Worker medium-sized, slender, slightly polymorphic. Head rather large, broader behind than in front, with rounded sides and posterior corners and semicircularly excised occipital border, very convex above. Eyes large, convex, broadly elliptical, situated in front of the middle of the head. Ocelli absent. Palpi very short, maxillary pair 5-jointed, labial pair 4-jointed. Mandibles long and large, triangular, with nearly straight lateral borders, a very long curved apical tooth and numerous short denticles along the straight apical border. Clypeus very large and convex, but not distinctly carinate, its anterior border entire or very feebly sinuate in the middle, depressed and projecting over the bases of the mandibles. Frontal area rather large, subtriangular; frontal carinae moderately long, subparallel. Antenna; very long, 12- jointed, the scapes inserted some distance from the posterior corners of the clypeus, rather abruptly incrassated at their tips; the first funicular joint very long and slender, longer than the second and third together, joints '2 to 5 much shorter, subequal, slender, the remaining joints, except the last, shorter and distinctly thicker. Thorax long and narrow; pronotum longer than broad, evenly convex above, narrowed and colliform anteriorly; mesonotum anteriorly long and constricted, subcylindrical, suddenly broadened behind where it joins the small, short, unarmed epinotum, which is rounded and convex above and without distinct base and declivity. Petiole long and slender, much longer than broad, subcylindrical, with a very low rounded node near its posterior end, its ventral surface near the middle more or less convex, its posterior border on each side with a small rounded, projecting lamella, appearing like an acute tooth when the segment is viewed from above. Gaster short, broadly elliptical, its first segment suddenly contracted to the petiole, the tip rather pointed. Legs very long and slender; claws, pulvilli, and last tarsal joint enlarged. Gizzard with long slender sepals, which are not reflected at their anterior ends.
Female much larger than the worker. Head broad, sub triangular; eyes not much larger than in the worker; ocelli well developed Thorax and gaster very broad and massive, flattened above; thorax nearly as broad as long, pronotum small and vertical, overhung by the large depressed mesonotum; epinotum nearly vertical. Petiole short and stout, broader than long, its node low and rounded, more or less impressed in the middle, obliquely truncated or concave behind. Gaster short, nearly as broad as long. Wings very long and ample, decidedly longer than the body, heavily veined, with a narrow closed radial, a large single cubital, and no discoidal cell.
Male somewhat smaller than the largest workers. Head small, broader than long, with very prominent, hemispherical eyes and moderately large ocelli. Mandibles very small, spatulate, with a few minute denticles. Antennae slender and rather short, 13-jointed; scapes elongate, their apical halves somewhat abruptly incrassated; first funicular joint clavate, enlarged at tip, slender at base; remaining joints much shorter, except the last, and slender. Thorax short and massive, the mesonotum broader than the head, very convex and gibbous in front where it overhangs the small mesonotum. Petiole and gaster similar to those in the worker, but the former more flattened above and without a node. Genital appendages very small, narrow, linear; legs long and slender, tarsal claws obsolete, but pulvilli well-developed. Wings ample, distinctly paler than in the female. Head, thorax and gaster much more pilose than in the worker and female.
Pupae not enclosed in cocoons.
This interesting genus is confined to the Old World tropics and ranges over the Indomalayan, Papuan, and Ethiopian Regions, but does not occur in Madagascar (Map 37). It comprises the famous and vicious "tree-ants," or "tailor ants," which make peculiar globular or elliptical nests of leaves on living trees. The leaves are spun together with films of white silk, which is supplied by the larvae. Numerous observers, notably Holland and Green, Wroughton, Rothney, Dodd, Saville Kent, Doflein, Bugnion, the Sarasin Brothers, Jacobson, Kohl, and myself, have described the extraordinary manner in which the workers use the young larvae as animated shuttles.
According to the majority of myrmecologists, the genus Oecophylla , comprises only a single species, smaragdina (Fabricius) , with several geographical races and varieties. A study of the materials that have been accumulating in my collection for the past twenty years, together with the fine series of specimens taken by Lang and Chapin in the Congo, has convinced me that there are really two distinct species: Oe . smaragdina, (Fabricius) of the Indomalayan and Papuan Regions, with the varieties selebensis Emery, gracilior Forel, and gracillima Emery and the subspecies subnitida Emery and virescens (Fabricius) ; and ( E. longinoda (Latreille) of the Ethiopian Region, with the varieties textor Santschi , rubriceps Forel, annectans , new variety , and fusca Emery. Ern. Andre described a form brevinodis , from Sierra Leone, as a distinct species, and Stitz has recently cited it from Spanish Guinea, remarking that longinoda occurs on the coast, brevinodis in the hinterland, and that there are no transitions between the two. He implies also that brevinodis does not make silken nests like longinoda . The abundant Congo series from various nests shows, however, without the slightest doubt, that brevinodis is nothing but the worker minima of longinoda (see Fig. 58c), as Emery maintained as long ago as 1886, and the localities of the material before me show that this species is not confined to the west coastal region. It occurs also in East Africa, Santschii variety textor being from Zanzibar. Several authors have cited the true smaragdina- from East Africa. Unfortunately I have little material from that region and what I have is certainly longinoda , presumably belonging to textor , though this variety seems to me to be poorly characterized and possibly not distinct from the typical form of the species. I am unable to say, therefore, whether Oe. smaragdina , actually occurs on the African continent.
According to Emery, longinoda is the most primitive of the existing forms of Oecophylla , because most closely allied to Oe. sicula , which he described from the Miocene amber of Sicily. In the Baltic amber I have recognized two species of the genus, Oe. brischkei Mayr and brevinodis Wheeler . As the latter name is preoccupied by brevinodis Andre , which was based, as I have shown, on the minima worker of longinoda , I suggest that the fossil species be called crassinoda (new name). In the shape of the petiole both of the Baltic amber forms, being of Lower Oligocene age and therefore older than sicula , are also more like longinoda , and especially its smaller workers, than the Oriental smaragdina .
Molecular Biology and Genetics
Statistics of barcoding coverage
|Specimen Records:||97||Public Records:||65|
|Specimens with Sequences:||94||Public Species:||1|
|Specimens with Barcodes:||92||Public BINs:||9|
|Species With Barcodes:||3|
Weaver ants or green ants (genus Oecophylla) are eusocial insects of the family Formicidae (order Hymenoptera). Weaver ants are obligately arboreal and are known for their unique nest building behaviour where workers construct nests by weaving together leaves using larval silk. Colonies can be extremely large consisting of more than a hundred nests spanning numerous trees and contain more than half a million workers. Like many other ant species, weaver ants prey on small insects and supplement their diet with carbohydrate-rich honeydew excreted by small insects (Hemiptera). Oecophylla workers exhibit a clear bimodal size distribution, with almost no overlap between the size of the minor and major workers. The major workers are approximately 8–10 mm (0.31–0.39 in) in length and the minors approximately half the length of the majors. There is a division of labour associated with the size difference between workers. Major workers forage, defend, maintain, and expand the colony whereas minor workers tend to stay within the nests where they care for the brood and 'milk' scale insects in or close to the nests. Oecophylla weaver ants vary in color from reddish to yellowish brown dependent on the species. Oecophylla smaragdina found in Australia often have bright green gasters. These ants are highly territorial and workers aggressively defend their territories against intruders. Because of their aggressive behaviour, weaver ants are sometime used by indigenous farmers, particularly in southeast Asia, as natural biocontrol agents against agricultural pests. Although Oecophylla weaver ants lack a functional sting they can inflict painful bites and often spray formic acid directly at the bite wound resulting in intense discomfort.
- †Oecophylla atavina
- †Oecophylla bartoniana
- †Oecophylla brischkei
- †Oecophylla crassinoda
- †Oecophylla eckfeldiana
- †Oecophylla grandimandibula
- †Oecophylla leakeyi
- †Oecophylla longiceps
- †Oecophylla megarche
- †Oecophylla obesa
- †Oecophylla perdita
- †Oecophylla praeclara
- †Oecophylla sicula
- †Oecophylla superba
- †Oecophylla xiejiaheensis
The weaver ants belong to the ant genus Oecophylla (subfamily Formicinae) which contains two closely related living species: O. longinoda found in Sub-Saharan Africa and O. smaragdina found in southern India, southeast Asia, and Australia. They are provisionally placed in a tribe of their own, Oecophyllini. The weaver ant genus Oecophylla is relatively old, and 15 fossil species have been found from the Eocene to Miocene deposits. Two other genera of weaving ants, Polyrhachis and Dendromyrmex, also use larval silk in nest construction, but the construction and architecture of their nests are simpler than those of Oecophylla. In Australia, Oecophylla smaragdina is found in the tropical coastal areas as far south as Rockhampton and across the coastal tropics of the Northern Territory down to Broome in West Australia.
The common features of the genus include an elongated first funicular segment, presence of propodeal lobes, helcium at midheight of abdominal segment 3 and gaster capable of reflexion over the mesosoma. Males have vestigial pretarsal claws.
Weaver ant colonies are founded by one or more mated females (queens). A queen lays her first clutch of eggs on a leaf and protects and feeds the larvae until they develop into mature workers. The workers then construct leaf nests and help rear new brood laid by the queen. As the number of workers increases, more nests are constructed and colony productivity and growth increase significantly. Workers perform tasks that are essential to colony survival, including foraging, nest construction, and colony defense. The exchange of information and modulation of worker behaviour that occur during worker-worker interactions are facilitated by the use of chemical and tactile communication signals. These signals are used primarily in the contexts of foraging and colony defense. Successful foragers lay down pheromone trails that help recruit other workers to new food sources. Pheromone trails are also used by patrollers to recruit workers against territorial intruders. Along with chemical signals, workers also use tactile communication signals such as attenation and body shaking to stimulate activity in signal recipients. Multimodal communication in Oecophylla weaver ants importantly contributes to colony self-organization. Like many other ant species, Oecophylla workers exhibit social carrying behavior as part of the recruitment process, in which one worker will carry another worker in its mandibles and transport it to a location requiring attention.
Nest building behaviour
Oecophylla weaver ants are known for their remarkable cooperative behaviour used in nest construction. Possibly the first description of weaver ant's nest building behaviour was made by the English naturalist Joseph Banks, who took part in Captain James Cook's voyage to Australia in 1768. An excerpt from Joseph Banks' Journal (cited in Hölldobler and Wilson 1990) is included below:
The ants...one green as a leaf, and living upon trees, where it built a nest, in size between that of a man's head and his fist, by bending the leaves together, and gluing them with whitish paperish substances which held them firmly together. In doing this their management was most curious: they bend down four leaves broader than a man's hand, and place them in such a direction as they choose. This requires a much larger force than these animals seem capable of; many thousands indeed are employed in the joint work. I have seen as many as could stand by one another, holding down such a leaf, each drawing down with all his might, while others within were employed to fasten the glue. How they had bent it down I had not the opportunity of seeing, but it was held down by main strength, I easily proved by disturbing a part of them, on which the leaf bursting from the rest, returned to its natural situation, and I had an opportunity of trying with my finger the strength of these little animals must have used to get it down.
The weaver ant's ability to build capacious nests from living leaves has undeniably contributed to their ecological success. The first phase in nest construction involves workers surveying potential nesting leaves by pulling on the edges with their mandibles. When a few ants have successfully bent a leaf onto itself or drawn its edge toward another, other workers nearby join the effort. The probability of a worker joining the concerted effort is dependent on the size of the group, with workers showing a higher probability of joining when group size is large. When the span between two leaves is beyond the reach of a single ant, workers form chains with their bodies by grasping one another's petiole (waist). Multiple intricate chains working in unison are often used to ratchet together large leaves during nest construction. Once the edges of the leaves are drawn together, other workers retrieve larvae from existing nests using their mandibles. These workers hold and manipulate the larvae in such a way that causes them to excrete silk. They can only produce so much silk, so the larva will have to pupate without a cocoon. The workers then maneuver between the leaves in a highly coordinated fashion to bind them together. Weaver ant's nests are usually elliptical in shape and range in size from a single small leaf folded and bound onto itself to large nests consisting of many leaves and measure over half a meter in length. The time required to construct a nest varies depending on leaf type and eventual size, but often a large nest can be built in significantly less than 24 hours. Although weaver ant's nests are strong and impermeable to water, new nests are continually being built by workers in large colonies to replace old dying nests and those damaged by storms.
Positive and negative interactions with crop plants
Large colonies of Oecophylla weaver ants consume significant amounts of food, and workers continuously kill a variety of arthropods (primarily other insects) close to their nests. Insects are not only consumed by workers, but this protein source is necessary for brood development. Because weaver ant workers hunt and kill insects that are potentially harmful plant pests, trees harboring weaver ants benefit from having decreased levels of herbivory. They have traditionally been used in biological control in Chinese and Southeast Asian citrus orchards from at least 400 AD. Many studies have shown the efficacy of using weaver ants as natural biocontrol agents against agricultural pests. The use of weaver ants as biocontrol agents has especially been effective for fruit agriculture, particularly in Australia and southeast Asia. Fruit trees harboring weaver ants produce higher quality fruits, show less leaf damage by herbivores, and require fewer applications of synthetic pesticides. Farmers in Southeast Asia often build rope bridges between trees and orchards to actively recruit ants to unoccupied trees. Established colonies are often supplemented with food to promote faster growth and to deter emigration.
Oecophylla colonies may not be entirely beneficial to the host plants. Studies indicate that the presence of Oecophylla colonies may also have negative effects on the performance of host plants by reducing fruit removal by mammals and birds and therefore reducing seed dispersal and by lowering the flower-visiting rate of flying insects including pollinators. Weaver ants also have an adverse effect on tree productivity by protecting sap feeding insects such as scale insects and leafhoppers from which they collect honeydew. By protecting these insects from predators they increase their population and increase the damage they cause to trees.
Weaver ants as food and medicine
Weaver ants are one of the most valued types of insects eaten by humans (entomophagy). In addition to being used as a biological control agent to increase plant production, weaver ants can be utilized directly as a protein and food source since the ants (especially the ant larvae) are edible and high in protein and fatty acids. In some countries the weaver ant is a highly priced delicacy harvested in vast amounts and in this way contributing to local socioeconomics. In Northeastern Thailand the price of weaver ant larvae is twice the price of good quality beef and in a single Thai province ant larvae worth 620.000 USD are harvested every year. It has furthermore been shown that the harvest of weaver ants can be maintained while at the same time using the ants for biocontrol of pest insects in tropical plantations, since the queen larvae and pupae that are the primary target of harvest, are not vital for colony survival. It follows that weaver ants convert damaging pest insects into valuable weaver ant biomass that can be utilized as a food source. The ants may in this way provide double benefits to agriculture.
The larvae of weaver ants are also collected commercially as an expensive feed for insect eating birds in Indonesia and the worker ants are used in traditional medicine in e.g. India and China.
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