Acromyrmex

Distinguished from the related genus Atta by four pairs of thoracic spines versus three pairs in Atta, and by a rough rather than smooth thoracic exoskeleton. The two-segmented petiole (two nodes) separates Acromyrmex from most other Myrmicinae. Workers show less polymorphism than Atta workers, with smaller size range between castes. Species-level identification requires examination of spine configuration, body sculpture, and geographic distribution.

Medium to large ants with dark red coloration. Body divided into head, thorax, and abdomen with a two-segmented petiole (two nodes). Thorax bears four pairs of spines on the dorsal surface, used for maneuvering leaf fragments. Exoskeleton rough in texture. Head dominated by large mandible-closing muscles. Antennae elbowed and retractable. Eyes compound but vision poor; ocelli present in queens. Queens possess wings during mating period; workers wingless.

Subterranean nests in tropical and subtropical forests, grasslands, and agricultural areas. Nests include sophisticated ventilation shafts for gas exchange and temperature regulation. Found in undisturbed natural vegetation as well as cultivated landscapes including vineyards, eucalyptus plantations, and crop fields.

Neotropical: South America, Central America, Mexico, and Caribbean Islands. Records from Colombia and throughout the range from southern South America northward through Mesoamerica.

Active year-round in tropical habitats. In subtropical areas with seasonal rainfall, foraging activity correlates with moist seasons. Nuptial flights (revoada) occur seasonally, with timing varying by species and latitude.

Obligate fungus-farmers. Cultivate symbiotic Leucoagaricus gongylophorus fungi on substrate of masticated leaf tissue. Fungal gongylidia serve as sole food for queen and nest-bound colony members. Workers additionally consume plant sap from cut leaves during foraging. Larvae fed cultivated fungus.

• Leucoagaricus gongylophorus - mutualistCultivated fungal symbiont; primary food source
• Pseudonocardia - mutualistActinobacterium living in metapleural glands; produces antibiotics against Escovopsis
• Escovopsis - parasiteNecrotrophic parasite of fungal gardens; controlled by ant-associated bacteria
• Eucalyptus urograndis - hostCommercial eucalyptus hybrid; significant damage from leaf-cutting
• Vitis vinifera - hostGrapevine; pest in Mendoza vineyards though not preferred over native vegetation
• Zea mays - hostCorn; harvested for kernels in Argentina

Holometabolous development. Colonies founded by single inseminated queen after nuptial flight; queen carries fungal inoculum in infrabuccal pouch. Incipient colonies have low survival rate (approximately 2.5%). Mature colonies monogynous (single queen) with populations reaching several hundred thousand to over 8 million individuals. Workers emerge in four castes based on size: minims (garden ants), minors, mediae, and majors (soldiers/dinergates). Workers mature to foraging age after approximately one week.

Foragers cut leaf sections with mandibles and transport them to nest in processions following pheromone trails. Trail fidelity strengthened by multiple workers depositing pheromones. Workers exhibit hygienic behaviors including self-grooming, allo-grooming, fungus weeding to remove pathogens, and waste removal to refuse dumps. Older workers serve as waste transporters. Trophallaxis used to distribute liquid food from foragers to nestmates; over 62% of replete foragers pass food via trophallaxis. Colonies switch food plants constantly to avoid depleting single resources. Aggressive defense of colony; alarm pheromones trigger colony-wide defensive response.

Major herbivores and ecosystem engineers in Neotropical forests. Process vast quantities of plant material (large colonies may remove >500 dry weight pounds of vegetation annually), contributing to nutrient cycling and soil enrichment. Fungal cultivation represents one of only three independent origins of agriculture in animals (along with ambrosia beetles and termites). Waste management and antibiotic production by associated bacteria demonstrate complex disease management in social insects.

Significant agricultural pests throughout range, defoliating crops and damaging infrastructure with nest construction. Notable pests of corn, eucalyptus, and vineyards in South America. Acromyrmex octospinosus introduced to Caribbean islands (Guadeloupe) where it causes substantial damage. Control methods include nest refuse as deterrent and biological control research using entomopathogens. Source of novel antimicrobial compounds from associated actinobacteria with potential pharmaceutical applications.

• AttaOther genus of advanced attine leafcutter ants; distinguished by three pairs of thoracic spines, smooth exoskeleton, and greater worker polymorphism
• CyphomyrmexLower attine fungus-growers; do not cut leaves but collect other plant material and insect frass for fungal cultivation
• TrachymyrmexLower attine fungus-growers with simpler fungal cultivation and smaller colony sizes

• leafcutter ants
• fungus-growing ants
• attine ants
• agricultural pests
• mutualism
• Neotropical
• social insects
• biomineral armor
• ant-fungus mutualism
• biological control target

• BugGuide
• Wikipedia
• GBIF taxonomy match
• iNaturalist taxon
• NCBI Taxonomy
• Catalogue of Life
• The Phil Ward Ant Lab: They Provided the 'Antswers' | Bug Squad
• Ants and Science Are Her Passions | Bug Squad
• Rainforest Ants 1 - Tropical fungus farmers: Leafcutter ants, Atta and Acromyrmex spp. — Bug of the Week
• Why Fungus-Farming Ants Could Be a Source for New Antimicrobial Compounds
• Formicidae | Beetles In The Bush | Page 2
• How Ants Do Battle: Toxic Sprays, Thick Armor, Overwhelming Numbers, and More
• Selected isolates of endophytic Trichoderma decrease cutting by Acromyrmex subterraneus subterraneus
• Hygienic Behavior, Liquid-Foraging, and Trophallaxis in the Leaf-Cutting Ants,Acromyrmex subterraneusand Acromyrmexoctospinosus
• PART I DISTRIBUTION, HABITS, AND NORMAL CASTES OF ACROMYRMEX
• Dieta de Acromyrmex lobicornis (Hymenoptera: Formicidae) en un viñedo orgánico de Mendoza, Argentina Diet of Acromyrmex lobicornis (Hymenoptera: Formicidae) in an organic vineyard at the Monte desert in Mendoza, Argentina
• Hongos asociados con dos poblaciones de Acromyrmex lobicornis (Formicidae) de San Luis, Argentina Fungi associated with two populations of Acromyrmex lobicornis (Formicidae) from San Luis, Argentina
• Queens of the inquiline social parasite Acromyrmex insinuator can join nest-founding queens of its host, the leaf-cutting ant Acromyrmex echinatior
• Proteome-Wide Analysis and Surface Protein Isolation for Secretome Characterization Reveal Insights into the Biology of the Leaf-Cutter Ant Acromyrmex echinatior
• Proteome-Wide Analysis and Surface Protein Isolation for Secretome Characterization Reveal Insights into the Biology of the Leaf-Cutter Ant Acromyrmex echinatior
• Comparative reproductive biology of the social parasite Acromyrmex ameliae de Souza, Soares & Della Lucia and of its host Acromyrmex subterraneus subterraneus Forel (Hymenoptera: Formicidae)