Acromyrmex ambiguus

Acromyrmex ambiguus is a species of New World ants of the subfamily Myrmicinae found in the wild naturally in southern Brazil, Paraguay and Uruguay. Commonly known as "leaf-cutter ants", they are a species of ant from one of the two genera of advanced fungus-growing ants within the tribe Attini.^[2]

Acromyrmex can be identified from the closely related Atta genus of leafcutter ants since they have four pairs of spines and a rough exoskeleton on the upper surface of the thorax.

A mature A. ambiguus colony contains mostly sterile female workers. They are divided into castes, based mostly on size, that perform different functions. Acromyrmex exhibits a high degree of biological polymorphism, four castes being present in established colonies - minims (or "garden ants"), minors, mediae, and majors. Majors are also known as soldiers or dinergates. Each caste has a specific function within the colony. Acromyrmex ants are less polymorphic than the other genera of leafcutter ants Atta, meaning that there is comparatively less differential in size from the smallest to largest types of Acromymex. The high degree of polymorphism in this genus is also suggestive of its high degree of advancement.

Like Atta, Acromyrmex subsists mostly on a particular species of fungus (genus Leucocoprinus) which it cultivates on a medium of masticated leaf tissue. This is the sole food of the queen and other colony members that remain in the nest. The media workers also gain subsistence from plant sap they ingest whilst physically cutting out sections of leaf from a variety of plants.

Before leaving their parent colonies, winged females take a small section of fungus into their bucchal pouches and it is with this that the subsequently wingless queens 'seed' the fungus gardens of incipient colonies, cutting and collecting the first few sections of leaf themselves.

When deciding where to build a new nest A. ambiguus workers use the direction of the airflow as an environmental cue for spatially guiding their building behaviour, yet workers only responded if the humidity content of the circulating air was low. These building responses seem to result from a compromise between the need of air renewal and the avoidance of unsuitable climatic conditions.

Acromyrmex has evolved to change food plants constantly, preventing a colony from completely stripping off leaves and thereby killing trees, thus avoiding negative biological feedback on account of their sheer numbers. However, this does not diminish the huge quantities of foliage they harvest.

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