Lasius fuliginosus

Introduction

Lasius fuliginosus, also known as the "Jet Black Ant," is one of the most biologically complex and fascinating species in the temperate regions of Europe and Asia. They are easily recognized by their extremely shiny, jet-black appearance and their disproportionately large, heart-shaped heads. Beyond their looks, their lifestyle is extraordinary: they are "carton" builders, constructing their nests from a mixture of masticated wood, sugary secretions, and a specific fungus (Cladosporium myrmecophilum) that helps reinforce the structure.

Keeping Lasius fuliginosus is considered a "master class" in ant keeping. They are hyper-social, forming massive colonies with multiple queens and intricate pheromone trails. They have a distinct, pleasant odor (often described as citrusy or like citronella) which they use for chemical communication and defense. While challenging to start, a thriving colony of Jet Black Ants is a spectacle of biological engineering and social coordination.

Taxonomy & Classification

• Family: Formicidae
• Subfamily: Formicinae
• Genus: Lasius
• Species: Lasius fuliginosus (Latreille, 1798)

They belong to the Dendrolasius subgenus. Their classification is unique because they are "temporary social parasites." A Lasius fuliginosus queen cannot start a colony on her own; instead, she must infiltrate a colony of another Lasius species (typically Lasius umbratus, which itself is a parasite of Lasius niger) and take over the nest.

Appearance & Morphology

The workers of Lasius fuliginosus are monomorphic, ranging from 4-6mm. The queen is slightly larger (7-9mm) but has a very bulky thorax and a broad head.

The most striking feature is their "ultra-glossy" finish. They are perhaps the shiniest ants in the world, appearing like polished black beads. Their heads are wide and heart-shaped, housing the powerful muscles needed for their constant "carton" chewing and high-intensity foraging. Their movement is fluid and they tend to move in very thick, well-defined columns.

Natural Habitat & Distribution

Found throughout Europe and temperate Asia, these ants are primarily associated with old-growth forests and parks with mature trees (particularly oak and birch). They usually nest in the hollows of trees or in the roots, where they build their characteristic black carton nests. They are famous for their "ant roads"—permanent, pheromone-soaked trails that can stretch for dozens of meters across the forest floor to their favorite aphid-infested trees.

Colony Structure & Life Cycle

Colonies are often polygynous (containing multiple queens) and can reach staggering sizes, sometimes numbering over 100,000 workers. Because they are social parasites, the founding process in captivity is extremely difficult and involves "introducing" a queen to a host colony. However, once the fuliginosus workers take over, the colony becomes very robust. They are long-lived and have a very strong social cohesion, with workers frequently sharing food (trophallaxis).

Dietary Requirements

Lasius fuliginosus are "sugar addicts." In the wild, they derive the vast majority of their nutrition from the honeydew of aphids.

• Sugars (Critical): They require a constant, 24/7 supply of sugars. Honey-water, sugar-water, and fruit nectars are essential. If they run out of sugar, the colony can decline rapidly.
• Proteins: While they prefer sugars, protein is necessary for the larvae. They like small, soft-bodied insects like fruit flies or freshly killed small crickets.
• Special Note: They are very fond of "liquids" and will often ignore solid food in favor of liquid protein or sugar supplements.

Housing Conditions: Temperature & Humidity

They prefer temperate conditions and a stable environment. They are quite sensitive to extreme heat and desiccation.

The carton nest they build in the wild is naturally humid; in captivity, you must ensure their formicarium never dries out.