Lasius fuliginosus – Lifestyle, Nest Building & Husbandry in Detail

The "Jet Black Ant" as a Specialist Among European Ants

Lasius fuliginosus, also known as the jet black ant, is one of Europe's most fascinating ant species. Its extremely smooth, almost jet-black body, its extraordinary nest constructions made of carton nests, and its symbiotic lifestyle make it a biologically exceptional species. At the same time, due to its complex founding biology and specific requirements for 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 cavities, deadwood, and under bark. The combination of scientifically exciting social biology and its unique nest means that Lasius fuliginosus is valued by researchers 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 comprise several million workers and form multiple satellite nests.

The ants are aphidicolous, meaning they live in close association with aphids. A large part 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 proteins on an ongoing basis.

Ecologically, the species shows a clear connection to 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 features 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 earth or wood material, but from a carton-structure material consisting of decomposed plant fibers and fungus-glued substances. This carton is stabilized by a unique cooperation between the ants and a specific fungus.

Fungal Symbiosis in Nest Building

Lasius fuliginosus utilizes an ascomycete fungus that is closely associated with the nest walls. The ants carry wood fibers, shredded bark pieces, and rotting 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, thus creating the characteristic carton structure.

Important:

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

New colonies only arise through social parasitism (adoption into a host colony) and automatically acquire the fungus.

The carton fungus actively continues to grow 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 particularly pronounced and more firmly structured.

Nest Location

The species prefers:

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

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

Architecture and Structure

The carton nests consist of:

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

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

Particularly typical:

The nest walls are often completely black, which lives up to the popular name "jet black carpenter ant."

Humidity & Microclimate

The fungus requires a slightly damp, but well-ventilated microclimate, usually:

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

The ants actively regulate this by:

• carrying moisture outwards
  
• changing air currents via tunnels
  
• removing or adding material
  

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

Biological Peculiarities of Nest Building

Scientifically proven key characteristics include:

• The fungal hyphae are cared for by workers, similar to how leafcutter ants cultivate their fungus.
  
• The carton surfaces possess antimicrobial properties, likely due to the fungus or enzyme-storing glandular secretions of the ants.
  
• The nest structure is extremely durable – carton nests can last 10+ years.
  

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