Lasius platythorax (The Forest Black Ant)

Introduction

Lasius platythorax, commonly known as the Forest Black Ant, is a robust and fascinating relative of the ubiquitous garden ant (Lasius niger). While it may look similar to its urban cousin at a glance, Lasius platythorax has adapted specifically for life in the heart of the forest. It is a tougher, more resilient species that thrives in the decaying wood and humid leaf litter of old-growth woodlands. Known for its ability to nest in a wide variety of forest substrates, from rotten logs to the thick bark of living trees, it is a key player in the forest ecosystem.

For ant keepers, Lasius platythorax offers a "premium" experience within the genus Lasius. They are generally slightly larger and more robust than L. niger, with a more matte, sophisticated appearance. They are also less skittish and more "courageous" when it comes to defending their territory. Keeping a colony of Forest Black Ants allows you to bring a piece of the deep, humid woodland into your home, providing a window into the life of a species that has mastered the art of forest survival.

Taxonomy and Distribution

Lasius platythorax belongs to the subfamily Formicinae and the subgenus Lasius (sensu stricto). For many years, it was confused with Lasius niger due to their similar appearance. However, in the late 20th century, it was definitively separated as a distinct species based on subtle morphological differences—such as the number of hairs on its legs and thorax—and its very different habitat preferences. Its name "platythorax" (from the Greek for "flat thorax") refers to its slightly more robust and flattened thoracic structure compared to its relatives.

Their distribution covers most of Europe and Northern Asia, following the extent of the temperate forest belt. Unlike Lasius niger, which prefers open, sunny, and disturbed areas like gardens and pavements, L. platythorax is almost exclusively found in forests, bogs, and shaded woodlands. They are particularly fond of moist environments and are often the dominant ant species in ancient woodlands where dead wood is abundant.

Physical Characteristics

Lasius platythorax is a monomorphic species, with workers typically measuring between 3.5mm and 5mm. The queen is significantly larger and very robust, usually around 8-10mm. Their coloration is a deep, dark brown or jet black. One of the subtle but beautiful features of this species is its matte finish; while L. niger can appear slightly glossy, L. platythorax has a more velvety look due to its denser pubescence.

Their bodies are built for life in complex, three-dimensional environments. They have strong legs for climbing and powerful mandibles for excavating through rotted wood and soil. They possess a "formic acid" gland at the tip of their gaster, which they use both as a defensive spray and as a chemical weapon when hunting. Their antennae are highly sensitive, allowing them to navigate the dark, intricate tunnels of their forest nests.

Colony Behavior and Social Structure

Colonies of Lasius platythorax are strictly monogynous (one queen) and can grow to include several thousand workers. They are highly organized and maintain very clean nests. Socially, they are quite cooperative, with a clear division of labor that shifts as workers age. Younger workers stay deep in the nest to tend to the queen and the brood, while older workers take on the roles of foragers, scouts, and defenders.

They are less aggressive toward other ants than some species but are very defensive of their immediate nest area. One of their most interesting forest behaviors is their relationship with aphids. Like many Lasius, they "farm" aphids for honeydew, but L. platythorax is known to be particularly specialized in tending to bark-dwelling and root-dwelling aphids. In captivity, they are active and inquisitive, constantly exploring their outworld and meticulously grooming one another in the nest.

Diet and Foraging

Lasius platythorax is a generalist omnivore with a high demand for both carbohydrates and protein. Carbohydrates are the primary energy source for the workers and are obtained from honeydew and nectar. 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.

Protein is critical for the growth of the larvae and the queen's egg production. They are opportunistic scavengers and will accept a wide variety of small feeder insects, such as fruit flies, small crickets, and mealworms. Because they are forest ants, they are well-adapted to finding food in leaf litter, so they enjoy exploring a naturalistic outworld for hidden treats. A varied diet of protein and sugar will ensure a rapidly growing and healthy colony.

Life Cycle and Reproduction

The development from egg to adult worker in Lasius platythorax takes about 6 to 9 weeks, depending on the temperature. Like all Formicinae, they pupate within silk cocoons, which are often mistakenly called "ant eggs" by the public. The workers are very protective of the cocoons, often stacking them in the warmest, driest parts of the nest to ensure they develop properly.

Nuptial flights occur during the summer, usually between July and August, on warm, humid afternoons. Thousands of winged queens and males take to the air. After mating, the queen searches for a suitable nesting site—often in a rotted log or under a piece of bark—to start her new colony. She is a claustral founder, meaning she does not eat until her first workers are ready to forage for her. In captivity, these queens are very hardy and make excellent subjects for starting a colony from scratch.

Environmental Requirements

To keep Lasius platythorax healthy, you should simulate the humid forest environment. They require a temperature gradient in the nest, with a warm area around 22-24°C (72-75°F). Unlike some heat-loving species, they prefer more moderate temperatures. Humidity is very important; the nest should be kept quite moist (60-70% humidity) to mimic the conditions of a damp forest floor or a rotting log.

Hibernation is a vital requirement for this 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 to lay eggs in the following spring. During hibernation, they require very little food but should always have access to water.

Keeping Lasius platythorax as Pets

Lasius platythorax is an excellent "step up" for keepers who have successfully kept Lasius niger or Lasius flavus. They are more robust, have a beautiful matte finish, and exhibit fascinating forest-adapted behaviors. They are hardy, easy to feed, and their colonies grow at a rewarding pace. For any keeper who loves the atmosphere of the forest, the Forest Black Ant is the perfect species to bring a little bit of that woodland magic into the home.

Recommended Habitats

For a forest-dwelling species that loves humidity and wood, we recommend the following ANT SHACK habitats:

• All-in-One Desktop Ant Habitat - This is a perfect starter home for L. platythorax. The secure acrylic nest retains moisture well, and the integrated outworld makes it easy to provide the varied diet they need.
• Natural Ant Habitat Kit - Large - This kit allows you to create a beautiful forest floor setup. By using a mix of soil, bark, and moss, you can provide a naturalistic environment that these ants will thrive in.
• 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 these matte-black beauties.