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Negotiated geographies: human–animal interactions in South America

Leafcutter ants

Dr Diogo de Carvalho Cabral, an environmental historical geographer at the Institute of Latin American Studies, describes a recent research project, funded by the British Academy’s Newton International Fellowship scheme, that explores leaf-cutting ant agency and 19th-century state-building.

‘Leafcutter ants are neotropical-endemic social insects that feed on underground fungus gardens produced with plant material harvested from wild and cultivated species. Human-led deforestation benefits leafcutters in three major ways.

‘First, by eliminating tree canopies, it creates sunnier, drier, litter-free environments that most leafcutter species enjoy. Second, by destroying the habitats of their predators, especially birds, anteaters, lizards and frogs, it allows leafcutters to lead a much less precarious life. Third, by introducing environmental boundaries into a previously continuous landscape, it permits the ants to enjoy access to a wider range of habitat.

‘Whether facing roads, crops, pastures, dwellings or other facilities, the trees at the border of newly formed forest remnants experience harsher regimes of sunlight, temperature and wind, as well as new interactions with the fauna. Over time such ‘edge effects’ lead to the replacement of mature forest species — emergent trees bearing larger seeds or fleshier fruits, with supra-annual flowering and pollinated by specialised biotic vectors — with pioneer bushes and grasses that are especially alluring to leafcutters. The ants are also generally fond of defoliating the crops that humans grow on slashed-and-burned tracts. In 19th-century Brazil several such cultivated species were domesticated versions of wild pioneers, such as sugarcane and cassava.

‘Pioneer landholdings were quite literally clearings opened amidst dense forest. As more people came in, the clearings multiplied, always accompanied by side roads. Thus, a previously continuous forest area gradually shrunk into increasingly smaller and isolated remnant patches.

‘As the settlement matured and forest cover became scarcer, people tended to preserve the remaining stocks on marginal lands, setting them aside as timber and fuelwood providers. In rural small-holding communities and urban fringes such forest reserves typically bordered modest crops, orchards and gardens, forming land mosaics that leafcutters fully exploited, unencumbered by any sense of respect for property boundaries. Even in municipal seats, urban land properties often had large backyards, sometimes occupying the full width of the block, with their gardens and orchards constantly being harassed by ants based in neighbouring properties.

‘Responsive to changing resource availability, the trunk trails through which worker ants transport plant material sometimes extend more than 250 metres away from the nest, covering areas often as large as 20 hectares. Such a reach would allow worker ants to forage in two or three different landholdings with their nest, however, firmly located in just one of them.

‘By transgressing property boundaries, leafcutters helped to shape modern notions of public authority and service. Complaints about leafcutters based at neighbouring properties are common in the meeting minutes of São Paulo’s city council in the 1830s. The farmers could leave an ant nest at the edge of their estates in peace, if it disturbed their neighbour’s garden only.

‘In 1806, in Mariana, Minas Gerais, an innkeeper filed for the destruction of a nest located on the neighbouring property, whose worker ants had been attacking her orchard. The neighbour in question was unwilling to cooperate, perhaps to hurt the claimant’s business.

‘Records of supposed bad faith also exist for the end of the century in São José dos Campos, in the Paraíba Valley. Among the ant-related complaints in a local newspaper in the 1880s, one addressed to municipal councilmen and signed by “the neighbours victimised by the ants”, read: “Existing in the pasture of Mr Bino Miguel […] several anthills; and the said gentleman, aiming to do evil to his neighbours, refuses to kill them, even grumbling when the inspector gives correction in his dominions; we ask the council members to make that gentleman understand that the law applies to all.”

‘Sometimes, however, simple neglect was the cause of anguish. In March 1864, residents at Engenho Novo, a semi-rural suburb of Rio de Janeiro, complained in the Jornal do Commercio that “the great ant nests” located on some deceased people’s properties were making nearby orchards and plantations “disappear overnight”, and called for parish inspectors to “use their authority to put an end to such a scourge”.

‘Thus, instead of passively conducing to human-built, neatly controlled environments, forest clearing in 19th-century Brazil prompted rescaled patterns of native defoliation, which in turn posed new challenges to human political communities. Responding to circumstances triggered by human deforestation, leafcutters expanded their populations, thereby changing the conditions of cohabitation. Their enhanced herbivory gave rise to damage and conflicts within the human communities, which in turn called for public actions. New practices were implemented, most notably the municipal inspectors’  legal duties concerning the surveying of ant nests within both common areas and private properties – a development with the potential to reverberate on the local circuits of political power.’

Dr Diogo de Carvalho Cabral is interested in the relations between native ecosystems, especially forest and savannah, and modern Brazilian society. He studies the role of literacy in the 16th-century Portuguese colonisation of Brazilian Atlantic forests, landscape change and the geography of agricultural production in the late 20th century.

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