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Oecophylla longinoda

By Timothy Woodruff

Geographic Range

The African weaver ant occupies the tropical rain forests of Sub-Saharan Africa. (Holldobler and Wilson, 1977; Holldobler and Wilson, 1990; Holldobler and Wilson, 1994)

Habitat

Weaver ants are arboreal, living in heavily forested areas. The way in which weaver ants build their nests reduces spatial limitations to their colonies, and one colony may occupy several trees at one time. (Holldobler and Wilson, 1990; Holldobler and Wilson, 1994; Wheeler, 1910)

Physical Description

Oecophylla longinoda are relatively large ants, with the bodies of workers averaging 6 mm in length. The body of the ant is segmented and is divided into three main parts; the head, thorax, and abdomen. Like all insects, six legs are connected to the thoracic region. These ants range from orange to dark brown in color. Erect hairs cover the surface of the gaster while a finer pubescence encompasses the rest of its body. The eyes are well developed with eyespots. The clypeus, the large shield-like plate on the front of its head, is large and convex with the outer edges overhanging the basal borders of the mandibles. It has 12-segmented antennae with the first segment of the antennae longer than the second and the third put together. Its mandibles are extended, and have triangular elongated teeth that cross one another when at rest. The thorax is very constricted in the mesonotal region. The petiole between the thorax and abdomen is thin in dorsal view, but looks low and rounded in the side view. The gaster has a visible acidopore. On the ants' feet, there are powerful suction pads called arolia, allowing this ant to maintain heavier loads than other ants. Another important characteristic of the weaver ant is the presence of the rectal gland and the sternal gland, both of which are located near the anus and are used to secrete chemicals to recruit nestmates when circumstances arise that require the attention of a group of ants. (Holldobler and Wilson, 1977; Holldobler and Wilson, 1990; Holldobler and Wilson, 1994; Taylor, 1998; Wheeler, 1910)

  • Average length
    6 mm
    0.24 in

Development

There are four stages to the life cycle of weaver ants: Egg; Larvae; Pupae; Adult. It takes approximately 30 days to develop from an egg into an adult worker. There are also at least three larval instars (larval growth periods) before the immature ant can pupate. O. longinoda pupates without enclosing itself in silk, as it spends its silk on nest construction. Instead, it remains exposed as it undergoes a complete metamorphosis from its larval, grub-like form into an adult ant. (Holldobler and Wilson, 1977; Holldobler and Wilson, 1990; Holldobler and Wilson, 1994; Wilson and Holldobler, 1980)

Reproduction

After her nuptual (copulatory) flight, the new queen will find a protected area on the outer regions of a tree. She chooses the outer regions probably because other queens may have chosen the same tree and the farther away they are from eachother the safer their brood are from the others' workers. The single queen is responsible for all the reproductive needs of the colony. She lays one hundred eggs per day, which are carried to brood piles to be cared for by the minor workers. (Holldobler and Wilson, 1977; Holldobler and Wilson, 1990; Holldobler and Wilson, 1994; Tan, 2001; Wilson and Holldobler, 1980)

  • Average time to independence
    30 days

Like all ants, the very first brood is cared for by the queen. She feeds the larvae regurgitated body fluids and unfertalized eggs, often losing up to 60% of her body weight in the process, as she will not leave her brood during this time to go out and forage. After the first workers develop, they take over brood care and the queen devotes the rest of her time and energy to egg laying. In addition to caring for eggs and larvae, workers care for the queen by feeding and cleaning her.

Although minor workers are the primary nursemaids, once the larvae reach their maximum size they are cared for equally by the major and minor workers. (Holldobler and Wilson, 1990)

  • Parental Investment
  • pre-fertilization
    • provisioning
    • protecting
      • female

Lifespan/Longevity

Little is known about the lifespan of this species.

Behavior

Their well-developed system of communication, as well as their caste system enhances the capabilities of the colony; however, individual ants are mostly incapable of surviving on their own. The caste system contains three forms of adult females: the queen, the major workers, and the minor workers. The major workers do most of the external work for the colony, including building nests, foraging for food, and exploring new territory. The minor workers are responsible for taking care of the eggs and young larvae.

In general, African weaver ants are a very aggressive group. Not only do they not hesitate to attack any intruding insects, especially other colonies of weaver ants, but if a larger animal disturbs their nest, thousands of ants will drop down off of the tree to attack the intruder, biting it with their mandibles and spraying formic acid on the wounds. Any animal passing too close or spending too much time near the tree of O. longinoda can be considered a threat to the colony and may be attacked. Often, the older ants that no longer have the industry of younger workers will stand guard at the edges of the nests, and will be the first to drop down from the nest to defend the colony.

Weaver ants build their nests from the leaves of trees, bending the leaves into place and then binding them together with silk produced by larvae. When building a new nest, ants begin by walking along the edges of leaves, occasionally pulling up on the edges to test the flexibility of the leaf. If the ant succeeds in turning up the leaf even the slightest bit, other ants join in forming chains of their bodies. By grasping the thoracic region of another ant, an ant chain long enough to extend between the ends of a leaf can be made. The ants in the chain then pull the ends of the leaves together until they are next to each other. Then other ants seal the leaves together by applying the silk from larvae that are in their final instar. Holding the larva and touching it with antennae in a certain way signals the larva to produce silk, and the ant can weave the two leaves together. It is in this last of at least three larval instars that larvae might be recruited to contribute silk to the building of nests. The larvae do not build cocoons because of the protection afforded them by the nest and because they have given up their silk for nest construction. By building nests in this way, and having an unlimited number of nests per colony, weaver ants have no spatial limitations for their colony, and so can occupy several trees at one time. With this much room, it is not uncommon for single colonies to have populations of a half million or more ants. (Holldobler and Wilson, 1977; Holldobler and Wilson, 1990; Holldobler and Wilson, 1994; Holldobler, 1998; Wilson and Holldobler, 1980)

Home Range

When the ants encounter a new home range, they randomly place drops of fluid from the rectal vesicle. They can then distinguish their territory from a foreign colonies' by the odor of these spots. (Holldobler and Wilson, 1990; Holldobler and Wilson, 1994; Holldobler, 1998; Tan, 2001)

Communication and Perception

Oecophylla longinoda have developed at least 5 systems by which an individual ant can gather together a large group for the purpose of exploring new territory, attacking an enemy, or obtaining food. The first system of communication is used for the recruitment of ants to new terrain. For example, when weaver ants approach a gap in the ground, they will need to recruit other ants to help build a bridge with their bodies in order to cross the gap. A combination of chemical and tactile signals is used to recruit the other ants. The chemical signal is a secretion from one of two glands located near the anus. These secretions are laid down as a trail for the other ants to follow, which other ants then "smell" with their antennae.

The second system also recruits ants by means of an odor trail, but for the purpose of finding new food sources. Foraging communication includes odor trails, tactual stimuli functioning during mouth opening, antennation (moving the antennae), and head waggling.

The third type of communication leads to emigration to new sites. When ants encounter a new home range, they randomly place drops of fluid from the rectal vesicle. They can then distinguish their territory from a foreign colonies' by the odor of these spots.

The fourth system serves the purpose of short-range recruitment to defend against territorial intruders. This “alarm” pheromone is released when the terminal abdominal sternite is completely visible and hauled for a limited distance over surfaces to release an attractant from the sternal gland.

Finally, for long-range recruitment of defense against intruders, a combination of odor trails, as well as antennation and extreme "body jerking", are used. (Holldobler and Wilson, 1990; Holldobler and Wilson, 1994; Holldobler, 1998)

Food Habits

The African weaver ants are primarily insectivorous, attacking and eating any ants or other insects that invade their nest. They will even attack and eat weaver ants from other colonies. Another main staple food for the weaver ant is the honeydew excrement from herds of scale insects colonies often maintain. (Holldobler and Wilson, 1977; Holldobler and Wilson, 1990; Holldobler and Wilson, 1994)

  • Animal Foods
  • body fluids

Predation

Certain species of caterpillars use chemical mimicry to enter nests and eat eggs and larvae, but little more is known of the predators of this species. (Holldobler and Wilson, 1990)

Economic Importance for Humans: Positive

African weaver ants can be used to protect cacao tree crops. The African weaver ant effectively controls certain species of Homoptera (an order of bugs), a common pest of the cacao. The mealy bug, one species of Homoptera, transmits Cacao Black Pod Disease as it moves from tree to tree feeding on the leaves. Utilizing African weaver ants to control populations of these insects can greatly reduce crop damages due to this disease. (Holldobler and Wilson, 1990; Taylor, 1998)

  • Positive Impacts
  • controls pest population

Economic Importance for Humans: Negative

The African Weaver ant has no negative economic impact on humans.

  • Negative Impacts
  • injures humans
    • bites or stings

Conservation Status

This species is in no danger and has no special status.

Other Comments

The African weaver ant gets its name because of the way the ants use larval silk in order to "weave" leaves together to form their nests.

Contributors

Sara Diamond (editor), Animal Diversity Web.

Timothy Woodruff (author), Southwestern University, Stephanie Fabritius (editor), Southwestern University.

Glossary

Ethiopian

living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.

World Map

arboreal

Referring to an animal that lives in trees; tree-climbing.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

delayed fertilization

a substantial delay (longer than the minimum time required for sperm to travel to the egg) takes place between copulation and fertilization, used to describe female sperm storage.

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

eusocial

the condition in which individuals in a group display each of the following three traits: cooperative care of young; some individuals in the group give up reproduction and specialize in care of young; overlap of at least two generations of life stages capable of contributing to colony labor

fertilization

union of egg and spermatozoan

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

insectivore

An animal that eats mainly insects or spiders.

internal fertilization

fertilization takes place within the female's body

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

metamorphosis

A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

pheromones

chemicals released into air or water that are detected by and responded to by other animals of the same species

rainforest

rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.

scent marks

communicates by producing scents from special gland(s) and placing them on a surface whether others can smell or taste them

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

social

associates with others of its species; forms social groups.

sperm-storing

mature spermatozoa are stored by females following copulation. Male sperm storage also occurs, as sperm are retained in the male epididymes (in mammals) for a period that can, in some cases, extend over several weeks or more, but here we use the term to refer only to sperm storage by females.

tactile

uses touch to communicate

terrestrial

Living on the ground.

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

vibrations

movements of a hard surface that are produced by animals as signals to others

visual

uses sight to communicate

year-round breeding

breeding takes place throughout the year

References

Holldobler, B., E. Wilson. 1977. Weaver Ants. Scientific American, 237: 146-154.

Holldobler, B. 1998. Cooperation and Communication of Weaver Ants (Oecophylla). Jiussi News, 40.

Holldobler, B., E. Wilson. 1994. Journey to the Ants: A Story of Scientific Exploration. London, England: The Belknap Press of Harvard University.

Holldobler, B., E. Wilson. 1990. The Ants. Cambridge, Massachusetts: The Belknap Press of Harvard University.

Tan, T. 2001. "Weaver Ants" (On-line). Accessed February 16, 2005 at http://www.naturia.per.sg/buloh/inverts/weaver_ants.htm.

Taylor, B. 1998. The Ants of West Africa. Nottingham, U.K.: University Press.

Taylor, B. 2004. "The Ants of Africa" (On-line). Accessed February 16, 2005 at http://antbase.org/ants/africa/oecvariability.htm.

Wheeler, W. 1910. Ants: Their Structure, Development and Behavior. New York: Columbia University Press.

Wilson, E., B. Holldobler. 1980. Sex differences in cooperative silk-spinning by weaver ant larvae. Proceedings of the National Academy of Sciences of the United States of America, 77: 2343-2347.

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