Lasius brunneus (The Brown Tree Ant)

Introduction

Lasius brunneus, commonly known as the Brown Tree Ant, is a specialized and fascinating member of the genus Lasius. While its more famous relative, Lasius niger, is a generalist of gardens and sidewalks, Lasius brunneus is a true master of the woodland canopy and the interior of living trees. Known for its discreet lifestyle and its sophisticated bicolored appearance, this species is a key inhabitant of ancient European forests and parklands. It is one of the few Lasius species that spends the majority of its life away from the soil, focusing its activities on the trunks and branches of mature trees.

For ant keepers, Lasius brunneus offers a unique "arboreal" experience within a familiar genus. They are generally more timid and elusive than other Lasius, which adds a layer of mystery and challenge to their care. Their striking bicoloration—a brownish-red thorax contrasting with a dark head and gaster—makes them one of the most attractive Lasius species to keep. Watching a colony of Brown Tree Ants navigate a wood-based habitat is like having a miniature piece of an ancient forest on display.

Taxonomy and Distribution

Lasius brunneus belongs to the subfamily Formicinae and the subgenus Lasius (sensu stricto). It is part of a group of species that have evolved to exploit arboreal niches, moving away from the soil-nesting habits of most of their relatives. Its name "brunneus" (Latin for "brown") refers to the distinctive coloration that sets it apart from the uniform black or yellow of other common Lasius. It is a highly specialized species that is often used by biologists as an indicator of high-quality, mature woodland habitats.

Their distribution covers most of Europe and parts of Western Asia, following the extent of the temperate deciduous forest belt. They are primarily found in ancient woodlands, orchards, and old parklands where mature trees like oaks, elms, and poplars provide the necessary habitat. Unlike Lasius niger, they are rarely found in disturbed or urban environments, preferring the stable and humid conditions of the forest interior.

Physical Characteristics

Lasius brunneus is a monomorphic species, with workers typically measuring between 3.5mm and 5mm. The queen is larger and more robust, measuring around 7-9mm. Their most distinguishing feature is their bicoloration: the head and gaster are a dark brownish-black, while the thorax is a distinct, lighter reddish-brown or orange-brown. This color pattern is very consistent and makes them easy to identify among other Lasius.

Their bodies are sleek and built for life on vertical surfaces. They have strong legs for climbing and relatively large eyes for an ant of their size, which helps them navigate the complex three-dimensional environment of a tree's bark and branches. They possess a "formic acid" gland for defense, but they are generally less aggressive than their soil-nesting cousins, relying more on their agility and ability to hide within crevices to avoid threats.

Colony Behavior and Social Structure

Colonies of Lasius brunneus are strictly monogynous (one queen) and can grow to include several thousand workers. They are famous for their "shy" and "secretive" behavior. In the wild, they often nest inside the dead heartwood of living trees or under thick layers of bark. They create intricate tunnel systems within the wood, which protect them from predators and environmental extremes. They are primarily active during the day but are rarely seen in the open, preferring to move within the fissures of the bark.

Socially, they are highly cooperative and maintain very organized nests. They are specialized "aphid farmers," but unlike L. niger, they focus on tree-dwelling aphids that live on the leaves and branches of their host trees. They are also known for their long-term stability; a colony can inhabit the same tree for many years, slowly expanding their nest as the wood decays. In captivity, they are fascinating to watch as they meticulously explore every crevice of their habitat.

Diet and Foraging

Lasius brunneus is an omnivore with a very high demand for carbohydrates. Their primary food source in the wild is honeydew from tree-dwelling aphids. In captivity, they should be provided with a constant supply of sugar water or honey water. They are also quite fond of specialized ant jellies and sweet fruits. Because they are arboreal, they are very efficient at finding sugar sources placed high up in their outworld.

Protein is essential for the growth of the larvae and the health of the queen. They are opportunistic scavengers and will accept small feeder insects such as fruit flies, small crickets, and mealworms. They are not aggressive hunters and often prefer dead or incapacitated prey. A varied diet of protein and sugars, provided in an outworld that offers climbing opportunities, will ensure a healthy and thriving colony.

Life Cycle and Reproduction

The development from egg to adult worker in Lasius brunneus takes about 6 to 9 weeks, depending on the temperature. Like all Formicinae, they pupate within silk cocoons. The workers are very protective of the brood, often keeping them in the deepest, most protected parts of the nest wood. The emergence of new workers is a constant and rewarding sight in a well-cared-for colony.

Nuptial flights occur during the summer, usually between June and August, on warm, humid days. Interestingly, their flights often happen earlier in the day than those of L. niger. After mating, the queen searches for a suitable crevice in a tree or a piece of rotted wood to start her new colony. She is a claustral founder, meaning she doesn't eat until her first workers are ready to forage for her. In captivity, these queens require a very stable and humid environment to succeed.

Environmental Requirements

To keep Lasius brunneus healthy, you should simulate their humid, wood-based environment. They require a moderate temperature gradient in the nest, with a warm area around 22-24°C (72-75°F). They do not like excessive heat. Humidity is very important; the nest should be kept quite moist (60-70% humidity) to mimic the conditions inside a living tree. They are sensitive to vibrations, so the habitat should be placed in a quiet location.

Hibernation is a vital requirement for this temperate species. From November to March, the colony should be kept in a cool area (around 5-10°C). This period of diapause is essential for the long-term health of the queen and ensures she will continue her egg-laying cycle in the spring. During hibernation, they require very little care, only needing occasional checks for moisture.

Keeping Lasius brunneus as Pets

Lasius brunneus is a "connoisseur's ant" for those who love the genus Lasius but want something a bit more specialized and beautiful. Their bicolored appearance and arboreal lifestyle make them a unique addition to any collection. While they can be shy, their complex social structure and their relationship with wood-based habitats provide endless fascination. They are hardy and long-lived, offering a peaceful and rewarding ant-keeping experience.

Recommended Habitats

For an arboreal and wood-loving species like the Brown Tree Ant, we recommend the following ANT SHACK habitats:

• All-in-One Desktop Ant Habitat - This is a perfect starter home for L. brunneus. The secure acrylic nest retains the necessary moisture, and the integrated outworld is easy to furnish with pieces of bark and wood to make them feel at home.
• Natural Ant Habitat Kit - Large - This kit allows you to create a beautiful forest-like environment. By using a mix of soil and vertical pieces of wood, you can provide a naturalistic habitat that encourages their climbing and wood-nesting behaviors.
• Ant Habitat “Paris“ - For larger colonies, the "Paris" model's horizontal layout provides plenty of room for workers to organize their brood and for foragers to explore. Its high-quality design makes for excellent viewing of their beautiful bicoloration.