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Communication between members of Atta sexdens involves a combination of chemicals called pheremones secreted from various glands, and touch. The gaster, the organ used for applying these chemicals, can be used to mark cut leaves, cutting sites, territory boundaries, and paths to take to get to cutting sites or rubbish heaps. If the ground is already marked, the ant will not mark it again unless the scent has faded.
Atta ants also can communicate by using a file-and-scraper mechanism that produces sound both in the air and through the ground. This mechanism is usually used to recruit workers to a particular patch of good vegetation.
Communication Channels: tactile ; acoustic ; chemical
Other Communication Modes: pheromones ; scent marks ; vibrations
Perception Channels: visual ; tactile ; acoustic ; vibrations ; chemical
Atta sexdens is not listed in the IUCN Red List, CITIES appendices, or the United States Endangered Species Act.
US Federal List: no special status
CITES: no special status
Ants in general progress through four stages of development: egg, larva, pupa, and adult. Atta sexdens, like all hymenopterans are haplo-diploid, meaning males are haploid (one of each chromosome) and females are diploid (a pair of each chromosome). Sex is determined by the type of egg is laid. Unfertilized eggs will turn out to be males, which are strictly used for mating and are short-lived. Fertilized eggs produce females.
Three to four weeks after being layed, the egg hatches and a larva emerges. In Atta ants, the larvae are fed by secretions from gardener-nurse ants and trophic eggs (unfertilized eggs that are used as food). The larvae, after an additional 3-4 weeks, spin cocoons around themselves and pupate. After 3-4 more weeks, the pupae hatch into adult workers, ready to serve the queen and colony.
Development - Life Cycle: metamorphosis
Usually when Atta ants cross human paths, the ants are not looked upon favorably. Atta sexdens and Atta cephalotes are the principal insect pests where they are found, destroying billions of dollars worth of crops with their ability to quickly defoliate and strip crops of anything useful to the ants. In fact, Atta ants are considered the number one herbivorous pest in many areas where they are found.
Negative Impacts: crop pest
Humans in some areas of Mexico eat these ants as a source of protein.
Positive Impacts: food
The movement of leaves and waste and the construction of new canals by colonies of A. sexdens contribute a great deal to their ecosystem. By constructing and expanding the colony, A. sexdens colonies aerate and turn over almost 40,000 kg of soil before they finish.
Atta ants also redistribute vital elements into the soil through processing and removal of waste products from the colony.
Atta ants also have a mutualistic relationship with their fungal crops. The fungus provides different types of nutrition to the ants, and the ants feed the fungus and protect it from parasitic fungi (genus Escovopsis). The ants use a bacteria (genus Streptomyces) that produces antibodies to fight Escovopsis. The parasite, if left unchecked, will easily destroy the entire fungus crop, severely hampering the colony's ability to survive. Many ants, at the first sign of the infection, will abandon the crop and try to get the uninfected crop elsewhere in the colony.
Ecosystem Impact: soil aeration
Mutualist Species:
Colonies of A. sexdens, like all leaf cutter ants, are mycophagic (fungus-eaters). The ants cut fresh leaves up into small pieces to use as a substrate for their fungus crop (flower petels are often used for the same purpose). Once the leaf fragments are inside the nest each is prepared with a drop of anal liquid which acts as a fertilizer. Once the leaf is placed into position a small amount of fungus is placed onto the anal drop. In addition to leaves, flower petels are often used for the same purpose. In addition to cultivating the fungus, Atta ants feed on plant sap.
Other Foods: fungus
Primary Diet: herbivore (Eats sap or other plant foods); mycophage
Atta sexdens can be found throughout Central and South America from as far north as Texas down to Southern Argentina.
Biogeographic Regions: nearctic (Native ); neotropical (Native )
Colonies of Atta sexdens are found scattered throughout forest floors and fields - anywhere with an appropriate climate and abundant foliage to harvest. Rather than building upward, A. sexdens colonies will dig a nest 2-6 meters (6-18 feet) deep into the ground.
Habitat Regions: tropical ; terrestrial
Terrestrial Biomes: forest ; rainforest ; scrub forest
Other Habitat Features: agricultural
Colonies of Atta sexdens have a success rate of approximately 2.5%, that is, only 2.5% of queens sent out to build new colonies actually succeed in doing so.
Those colonies that do survive, as a whole, live about as long as their queens do, which is 10-15 years. By this time, the original colony has likely sent out several mating flights' worth of queens to populate other areas and propagate their genes.
Typical lifespan
Status: wild: 10 to 15 years.
Atta sexdens divides its colony members into four major castes, each differentiated by a range of head widths.
Gardener-Nurses: The smallest of the four castes, gardener-nurses have an average head width of 1.0 mm, and range from 0.6 mm to 1.2 mm.
Within-nest Generalists: The next size up, they have an average head width of 1.4 mm, and range from 1.2 mm to 1.6 mm.
Foragers-Excavators: The second-largest caste, their heads average 2.2 mm, and range from 1.6 mm to 2.4 mm, with a few individuals above 2.4 mm.
Defenders: The largest of the ant castes, defenders usually have a head width above 3.0 mm.
The queen is the largest ant in the colony, often measuring an inch or longer.
Average mass: .02 g.
Range length: 3 to 24 mm.
Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry ; polymorphic ; venomous
Sexual Dimorphism: sexes shaped differently
Like many other kinds of ants, Atta sexdens has a specialized caste devoted to fending off predators that disturb the nest. Usually, strength (and victory) depends on the number of defender-caste (called soldiers) ants that can arrive on the scene and attack the predator. Soldier ants are the largest in the colony and have evolved very sharp mandibles for use in defense of the nest or its workers. Depending on the size of the predator, smaller or larger ants will be dispatched to fend off the attack.
Known Predators:
Although no one has yet observed the complete Atta sexdens mating process, it is theorized that A. sexdens queens are polyandrous. When the queen goes on her mating flight, called the revoada, she needs to obtain enough sperm to last her entire lifespan. Mated queens may contain more that 300 million sperm when all the mating is done. No one male is likely able to produce enough sperm, so it is likely that the female mates with three to eight individuals during her revoada.
Only queens and males are sexually active and able to mate. All other castes are sterile.
Mating System: polyandrous ; eusocial
Queens of Atta sexdens are the only females that mate. Mating usually occurs from late October through the middle of december. After gaining enough sperm to found a new colony, the queen will fly away from her old colony, up to approximately 11 km, shed her wings, burrow into the ground, and begin egg-laying.
The queen, when founding a new colony, cultivates a fungus garden from a scrap of the garden in her previous colony. Rather than eat the fungus, she lives on her own fat reserves, eggs, and her wing muscles (which she won't need anymore). The first batch of eggs, cared for by the queen, hatch worker ants of the gardener caste. After there are enough gardener-nurses to take care of both brood and fungus, the queen becomes strictly an egg-laying machine for the rest of her life. Queens may produce up to 150 million daughters during their lifetime. The next batches of eggs are the specialists and forager-excavators, to help expand the colony and find more material for the fungus to grow on. From this point, all four castes of ants may appear in the queen's eggs.
Atta sexdens queens determine what amount of what worker castes to produce depending on the size of the colony and the age of the queen. Wilson and Holdobler (1994) experimented with a mature colony, reducing its size in proportion to give it the appearance of a young colony. Instead of going by age and producing large workers and soldiers, the queen reverted to producing small and mid-size workers as if she were in command of a younger colony.
Breeding interval: Queens and males breed only during one mating season of their lives. Non-queen females cannot breed.
Breeding season: End of October to Middle of December
Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (Internal ); oviparous ; sperm-storing ; delayed fertilization
The eggs, larvae, and pupae of Atta sexdens are generally cared for by gardener-nurse caste workers, with some help from the within-nest specialists if the larvae or pupae are extremely large. The one exception to this rule is the first few clutches of eggs laid by a founding queen, as she has no workers to take care of the larvae and must take care of them herself.
These nurses feed the larvae with trophic eggs and fungus, sometimes by regurgitation. They also protect, manipulate and groom the eggs, larvae, and pupae, assisting them through their metamorphosis by licking off the last vestiges of a previous stage.
Parental Investment: female parental care
