Leafcutter Ant (Atta cephalotes) Fact Sheet: Behavior & Ecology

Mixed observations

• Colonies may be active during the day and at night (e.g., Wetterer 1994; Rao 2000; Bustamante et al. 2020)
• Some colonies primarily diurnal (e.g., Wetterer 1994)
• Nocturnal in some locations (e.g., Cherrett 1968; Linksvayer et al. 2002)
• Avoid daytime parasitic flies (Orr 1992; Rao 2000; Yackulic and Lewis 2007)
• Foraging activity limited during rainstorms (Weber 1972b; Lewis et al. 1974; Farji-Brener et al. 2018)
• Drop leaves and move out of the rain (Hodgson 1955, observing Atta colombica)
• Return to nest, or shelter under tree branches or roots

Influence of temperature

• Activity increases with warmer air and soil temperatures (Bustamante et al. 2020)
• Better able to run and gain energy at warmer temperatures (reported for Atta columbica) (Hurlbert et al. 2008)
• Seek shade when direct sun too hot (Bustamante et al. 2020)
• Return to dropped leaf fragments on trail when cooler
• Avoid activity at hottest times of day, in some locations (Belt 1874; Cherrett 1968)
• Can forage at surface temperatures between 17 and 45°C (63 and 113°F) (Bustamante and Amarillo-Suárez 2019; Bustamante et al. 2020)
• Reduced activity above surface temperatures of 45°C (113°F)

Structure

• Huge nest structures that house millions of workers and immature ants (Brent 1886; Stahel and Geijskes 1939 cited by Hölldobler and Wilson 1990; Stahel 1943; Hölldobler and Wilson 2009; Hölldobler and Wilson 2011)
  • Above ground, appear as soil mounds
    • Also see Weber (1972b)
  • Below ground, intricate network of tunnels and hundreds of fungal chambers, plus refuse chambers
    • Interconnected (but distributed) architecture
    • Network expands over time
    • Highest concentration of fungal garden chambers near nest center
  • Numerous entrances
    • Provides access points and ventilation
• Larvae develop in wooly, sponge-like fungus garden structure (Brent 1886; Weber 1972b; Quinlan and Cherrett 1979)
  • Held together by fungal threads (Stahel 1943)
• Measurements
  • For Atta spp., nest can extend 3-6 m (10-20 ft) below ground (Stahel and Geijskes 1939 cited by Hölldobler and Wilson 1990; Stahel 1943; Hölldobler and Wilson 1990; Fernández et al. 2015) 

Nest maintenance activities

• Waste and undecomposed material removed from fungal gardens and stored in separate, underground refuse chambers (Stahel 1943; Hart and Ratnieks 2001; Hölldobler and Wilson 2009; Hölldobler and Wilson 2011; Swanson et al. 2019)
  • Helps prevent spread of pathogens
    • Below ground storage may speed up decomposition
    • Tunnels may be closed off with soil
  • Mainly performed by older workers
• Clear plants (seedlings) from around nest (Brent 1886; Garrettson et al. 1998; Meyer et al. 2011a; Stephan et al. 2015)
  • Leave soil surface bare
• Build ventilation passages to the surface (Belt 1874; Stahel and Geijskes 1939 cited by Hölldobler and Wilson 1990; Hölldobler and Wilson 1990; Swanson et al. 2019)
  • Helps them control temperature and gas composition in nest chamber
• Work to prevent flooding, ventilate nests against high carbon dioxide levels, shut down tunnels when threat, recycle nest materials (Belt 1874; Swanson et al. 2019)

Influence on forest ecology

• See "Ecosystem engineer"

Ant trails

• Travel along well-maintained foraging trails, some longer than 500 m (2,000 ft) (Urbas et al. 2007; Hölldobler and Wilson 2009; Hölldobler and Wilson 2011)
  • Function as “superhighways”
  • Well maintained, kept clear of vegetation
  • Used for months or years
• Fallen branches, logs, and exposed roots commonly part of trail and nest systems (Farji-Brener et al. 2007; Freeman and Chaves-Campos 2016)
  • Smooth surfaces speed up walking (faster than on soil or through leaf litter) (Freeman and Chaves-Campos 2016)
    • Pheromones might remain on branch longer than the ground
• Typically, an ant that cuts a leaf carries its fragment to the nest (Weber 1972a; Hölldobler and Wilson 1990; Hart and Ratnieks 2001)
  • Less commonly, leaves transferred between workers (see “Leaf transfer”) (Hubbell et al. 1980; Hart and Ratnieks 2001) or dropped to ground from trees (Hubbell et al. 1980)
• Head-to-head encounters between foragers common (Burd et al. 2002; Burd and Aranwela 2003; Farji-Brener et al. 2010)
  • Facilitates exchange of leaves and information about food (i.e., higher foraging efficiency)

Dispersal

• Atta colonies begin to produce winged queens and males after about 3 years (Hölldobler and Wilson 2009; Hölldobler and Wilson 2011)
  • Also see Courtship and Colony Founding
• Muñoz-Valencia et al. (2020) report a mixture of short- (around 1–2 km) to longer-distance migrations
• Medium-long distance migrations reported, with nuptial flights up to 9.7 km (Cherrett 1968; Helms 2018)
  • May be aided by wind
  • Carry nutrient reserves needed to found a new colony

Overview

• Colonial insect dubbed a “superorganism” (Wilson and Hölldobler 2005; Hölldobler and Wilson 2009)
  • Reproductive caste system
    • Long-lived queen and her female offspring
      • Queen is only reproductive individual in a colony
    • Males short-lived; die soon after mating
  • Sterile workers (Dijkstra and Boomsma 2006; Hölldobler and Wilson 2009; Hölldobler and Wilson 2011)
  • Overlapping generations that contribute to colony labor
  • Cooperative care of brood young
• In Atta and Acromyrmex, worker size and anatomy influences role in colony life (Hölldobler and Wilson 2009; Hölldobler and Wilson 2011)
  • See “Labor (caste) system,” below
• Complex communication and colony defense systems (Wilson and Hölldobler 2005)

Labor (caste) system

Note: Wilson (1980b) studied Atta sexdens but caste system similar across Atta species (e.g., Hölldobler and Wilson 1990; Hölldobler and Wilson 2011).

• Activities organized by assembly line (Wilson 1980a; Wilson 1983; Hölldobler and Wilson 1990; Hölldobler and Wilson 2009; Hölldobler and Wilson 2011)
  • Foragers return to nest and drop leaf fragments on nest chamber floor
  • “Processing ants” clip fragments into small pieces (about 1 to 2 mm across)
  • Gardening ants crush and mold pieces into pellets, add fecal liquid (“manure”), and insert into sponge-like fungus garden structure
    • See Diet & Feeding
    • Add loose strands of fungus to new leaf pellet surfaces
  • Other garden-tending workers patrol fungus gardens, cultivating and cleaning
• Striking differences in body size and proportions between smallest and largest workers (Wilson 1980a; Wilson 1983; Hölldobler and Wilson 2009; Hölldobler and Wilson 2011)
  • Body sizes more variable as colony develops and matures
• Small, young workers tend fungi and harvest fungi in subterranean chambers (Wilson 1980a; Hölldobler and Wilson 2009; Hölldobler and Wilson 2011)
  • Small body structures needed for handling delicate fungal structures
• Large, older workers perform tasks outside the nest (Wilson 1980a; Hölldobler and Wilson 2009; Hölldobler and Wilson 2011)
• Labor groups, named for size (Hart et al. 2002; Hölldobler and Wilson 2009; Hölldobler and Wilson 2011; caste system articles by E.O. Wilson; early observations by Belt (1874) and others)
  • Minims
    • Work underground, tending fungi, eggs, and immature ants
    • “Hitchhike” on leaves being transported back to nest and defend against parasitic flies; begin the leaf-cleaning process before reaching the nest (e.g., Brent 1886; Stahel 1943; Eibl-Eibesfeldt and Eibl-Eibesfeldt 1967; Weber 1972a; Feener and Moss 1990; Linksvayer et al. 2002; Hölldobler and Wilson 2011; Alejandro G. Farji-Brener, personal communication, 2022)
    • Clear trail and deposit trail pheromones
  • Medias
    • Harvest leaves and labor inside the nest
    • Process leaves inside the nest (Garrett et al. 2016)
  • Majors
    • Appear to exclusively perform defense and trail maintenance outside the nest
    • Also carry large forage items (e.g., fruits)
• Specialized workers, named by role (Stahel 1943; Wilson 1980b; Wilson 1980a; Stark et al. 2019)
  • Carriers: carry leaf clipping from canopy to nest
  • Riders: ride on leaf, protecting against aerial attack (parasitic flies); also clean leaf (Feener and Moss 1990; Rao 2000; Yackulic and Lewis 2007)
    • Typically minims size-age class
  • Soldiers: defend foragers on trail from terrestrial attack
• Additional roles
  • Small workers groom and protect queen (Wilson 1980a; Hölldobler and Wilson 2011)
  • Refuse workers (Bot et al. 2001; Hart and Ratnieks 2001; Hart et al. 2002; Hölldobler and Wilson 2009; Swanson et al. 2019)
    • Dispose of waste in refuse chambers
    • Segregated from rest of nest/other nestmates
      • Prevented from leaving refuse heap areas by nestmates
      • Ensures nest hygiene (prevents contamination of food source)

Olfactory communication

• Sense of smell
• Well-developed sense of smell in Atta (Hölldobler and Wilson 2011; Muratore et al. 2022)
• High numbers of pheromone-sensitive synapse clusters (glomeruli) in brain
• Complex neural connections for processing chemical signals
• Receptor nerve cells on antennae
• Pheromone composition
• Potent chemical components (Riley et al. 1974; Hölldobler and Wilson 2011)
• A tiny amount (1 mg) of one recruitment compound is theoretically sufficient to attract foragers that would follow a trail around the Earth’s circumference 3 times
• Pheromone influence on social behavior
• Used to mark foraging routes and nests (Jaffé et al. 1979; Hölldobler and Wilson 1986; Hölldobler and Wilson 2009)
• Orient workers on trails and tree branches
• Scent concentration reinforced by foragers walking on trails
• Used to recruit workers (Riley et al. 1974; Jaffe and Howse 1979; Hölldobler and Wilson 2009; Hölldobler and Wilson 2011)
• Drive trail formation and leaf harvesting in new areas
• Concentration influenced by desirability of food and number of ants already at the food source
• Appear to be cues of colony identity (Hölldobler and Wilson 1986)
• Induce marking behavior in members of other colonies, presumably to “cover up” the scent of the rival colony

Defense

• Parasitic flies (phorid flies) (e.g., Eibl-Eibesfeldt and Eibl-Eibesfeldt 1967; Wilson 1980a; Alma et al. 2019)
  • Flies attack during the day and lay an egg in the head capsule of leafcutter ants (Eibl-Eibesfeldt and Eibl-Eibesfeldt 1967; Orr 1992; Feener and Brown 1993)
    • Flies generally select larger-bodied foragers as hosts
    • More commonly attack ants leaving nest (Feener and Moss 1990; Feener and Brown 1993)
      • More difficult for flies to get into position and attack ants carrying leaves (returning to nest)
  • Ants adjust foraging behavior to avoid fly attacks (Orr 1992; Feener and Brown 1993)
    • In some locations, small workers (not suitable as fly hosts) more active during the day; larger workers active outside the nest at night
  • Small worker ants (minims) “hitchhike”/ride on leaves to deter fly attacks against foragers (Eibl-Eibesfeldt and Eibl-Eibesfeldt 1967; Wilson 1980a; Feener and Moss 1990)
    • Protection of all workers limited by need for minims to also tend brood and fungal gardens
    • Also see “Labor (caste) system”
  • Behavioral responses when attacked (Eibl-Eibesfeldt and Eibl-Eibesfeldt 1967; Feener and Moss 1990; Orr 1992; Feener and Brown 1993)
    • Retreat into nest
    • Attempt to outrun flies
    • Adopt “C posture” (stand on back 4 legs with body curved)
    • Bite (quickly open and close mandibles)
    • Try to knock flies off leaves carried
• Army ants
  • Workers attack army ant scouts (Hölldobler and Wilson 2011)
  • Barricade nest entrances with leaf fragments (Swartz 1998)

Leaf transfer

• Behavior when ants pass leaf fragments in a relay process to nest (Belt 1874; Hubbell et al. 1980; Hart et al. 2002; Kwaku et al. 2020)
• Direct transfer: one ant passes leaf to another ant
• Most common on tree trunks (vertical surfaces) (Kwaku et al. 2020)
• Indirect transfer: one ant drops leaf fragment along trail that another ant picks up (Hart and Ratnieks 2000; Hart et al. 2002)
• Most common at base of tree or on the ground (Kwaku et al. 2020)
• In certain locations, drop fragments from tree to ground (Hubbell et al. 1980; Hart et al. 2002)
• More common in some other Atta species
• Saves time and effort to climb the tree trunk

Self-grooming

• Spread secretions from metapleural gland (located above hind leg) over cuticle surface (e.g., Do Nascimento et al. 1996; Poulsen et al. 2002; Fernández-Marín et al. 2006; Yek and Mueller 2011)
• Protective function; secretions suppress growth of harmful funguses on cuticle surface through antibiotics
• Hygiene is a major function of the metapleural gland
• May also have other functions (see Yek and Mueller 2011)

A top consumer of herbaceous plants in Neotropics

• Very important role in tropical ecosystems (Wheeler 1908; Weber 1972a; Hölldobler and Wilson 1990; Hölldobler and Wilson 2009; Hölldobler and Wilson 2011; Swanson et al. 2019)
  • Harvest and process enormous amounts of plant material (Hölldobler and Wilson 2011)
  • Stimulate new plant growth (Wirth et al. 2003)
  • Facilitate nutrient cycling (Haines 1983; Perfecto and Vandermeer 1993; Wirth et al. 2003)
• Fill an ecological niche in Neotropics similar to mammal herbivores elsewhere (Hölldobler and Wilson 1990)
• Exert greater herbivory pressure along forest edges, compared to forest interiors (Urbas et al. 2007; Meyer et al. 2011b)
  • Also see “Population estimates”

Ecosystem engineer

• Leaf-cutting
  • High leaf-cutting rates on plants around nest (e.g., Cherrett 1968)
    • Some plant species benefit from higher light levels (Farji-Brener and Illes 2000; Meyer et al. 2011a; Stephan et al. 2015)
  • Create gaps in rainforest canopy through leaf harvesting behavior (e.g., Farji-Brener and Illes 2000; Corrêa et al. 2010; Meyer et al. 2011b; Corrêa et al. 2016; Swanson et al. 2019)
    • Affects sunlight levels, wind, and temperature
  • Substantial impact on plant assemblages (plant species that tend to grow together) and seedling survival near nests through leaf removal and possibly root disturbance (e.g., Corrêa et al. 2010; Meyer et al. 2011a; Silva et al. 2012)
• Fungus cultivation and decomposition
  • Move plant matter underground (Atta sp.: Farji-Brener and Silva 1995; Moutinho et al. 2003; Sternberg et al. 2007; Swanson et al. 2019)
    • Enhance nutrients available in deep soil and carbon through accumulation of leaf material, fungus-cultivation, and breakdown of plant matter in refuse dumps
  • Increased nitrogen availability due to symbiotic bacteria, which perform nitrogen fixation in fungal gardens (Pinto-Tomás et al. 2009)
    • Promotes cultivation of ants’ food source (fungus)
    • Nitrogen also high in refuse dumps, which then enters surrounding soil
  • Nests are decomposition “hot spots” (Swanson et al. 2019)
    • Produce large amounts of carbon dioxide (Fernandez-Bou et al. 2019)
      • Detectable ecological impact, though in one Costa Rican rainforest, estimated as less than 1% of total forest carbon dioxide emissions (Fernandez-Bou et al. 2019)
    • Carbon dioxide ventilated from nest openings and diffuses into the surrounding soil (Fernandez-Bou et al. 2019)
      • Ants sense carbon dioxide levels with antennae (Kleineidam and Tautz 1996)
  • Slightly higher soil temperature near nest center, compared to areas farther from nest (Meyer et al. 2011b)
• Digging and nesting behavior
  • Influence soil ecology through nesting, digging, and discarding refuse (e.g., Farji-Brener and Illes 2000; Farji-Brener and Werenkraut 2015; Fernandez-Bou et al. 2019)
    • Enhance soil density, penetrability, aeration, and turnover (Alvarado et al. 1981; Perfecto and Vandermeer 1993; Moutinho et al. 2003; Swanson et al. 2019)
  • Clear above-ground leaf litter, which reduces available soil nutrients, such as nitrogen and carbon (Meyer et al. 2013)
    • In one study, nest-building and maintenance activities caused declines in leaf-litter insects near leafcutter ant nests (Wells et al. 2017)
      • Likely impacted by ants’ removal of leaf litter (also resulting in increased light and drier soils)
      • Differences in arthropod communities add complexity to rainforest ecosystems
• After colony death
  • Plants, especially those of small sizes, more abundant and diverse at sites of abandoned nests (Garrettson et al. 1998; Farji-Brener and Illes 2000)
  • Birth and death of colonies may contribute to “a dynamic mosaic of soil microhabitats” (Perfecto and Vandermeer 1993)

Relationship with humans

• Atta species commonly considered severe pests (Belt 1874; Brent 1886; Hölldobler and Wilson 1990; Hölldobler and Wilson 2009; Hölldobler and Wilson 2011; Valencia-Giraldo et al. 2020)
• Damage agriculture, gardens, and also permeate urban areas (e.g., Montoya-Lerma et al. 2012)
• Defoliate most kinds of crops, including cocoa, coffee, and fruit trees (Belt 1874; Brent 1886; Hölldobler and Wilson 1990; Varón et al. 2011)
• Holes of subterranean nests can injure livestock and farming machinery (Hölldobler and Wilson 1990)
• Control agents range from insecticides to removal of queens to compost treatments to biological pathogens (Montoya-Lerma et al. 2012; Della Lucia et al. 2014)
• Shrub Tithonia diversifolia said to deter leafcutter ants
• Alternatives to chemical insecticides
• Control agents, such as plant- or fungus-based approaches, proposed to repel leafcutter ants or eliminate their food source (Castaño-Quintana et al. 2013; Rodriguez et al. 2015; Daza et al. 2019)

In the Atta labor system, striking differences in body size and anatomy exist between the smallest and largest workers.

Forager with hitchhiker on top of leaf fragment.

Atta leafcutter ant colonies are comparable in social complexity with honeybees.

Small, young workers tend and harvest fungi in subterranean chambers, but some also "hitchhike” on leaves to begin the leaf-cleaning process and defend leaf-carrying ants against parasitic flies.

Image credit: © San Diego Zoo Wildlife Alliance. All rights reserved.