* is an expert-level undertaking, primarily due to the parasite founding stage and the immense colony size that eventually demands a very large setup. The first year is the most precarious — you must provide a suitable host colony (often reared beforehand) or purchase a pre‑founded queen. Once established, the colony grows vigorously, but their requirement for a deep, damp nest with minimal disturbance remains constant.
Housing
A formicarium for *Lasius fuliginosus* must offer a dark, humid nesting space with plenty of soil or plaster to maintain a stable 55–75% humidity. They prefer temperatures between 20 and 26°C, with a slight warmth gradient. The outworld should be generous, as these ants are industrious foragers that will fill every corner with activity. A large water source — or a carefully humidified nest chamber — is critical; dryness quickly stresses the colony. Hibernation is mandatory: from late autumn through winter, the colony must be cooled gradually to around 6°C for at least three months. Without this cold period, the queen will exhaust her energy reserves and the colony will fail.
First days after purchase
Upon receiving your *Lasius fuliginosus* colony (ideally after the founding stage), place the formicarium in a quiet, vibration‑free spot. Do not disturb the nest for at least a week. Offer a drop of sugar water on a piece of cotton wool and a small insect for protein, but avoid overfeeding. Observe from a distance — any bright light or sudden movement can cause stress. Patience is everything with this species. Once the workers begin exploring and foraging confidently, you know your care is on the right track.