Lasius fuliginosus – Lifestyle, Nest-Building & Care in Detail

The “Jet Black Ant” as a Specialist Among Europe's Ants

Lasius fuliginosus, also known as the jet black ant, is one of the most fascinating ant species in Europe. Its extremely smooth, almost lacquer-black body, its extraordinary carton-nest construction, and its symbiotic lifestyle make it a biologically remarkable species. At the same time, due to its complex founding biology and the special demands it places on climate, food, space, and material, it is only suitable for experienced ant keepers.

The species occurs throughout Europe but prefers structurally rich mixed and deciduous forests. There, it builds complex nest systems in tree hollows, dead wood, and under bark. The combination of scientifically fascinating social biology and its unique nest means Lasius fuliginosus is valued by researchers just as much as by experienced keepers.

How Lasius fuliginosus Lives in Nature

Lasius fuliginosus belongs to the subgenus Cautolasius and is closely related to Lasius umbratus and Lasius mixtus. The species is highly polygynous, meaning it has multiple queens per colony. Under optimal conditions, colonies can contain several million workers and form multiple satellite nests.

The ants are aphidicolous, meaning they live in close association with aphids. A large portion of the carbohydrates they need comes from honeydew. In addition, they hunt small arthropods and carrion, so while they are often considered “sweet-food-oriented,” they also require a steady supply of protein.

Ecologically, the species shows a clear affinity for old trees, especially oaks, lindens, and chestnuts, which offer large cavities, decay zones, or dead heartwood. Such structures are essential for building their famous carton nests.

The Carton Nest of Lasius fuliginosus

The nest-building of Lasius fuliginosus is one of the most remarkable traits of this species and clearly distinguishes it from most other central European ants. The species is one of the few known “carton-nest ants” in Europe. It builds its nests not primarily from soil or wood, but from a carton-like material made of decomposed plant fibers bound together by fungal substances. This carton is stabilized through a unique cooperation between the ants and a specific fungus.

Fungal Symbiosis in Nest-Building

Lasius fuliginosus uses an ascomycete fungus that is closely integrated with the nest walls. The ants carry wood fibers, shredded bark pieces, and decaying plant material into the nest. These materials serve as a substrate for the fungus. The fungus then forms a dense network of hyphae that binds the fibers together, creating the characteristic carton structure.

Important to note:

The fungus does not live independently in nature — it is passed on in a colony-specific manner.

New colonies arise only through social parasitism (adoption into a host colony) and automatically take over the fungus in the process.

The carton fungus continues to grow actively and permanently stabilizes the nest.

This fungal symbiosis is functionally comparable to that of Lasius umbratus and Lasius mixtus, but in Lasius fuliginosus the carton form is especially pronounced and more firmly structured.

Nest Location

The species prefers:

• hollow trees (oak, beech, maple, old fruit trees)
  
• decaying root cavities
  
• tree crevices and dead interior wood
  
• occasionally artificial cavities (wooden posts, telephone poles)
  

The internal condition is important: the wood must not be completely rotted, but must already be somewhat decayed and offer enough microhabitats for the fungus.

Architecture and Structure

The carton nests consist of:

• multi-layered plates
  
• branching tube and tunnel structures
  
• stable “walls,” often 2–4 mm thick
  
• brood-promoting chambers with higher humidity
  

The structure resembles a mixture of a honeycomb system and paper foam.

Particularly typical:

The nest walls are often completely black, which is fitting for the common name “black wood ant.”

Humidity & Microclimate

The fungus needs a slightly humid but well-ventilated microclimate, typically:

• 60–80% humidity inside the nest
  
• constant temperatures of 20–25°C
  

The ants actively regulate this by:

• carrying moisture outward
  
• changing airflow through tunnels
  
• removing or bringing in new material
  

The colony can significantly expand its nest size – in old tree hollows, nests with a volume of several liters can easily form.

Biological Peculiarities of Nest-Building

The following key traits are scientifically documented:

• The fungal hyphae are tended by workers, similar to how leafcutter ants tend their fungus.
  
• The carton surfaces have antimicrobial properties, likely due to the fungus or enzyme-storing glandular secretions of the ants.
  
• The nest structure is extremely long-lasting – carton nests can persist for 10+ years.
  

The stability is so high that even abandoned nests remain intact for a long time.