|Above and below, Leafcutter ants.
All Photos: Dong Lin
ANTS: HIDDEN WORLDS REVEALED
EXHIBIT CLOSED MAY 8, 2005
Curated by Academy entomologist Brian Fisher, this exciting exhibit will showcase six colonies of live ants, each of which will display distinctive nest building and food collecting behaviors. Four of the species represented – Harvester ants, Carpenter ants, Honeypot ants, and invasive Argentine ants – are commonly found in California. The other two species, however, come from further afield. Leaf Cutter ants, which cultivate gardens of fungus in order to ensure a steady food supply, make their home in the tropical rainforests of South America, while meat eating Army ants migrate through parts of Africa and the Americas in search of prey.
The ANTS exhibit will also teach visitors about the highly complex social structures of the various ant colonies. At the Harvester ant display, visitors will be able to discern the detailed division of labor within the colony: some worker ants husk, clean and crack seeds, while others chew kernels into a soft pulp called "ant bread." Still others store sun-dried seeds in large nest chambers or apply a chemical germicide to prevent seeds from sprouting. The Honeypot ants display yet another specialized behavior — some individuals are designated as living refrigerators that are responsible for storing excess food in their stomachs. These "honey pots" hang from the ceilings of cool nest cavities, holding fast by their claws until their precious stores are required. As the desert's food supply dwindles seasonally, nest mates will stroke the antennae of a storage ant, causing it to regurgitate some of the "honey" into the supplicant's mouth.
In addition to the live ant colonies, ANTS will also feature cutting edge research by Academy scientists, including Dr. Brian Fisher's work in Madagascar. In the past few years, Fisher has discovered over 600 new species of ants in Madagascar, including the Madagascar Dracula Ant — a find that will help scientists to understand the evolution of ants from wasps. Named because of their grisly feeding habits, during which they cut holes into their own larvae to extract colorless insect blood, Dracula Ants have wasp-like abdomens and stinging behaviors.
The exhibit will also feature Academy research that is occurring closer to home, including the Bay Area Ant Survey, which will give visitors the opportunity to contribute to an ongoing Academy research project. Almost nothing is currently known about the species diversity or distribution of ants in the San Francisco area, so the Academy is embarking on an effort to create a detailed ant map for ten Bay Area counties. Visitors who wish to participate can pick up an ant collecting kit from the Academy's Naturalist Center (located on the second floor of the Howard Street facility). After collecting specimens and returning them to the Academy along with geographic data, each participant's results will be added to the project map and Web site, which will be available online at www.antweb.org.
Distribution: In the United States, Argentine ants are found primarily in the south-eastern states and in California , mostly in urban and suburban areas, and in irrigated farming areas.
Habitat: These ants prefer temperate areas with year-round moisture. They live under rocks, pavement, logs, and refuse or in cracks in the soil.
Appearance: Small worker ants are dark brown and about 1/8' long. Males are shiny, brownish black, and somewhat larger, with wings. Queens are large and brown with darker abdomens — they may possess wings or wing pods.
Diet: Argentine ants are omnivorous. Approximately 70% of their food comes from honeydew producers, such as aphids and scale insects, which are "farmed" and protected by the ants. Here at the Academy, we feed the ants live crickets, water, honey, agar, vitamins, salt and eggs.
Reproduction & Development: In the United States , this species has the unusual strategy of reproducing by "budding." In their natural range, males and females from many different colonies fly to find one another and mate. This strategy encourages genetic diversity. However, in the United States , a single colony produces many queens that lose their wings upon hatching. Some remain unmated and simply function as workers, but others are fertilized by males within the colony and ultimately start a new colony that is genetically similar to the original.
Longevity: Males live a few weeks, workers from 6-9 months, and queens up to 7 years.
Other: In California, Argentine ants are considered an extremely serious pest. It is thought that the initial colonies arrived in Louisiana in the 1890's on ships carrying coffee and sugar from Argentina . These colonies spread across the southern coastal states and into California .
In Argentina , native ant colonies are territorial and aggressive toward one another. DNA tests have shown that the ants in Argentina are twice as genetically diverse as the ants in California . In California , individuals from a San Diego colony will be welcomed by a colony in San Francisco , presumably because the low genetic diversity among the U.S. colonies allows individuals to recognize each other as members of a single colony.
Normally, a lack of genetic diversity is seen as a disadvantage to evolutionary success, and in fact may be a drawback to the Argentine ant in the long term. However, for the immediate future, this invasive species is dominating many native ants that are several times its size, because its sheer numbers and aggressive behaviors overcome opponents. This domination has proven catastrophic not only to other ant species, but also to more unexpected victims. For example, California horned lizards, which feed almost exclusively on Harvester ants, are in serious decline because their favored prey is being decimated by the Argentine ant.
Distribution: Known as "the Huns and Tartars of the insect world," Army ants are found in Africa and Asia as well as South and Central America . New and Old World species that display the army ant syndrome probably shared a common ancestor before the breakup of Gondwana some 100 million years ago. Eciton burchellii inhabits the tropics and subtropics of South and Central America as well as Mexico .
Habitat: E. burchellii prefers hot and humid lowland tropical forests.Appearance: Soldiers have large heads and sickle-shaped mandibles and serve exclusively as a defensive force. Workers have short, clamp-shaped mandibles and are generalists. Diet: Army ants are migratory hunters that feed mainly on hard-bodied creatures such as insects, spiders, and scorpions, but they will eat just about anything they can subdue. Colonies of E. burchellii are enormous, sometimes numbering up to 2 million individuals. They can devastate an area of more than 1,800 square yards in a single day, so they must constantly move to new areas. During what is called the migratory phase, the ants set up a temporary camp called a bivuac in a new site nearly every night. As many as 150,000 to 700,000 worker bodies cover and protect the queen, linking legs and bodies in a mass that measures a meter across. Thousands of larvae are located near the center with the queen, and workers are responsible for feeding them. Larger workers also serve as porters, carrying larvae to new bivouacs. In the morning, the bivouac dissolves into raiding columns that form a fan-shaped front. These raiding columns can travel up to 20 meters per hour with lead workers laying a chemical trail for other workers to follow. Smaller workers lead the column, while larger, formidable soldiers protect the flanks.
Reproduction & Development: The colony moves regularly between the migratory and static phases, both of which are controlled by the reproductive cycle. During the static phase, which is two to three weeks long, the colony remains in the same location. Inside the colony, the queen, now swollen with fertilized eggs, begins laying prodigious numbers of eggs, up to some 30,000 a day, while larvae from the previous static phase spin cocoons and enter the pupal stage. After two or three weeks, the most recently laid eggs hatch into larvae and new workers emerge from cocoons. With all of these new mouths to feed, the colony once again enters the migratory phase.
Mortality — Longevity: The queen and her colony can live 10 - 20 years. Workers generally live about one year, while males die shortly after mating.
Other: Cooperative behavior of army ant colonies takes many forms. When they come to a stream, some species interlock their legs and bodies, forming a bridge up to a meter across upon which others can walk. When caught in a flood, they quickly form a ball that floats down stream. It is also claimed that the jaws of the soldier have been used as sutures to hold together the edges of a wound.
Distribution: Over 1,000 species of Camponotus ants are known worldwide. Nineteen species have been documented in California . They are more common in mountainous and forested areas, but carpenter ants can be found in almost all habitats in the state. Camponotus laevigatus is found throughout the Sierra Nevada in California . The Academy's colony was collected from Mount St. Helena in Napa County , one of the few places to find this species in the Bay area.
Habitat: C. laevigatus usually constructs nests in live or dead trees, stumps, or rotting logs. Other species can be found under rocks or in dead braches. In urban areas, some species nests in buildings, telephone poles, and other wooden structures.
Appearance: About 1/2" long, C. laevigatus is easy to distinguish from other species because of its large size and shiny back color.
Diet: In the wild, carpenter ants feed on both dead and living insects, aphid and scale insect honeydew, and the juices of ripe fruit. They do not sting, but they can inflict a painful bite with their powerful jaws. They also emit a noxious excretion of formic acid when disturbed.
Reproduction & Development: Winged males and queens leave the nest to mate and establish new colonies. These flying ants are sometimes confused with termites.
Mortality Longevity: In a lab, Camponotus queens have lived up to 27 years, and workers have lived for several years. Males die after mating with the queen.
Other: Carpenter ants don't actually eat wood — they bore into wood to make their nests, which are extensive networks of galleries that are usually started in soft, decayed areas. Indoor nests, which may be satellite colonies of larger, outside nests, are sometimes bored into wooden parts of a building or furniture, causing structural damage — usually to areas already compromised by decay or dryrot. Up to 20 satellite colonies may be associated with the main colony that contains the queen.
Disturbed Carpenter ant workers are known to rock furiously back and forth so their mandibles in front and their hindmost body part pound against the nest in rapid bursts — up to 7 strikes within 50 millisecond intervals. This form of communication is called drumming.
Distribution: Honeypot ants are found in Australia, Africa , and North and South America . The term "honeypot ant" actually describes a strategy evolved separately by a number of unrelated species in which one caste has the unique ability to store nutritious fluid for an extended period in distended abdomens — an adaptation to the constraints of the dry season. Myrmecocystusmexicanus is found from Mexico to Colorado , Utah , and California .
Habitat: These ants live indry, semi-arid regions, such as the fringes of deserts or semi-deserts.
Appearance: Queens are born with wings, but tear them off after mating by pushing them back and forth with their hind legs. Workers are small and wingless, while males are small with wings.
Diet: After the rainy season, plants produce so much nectar that there is more than enough food for these ants. During this time of plenty, some of the largest workers in the colony are fed with nectar until the sweet liquid swells their abdomens, often to the size of grapes. These individuals are literally the "honey pots" that hang, like utensils in some kitchens, from the ceilings of nest cavities, holding fast by their claws until their precious stores are required. As the desert's food supply dwindles seasonally, nest mates will stroke the antennae of a storage ant, and it will regurgitate some of the "honey" into the supplicant's mouth. In a sense, Honeypot ants have evolved their own refrigerators, storing food in the cool earth to help the colony survive in an uncertain environment. Because they concentrate nutrients, Honeypot ants are often a source of food for other desert animals, occasionally including humans.
During moister seasons,Honeypot ants of the American Southwest live on the sugary secretions of plants as well as the honeydew of certain insects. They also have the unusual habit of robbing Harvester ants of the genus Pogonomyrmex, especially if their target's cargo is a termite — a favored delicacy of the Honeypots.Longevity: One colony of Myrmecocystus lived in the lab of well-known entomologist Bert Hölldobler for 11 years.
Other:Mymecocystus ants have been known to overrun and take hostages from other ant colonies of their own species. However, this aggressive behavior is not common. Instead, the ants typically assess opponents from different colonies and engage in ritual displays. When an actual face-off takes place, movements seem designed to gauge the strength of counterparts, a kind of pushing and posturing rather than the slashing of deadly mandibles. Somehow, the combatants are able to assess relative strengths and behave accordingly: retreating if overpowered, forcing other colonies to less favorable feeding grounds if a good bluff works, or if a great advantage is assessed, overrunning the neighboring colony, killing the queen, and enslaving workers and larvae.
Distribution: Most Leaf Cutter ant species are native to tropical Central and South America , though a few species occur in the southwestern United States . Atta cephalotes ranges from southern Mexico to Bolivia and Brazil .
Habitat: Colonies are found throughout the tropical rain forests, tropical deciduous forests, and tropical scrub forests. Underground nests can be 20 feet deep and can cover up to one acre.
Appearance: Rust colored with lighter colored legs, Atta cephalotes is noted for its especially large head (hence the name). The huge queen is up to an inch in length. Workers take many forms and sizes, from large soldiers and major workers with their impressive mandibles to the smallest workers, sized to move easily through the narrow galleries of fungal gardens. A soldier may be 10 times longer and weigh several hundred times more than the smallest worker .
Diet: Leaf Cutter ants are true gardeners. They grow their own food by cutting leaves and carrying them back to the nest, where smaller workers then process them further and take them to underground "garden" chambers. All along the way, the leaves are fertilized by their handlers with anal secretions. Fungi then grow on the decaying vegetation, and the ants feed exclusively on the fungus, not the leaves.
Reproduction & Development: These ants swarm in mating flights at the onset of the rainy season. A founding female stores fungus spores inside a pocket in her mouth cavity and uses these spores to start her new nest. After she digs the first chamber for the garden, she deposits the spores, gathers appropriate leaves, and begins laying about 1000 eggs each day. The first group of workers to develop takes over for the queen in caring for the future eggs, larvae, and pupae. The queen has only one job then — to lay the eggs that will build the colony.
Longevity: The queen lives up to 10 years on average, but has been known to live 14 years.
Other: Leaf Cutter ants and the fungus they farm are mutually dependent upon each other for survival. Obviously, the fungus provides the ants with food, but equally important, the fungus receives a warm, moist home and is supplied with fresh, fertilized nutrients.
Leaf-cutter ants are able to start vibrations in their mandibles that help them cut smoothly through leaves. These vibrations also help them to communicate during harvesting missions. For instance, they signal smaller ants to climb onto harvested leaves on the ride home. These hitch-hiking minor workers defend the leaf carriers from flies that try to inject eggs into their bodies.
Leaf-cutter ants are responsible for destroying more vegetation than any other group of animals: they inflict more than a billion dollars in crop damage yearly. However, they also circulate nutrients and aerate huge quantities of soil in forests and grasslands as they construct their subterranean cities.
Distribution: Many ants worldwide are labeled "harvesters," because they collect, store, and eat seeds. In the United States , most Harvester ants are members of the genus Pogonomyrmex, the group described below. Most of the 26 species of Pogonomyrmex in the United States occur west of the Mississippi; only one species occurs east of the Mississippi River .
Habitat: Red Harvester ants live primarily in dry, arid conditions. Nests are constructed in exposed areas — they are up to 15 feet deep and have numerous storage areas (granaries) that hold the collected seeds.
Appearance: Pogonomyrmex barbatus workers are orange to reddish-orange, and they are about 1/2 inch long. All Harvester ants have barbed stingers.
Diet: Red Harvester ants collect seeds primarily from grasses, which they store in their granaries. Workers typically collect seeds by traveling over maintained trails that can extend 30-40 miles from the nest. They also collect other insects and arthropods if they are available. Some workers lay unfertilized eggs that are fed to the larvae and queen.
Reproduction & Development: The reproductive cycle of the Red Harvester ant is typical of many ant species. Only the reproductive females and males have wings — the workers are wingless and sterile. The winged ants engage in late summer mating flights (also called nuptial flights) that are triggered by rain, which serves to synchronize the flight of individuals across many colonies. Each queen mates with several males, tears off her wings, then digs a shallow nest and begins to lay eggs. Queens of most species of Harvester ants, including the Red Harvester, use their body reserves (flight muscles, fat, and other tissue reserves) to sustain themselves and rear their first batch of workers, which emerge after 3 to 4 weeks. The workers then assume the task of food gathering, as servants to the queen and nurses to the offspring.
Longevity: Males die soon after mating, but queens reportedly live up to 30 years and workers live for several months.
Other: Harvester ants are among the most common and easily observed ants in the western United States . Most species are well adapted to desert life. These war-like ants fearlessly bite and sting any intruder and engage in battles with other colonies, both of their own and other species. One "war" was observed to last for 46 days! The stings of most Harvester ants are acutely painful. Characters staked out in Western movies over ant mounds are most likely victims of Harvester ants.
Several Horned lizard species feed almost exclusively on Harvester ants. Their reptilian armor and ability to quickly detoxify Harvester ant venom give these lizards the ability to withstand even the most vicious ant attacks. In areas where Harvesters are being outcompeted by Argentine ants, these Horned lizards have become endangered.