Leptanilla japonica
Encyclopedia
Leptanilla japonica is an uncommon highly migratory, subterranean ant
found in Japan
. They are tiny insect
s, with workers measuring about 1.2 mm and queens
reaching to about 1.8 mm, and live in very small colonies
of only a few hundred individuals at a time (as compared to the 60,000 to 20,000,000 individuals of legionary ant
colonies.) Its sexual development follows a seasonal cycle that affects the colony’s migration
and feeding habits, and vice versa. L. japonica exhibits specialized predation
, with prey consisting mainly of geophilomorph centipede
s, a less reliable food source that also contributes to their high rate of nest migration. Like ants of genera
Amblyopone
and Proceratium, the Leptanilla
genus engages in larval hemolymph feeding
(LHF), with the queen using no other form of sustenance. LHF is an advantageous alternative to the more costly cannibalism
. Unlike any other ant, however, members of Leptanilla, including L. japonica, have evolved
a specialized organ dubbed the “larval hemolymph tap” that reduces the damage LHF inflicts on the larva
e. LHF has become this species' main form of nutrition.
Leptanillinae
along with about 30 other known species. Leptanillines were once classified as a tribe
of Dorylinae, the subfamily of Old World driver ants. They were raised to subfamily status upon further examination of their unusual larval morphology
Larvae are smaller, closer to 0.8 mm, with specialized features used in feeding and nest migration. They have relatively large bodies covered in minute hairs and their hairless heads are quite small, a characteristic called stenocephaly; this feature evolved to help large groups of larvae feed on one centipede body at once Their mandibles also developed to help them feed; they are directed outwards and armed with sharp teeth, enabling the larvae to eat without assistance from the workers. Another unusual structure lies on the ventral or bottom side of the first segment of the larvae’s thorax
, also called their prothorax
; workers grab on to this with their lower mouthparts, which are distinct from their mandibles, when transporting larvae during migration. The “larval hemolymph tap” is the Leptanilla larvae’s most unique feature and was formerly thought to be a spiracle
. Their spiracles are simply very, very small. The “tap” consists of a duct that connects to their hemolymph
, with an opening surrounded by a small hairless area on the fourth abdominal segment. This specialized organ greatly facilitates LHF.
Colonies are very small, with average worker populations numbering only 100-200 individuals. Research suggests that, based on the ant’s cyclical development and reproduction, worker populations are renewed annually, with most workers living for about one year.
When migrating either to prey or a new nest site, workers attach their lower mouthparts to the larvae’s prothoracic structure and carry them along their body, ventral side to ventral side, with the larva’s head pointing forwards. When agitated, however, workers will also simply grab the larva behind the head with their mandibles and drag them.
Queens are larger than workers; they have eyes, but no wings. The posterior or last segment of their abdomen, also called their gaster
, is very large in proportion to the rest of their bodies.
Males measure roughly 1.3 mm in size, only a little bigger than the workers, and are unusual in having hairy eyes. They are the only caste with wings, albeit rather small wings. One wing actually consists of two parts: the forewing is larger and has veins; the hindwing is much smaller with no veins. Their mandibles are also different from the females’; whereas the workers and queens mandibles are prominent and mobile, the males’ mandibles are little more than small lobes held close to their head. Male ants of this species have been difficult to find in conjunction with workers and queens, and thus their behavior has not been observed and recorded as extensively as that of the females.
, yearly cycles of a larval-growing stage and an egg-laying stage. The active egg-laying stage starts in late spring and ends in late fall. In a very short period in midsummer, the queen lays a batch of roughly 200 eggs while last year’s hatch of larvae pupate
, or undergo metamorphosis
to change from larvae to adults; hatching and adult emergence also occur around the same time. The new larvae develop quickly and hibernate
during the winter. Late spring comes and the cycle repeats.
The queen’s gaster remains contracted for all of the larval-developing stage, reaching no greater than 0.35 mm in diameter. At the onset of spring, she enters physogastry, a phase in which her gaster greatly expands, while the first few larvae show signs of pupation. Her gaster swells with egg-filled ovarioles and grows up to 1.1 mm in diameter. In spite of their size, queens at this stage are very mobile, in contrast to their near motionlessness during the larval-growing stage.
Very soon after physogastry begins, the queen starts laying eggs in a continuous string, with the occasional help of nearby workers. They grab the eggs with their mandibles and gently pull them away from her cloaca
, the orifice of her reproductive tract.
This is only one of many of the workers’ jobs during the egg-laying stage. During this time, workers cease foraging
and migrating to focus on caring for the nest. Workers help larvae get rid of their digestive tracts, a process necessary for pupation, and occasionally eat their feces. They also help them shed their larval skin.
secretion from their sternal side, though travel is disorganized and mostly individual. While roughly half of the workers hunts, the other half engages in grooming, larval care, or stands as guards at the edges of the brood pile. The guard ants almost always assume the same position: they face the outside with their anterior end lifted, their forelegs raised, and their mandibles open. Should anything come close, they quickly charge it.
The other half of the workers is occupied with finding, attacking, and paralyzing the species main, if not only, prey, geophilomorph centipedes. Sufficient paralysis can be accomplished with a small number of ants within 10-15 minutes. Most of the time, the workers pull the centipede to the brood pile, with the colony occasionally moving towards the prey as well to meet somewhere in the middle. A few times, however, researchers observed the colony move entirely to the prey site without moving the centipede. During such migrations, workers attached to the larvae’s prothoracic structures to carry them to the paralyzed prey. As previously described, the larvae’s body and mandible shape make for easy feeding. They rip away the outer tissue, and the workers eat from the holes the larvae make.
Predation is active during the larval-growing stage, but stops during the egg-laying stage along with migration. The main source of nutrition during this stage is the larvae themselves.
The physicality of the queen’s LHF follows. She strokes a mature larva with her antennae
, then holds the posterior end with all six legs
, lying on her side and placing her lower mouthparts on the body. She turns the body around, feeling with her mandibles until she finds the “larval hemolymph tap” in the fourth abdominal segment. The lack of lapping movements of the queen’s mouthparts and the lack of larval muscles along the duct organ suggest that the hemolymph is ingested via the queen’s effort. Hemolymph flow would cease by itself when the queen released the larva or by the hemolymph congealing at the opening.
LHF evolved as a less costly form of last-resort nutrition than cannibalism. Many ant species engage in trophic egg
consumption in which the workers have sterile eggs that the ants can feed on. Leptanilla workers, however, do not have ovarioles and thus do not have that option. Because it has never been observed, mouth-to-mouth feeding, or oral trophallaxis
, is thought to be absent from this genus. LHF is seen in Amblyopone and Proceratium, but those genera have much larger populations, ranging from 60,000 to 20,000,000 workers per colony. With so many individuals at the queen’s disposal, severely damaging the larvae she feeds on would have a negligible negative impact on her reproductive fitness. The queens of Leptanilla, on the other hand, cannot afford such a risk with colonies of only 100-200 individuals; an organ reducing the damage of LHF would be highly selected for in such a species. It also allows for the synchronization and cyclical nature of brood development. The absence of trophic eggs, the cost of cannibalism, the specialized predation of sporadic prey, the cyclical and synchronous colony maturation, and the reduced cost of LHF via the “larval hemolymph tap” have all allowed for LHF to become one of this genus’ main feeding habits.
Ant
Ants are social insects of the family Formicidae and, along with the related wasps and bees, belong to the order Hymenoptera. Ants evolved from wasp-like ancestors in the mid-Cretaceous period between 110 and 130 million years ago and diversified after the rise of flowering plants. More than...
found in Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
. They are tiny insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...
s, with workers measuring about 1.2 mm and queens
Queen ant
A queen ant is an adult, reproducing female ant in an ant colony; generally she will be the mother of all the other ants in that colony. Some female ants do not need to mate to produce offspring, reproducing through asexual parthenogenesis or cloning and all of those offspring will be female.Ant...
reaching to about 1.8 mm, and live in very small colonies
Ant colony
An ant colony is an underground lair where ants live, eat and mate. Colonies consist of a series of underground chambers, connected to each other and the surface of the earth by small tunnels. There are rooms for nurseries, food storage, and mating...
of only a few hundred individuals at a time (as compared to the 60,000 to 20,000,000 individuals of legionary ant
Army ant
The name army ant is applied to over 200 ant species, in different lineages, due to their aggressive predatory foraging groups, known as "raids", in which huge numbers of ants forage simultaneously over a certain area, attacking prey en masse.Another shared feature is that, unlike most ant...
colonies.) Its sexual development follows a seasonal cycle that affects the colony’s migration
Animal migration
Animal migration is the relatively long-distance movement of individuals, usually on a seasonal basis. It is a ubiquitous phenomenon, found in all major animal groups, including birds, mammals, fish, reptiles, amphibians, insects, and crustaceans. The trigger for the migration may be local...
and feeding habits, and vice versa. L. japonica exhibits specialized predation
Predation
In ecology, predation describes a biological interaction where a predator feeds on its prey . Predators may or may not kill their prey prior to feeding on them, but the act of predation always results in the death of its prey and the eventual absorption of the prey's tissue through consumption...
, with prey consisting mainly of geophilomorph centipede
Centipede
Centipedes are arthropods belonging to the class Chilopoda of the subphylum Myriapoda. They are elongated metameric animals with one pair of legs per body segment. Despite the name, centipedes can have a varying number of legs from under 20 to over 300. Centipedes have an odd number of pairs of...
s, a less reliable food source that also contributes to their high rate of nest migration. Like ants of genera
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
Amblyopone
Amblyopone
Amblyopone is a genus of amblyoponine ants.-Description:Workers of Amblyopone have a well-developed sting, elongate mandibles and reduced or absent eyes...
and Proceratium, the Leptanilla
Leptanilla
Leptanilla is a genus of ant in the subfamily Leptanillinae. Like other genera in this subfamily, the queen is fed by the hemolymph of their own larvae, which have specialized processes for this purpose.-Biology:...
genus engages in larval hemolymph feeding
Larval hemolymph feeding
Larval hemolymph feeding is a behaviour trait found in the queens of some species of ant. This is found mainly in the ants of the subfamily Amblyoponinae and give them the other name of Dracula ant. In colonies of the Amblyopone silvestrii the queens feed on the hemolymph of their larvae when food...
(LHF), with the queen using no other form of sustenance. LHF is an advantageous alternative to the more costly cannibalism
Cannibalism (zoology)
In zoology, cannibalism is the act of one individual of a species consuming all or part of another individual of the same species as food. Cannibalism is a common ecological interaction in the animal kingdom and has been recorded for more than 1500 species...
. Unlike any other ant, however, members of Leptanilla, including L. japonica, have evolved
Evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...
a specialized organ dubbed the “larval hemolymph tap” that reduces the damage LHF inflicts on the larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
e. LHF has become this species' main form of nutrition.
Taxonomy
The genus Leptanilla belongs to the subfamilyFamily (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Leptanillinae
Leptanillinae
Leptanillinae is a subfamily of ants. They are further divided into the tribes Anomalomyrmini and Leptanillini.In all Leptanillini the larva feed their hemolymph to the queen through specialized processes on their prothorax and third abdominal segment...
along with about 30 other known species. Leptanillines were once classified as a tribe
Tribe (biology)
In biology, a tribe is a taxonomic rank between family and genus. It is sometimes subdivided into subtribes.Some examples include the tribes: Canini, Acalypheae, Hominini, Bombini, and Antidesmeae.-See also:* Biological classification* Rank...
of Dorylinae, the subfamily of Old World driver ants. They were raised to subfamily status upon further examination of their unusual larval morphology
Morphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
Morphology and description
L. japonica is subterranean, migratory, and a very small ant, measuring only 1.2 mm for workers and 1.8 mm for queens2. Workers are yellow and blind.Larvae are smaller, closer to 0.8 mm, with specialized features used in feeding and nest migration. They have relatively large bodies covered in minute hairs and their hairless heads are quite small, a characteristic called stenocephaly; this feature evolved to help large groups of larvae feed on one centipede body at once Their mandibles also developed to help them feed; they are directed outwards and armed with sharp teeth, enabling the larvae to eat without assistance from the workers. Another unusual structure lies on the ventral or bottom side of the first segment of the larvae’s thorax
Thorax (insect anatomy)
The thorax is the mid section of the insect body. It holds the head, legs, wings and abdomen. It is also called mesosoma in other arthropods....
, also called their prothorax
Prothorax
The prothorax is the foremost of the three segments in the thorax of an insect, and bears the first pair of legs. Its principal sclerites are the pronotum , the prosternum , and the propleuron on each side. The prothorax never bears wings in extant insects, though some fossil groups possessed...
; workers grab on to this with their lower mouthparts, which are distinct from their mandibles, when transporting larvae during migration. The “larval hemolymph tap” is the Leptanilla larvae’s most unique feature and was formerly thought to be a spiracle
Spiracle
Spiracles are openings on the surface of some animals that usually lead to respiratory systems.-Vertebrates:The spiracle is a small hole behind each eye that opens to the mouth in some fishes. In the primitive jawless fish the first gill opening immediately behind the mouth is essentially similar...
. Their spiracles are simply very, very small. The “tap” consists of a duct that connects to their hemolymph
Hemolymph
Hemolymph, or haemolymph, is a fluid in the circulatory system of some arthropods and is analogous to the fluids and cells making up both blood and interstitial fluid in vertebrates such as birds and mammals...
, with an opening surrounded by a small hairless area on the fourth abdominal segment. This specialized organ greatly facilitates LHF.
Colonies are very small, with average worker populations numbering only 100-200 individuals. Research suggests that, based on the ant’s cyclical development and reproduction, worker populations are renewed annually, with most workers living for about one year.
When migrating either to prey or a new nest site, workers attach their lower mouthparts to the larvae’s prothoracic structure and carry them along their body, ventral side to ventral side, with the larva’s head pointing forwards. When agitated, however, workers will also simply grab the larva behind the head with their mandibles and drag them.
Queens are larger than workers; they have eyes, but no wings. The posterior or last segment of their abdomen, also called their gaster
Gaster
The gaster is the bulbous posterior portion of the metasoma found in Apocrita Hymenoptera . This begins with abdominal segment III on most ants, but some make a postpetiole out of segment III, in which case the gaster begins with abdominal segment IV....
, is very large in proportion to the rest of their bodies.
Males measure roughly 1.3 mm in size, only a little bigger than the workers, and are unusual in having hairy eyes. They are the only caste with wings, albeit rather small wings. One wing actually consists of two parts: the forewing is larger and has veins; the hindwing is much smaller with no veins. Their mandibles are also different from the females’; whereas the workers and queens mandibles are prominent and mobile, the males’ mandibles are little more than small lobes held close to their head. Male ants of this species have been difficult to find in conjunction with workers and queens, and thus their behavior has not been observed and recorded as extensively as that of the females.
Development and reproduction
L. japonica develops and reproduces in synchronousSynchronization
Synchronization is timekeeping which requires the coordination of events to operate a system in unison. The familiar conductor of an orchestra serves to keep the orchestra in time....
, yearly cycles of a larval-growing stage and an egg-laying stage. The active egg-laying stage starts in late spring and ends in late fall. In a very short period in midsummer, the queen lays a batch of roughly 200 eggs while last year’s hatch of larvae pupate
Pupa
A pupa is the life stage of some insects undergoing transformation. The pupal stage is found only in holometabolous insects, those that undergo a complete metamorphosis, going through four life stages; embryo, larva, pupa and imago...
, or undergo metamorphosis
Metamorphosis
Metamorphosis is a biological process by which an animal physically develops after birth or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation...
to change from larvae to adults; hatching and adult emergence also occur around the same time. The new larvae develop quickly and hibernate
Hibernation
Hibernation is a state of inactivity and metabolic depression in animals, characterized by lower body temperature, slower breathing, and lower metabolic rate. Hibernating animals conserve food, especially during winter when food supplies are limited, tapping energy reserves, body fat, at a slow rate...
during the winter. Late spring comes and the cycle repeats.
The queen’s gaster remains contracted for all of the larval-developing stage, reaching no greater than 0.35 mm in diameter. At the onset of spring, she enters physogastry, a phase in which her gaster greatly expands, while the first few larvae show signs of pupation. Her gaster swells with egg-filled ovarioles and grows up to 1.1 mm in diameter. In spite of their size, queens at this stage are very mobile, in contrast to their near motionlessness during the larval-growing stage.
Very soon after physogastry begins, the queen starts laying eggs in a continuous string, with the occasional help of nearby workers. They grab the eggs with their mandibles and gently pull them away from her cloaca
Cloaca
In zoological anatomy, a cloaca is the posterior opening that serves as the only such opening for the intestinal, reproductive, and urinary tracts of certain animal species...
, the orifice of her reproductive tract.
This is only one of many of the workers’ jobs during the egg-laying stage. During this time, workers cease foraging
Foraging
- Definitions and significance of foraging behavior :Foraging is the act of searching for and exploiting food resources. It affects an animal's fitness because it plays an important role in an animal's ability to survive and reproduce...
and migrating to focus on caring for the nest. Workers help larvae get rid of their digestive tracts, a process necessary for pupation, and occasionally eat their feces. They also help them shed their larval skin.
Migration and food cultivation
L. japonica navigate using a trail system marked with a glandExocrine gland
Exocrine glands are a type of ductal glands that secrete their products into ducts that lead directly into the external environment...
secretion from their sternal side, though travel is disorganized and mostly individual. While roughly half of the workers hunts, the other half engages in grooming, larval care, or stands as guards at the edges of the brood pile. The guard ants almost always assume the same position: they face the outside with their anterior end lifted, their forelegs raised, and their mandibles open. Should anything come close, they quickly charge it.
The other half of the workers is occupied with finding, attacking, and paralyzing the species main, if not only, prey, geophilomorph centipedes. Sufficient paralysis can be accomplished with a small number of ants within 10-15 minutes. Most of the time, the workers pull the centipede to the brood pile, with the colony occasionally moving towards the prey as well to meet somewhere in the middle. A few times, however, researchers observed the colony move entirely to the prey site without moving the centipede. During such migrations, workers attached to the larvae’s prothoracic structures to carry them to the paralyzed prey. As previously described, the larvae’s body and mandible shape make for easy feeding. They rip away the outer tissue, and the workers eat from the holes the larvae make.
Predation is active during the larval-growing stage, but stops during the egg-laying stage along with migration. The main source of nutrition during this stage is the larvae themselves.
Larval hemolymph feeding
The queen of L. japonica eats only via larval hemolymph feeding. During the egg-laying stage and physogastry, her rate of LHF doubles. She moves around grabbing all of the larvae in her path, with workers carrying additional larvae to her.The physicality of the queen’s LHF follows. She strokes a mature larva with her antennae
Antenna (biology)
Antennae in biology have historically been paired appendages used for sensing in arthropods. More recently, the term has also been applied to cilium structures present in most cell types of eukaryotes....
, then holds the posterior end with all six legs
Hexapoda
The subphylum Hexapoda constitutes the largest grouping of arthropods and includes the insects as well as three much smaller groups of wingless arthropods: Collembola, Protura, and Diplura . The Collembola are very abundant in terrestrial environments...
, lying on her side and placing her lower mouthparts on the body. She turns the body around, feeling with her mandibles until she finds the “larval hemolymph tap” in the fourth abdominal segment. The lack of lapping movements of the queen’s mouthparts and the lack of larval muscles along the duct organ suggest that the hemolymph is ingested via the queen’s effort. Hemolymph flow would cease by itself when the queen released the larva or by the hemolymph congealing at the opening.
LHF evolved as a less costly form of last-resort nutrition than cannibalism. Many ant species engage in trophic egg
Trophic egg
A trophic egg is an egg which is not laid for reproduction but for nutrition, often for offspring hatched from regular eggs. Trophic eggs are usually unfertilised....
consumption in which the workers have sterile eggs that the ants can feed on. Leptanilla workers, however, do not have ovarioles and thus do not have that option. Because it has never been observed, mouth-to-mouth feeding, or oral trophallaxis
Trophallaxis
Trophallaxis is the transfer of food or other fluids among members of a community through mouth-to-mouth or anus-to-mouth feeding. It is most highly developed in social insects such as ants, termites, wasps and bees. The word was introduced by the entomologist William Morton Wheeler in 1918...
, is thought to be absent from this genus. LHF is seen in Amblyopone and Proceratium, but those genera have much larger populations, ranging from 60,000 to 20,000,000 workers per colony. With so many individuals at the queen’s disposal, severely damaging the larvae she feeds on would have a negligible negative impact on her reproductive fitness. The queens of Leptanilla, on the other hand, cannot afford such a risk with colonies of only 100-200 individuals; an organ reducing the damage of LHF would be highly selected for in such a species. It also allows for the synchronization and cyclical nature of brood development. The absence of trophic eggs, the cost of cannibalism, the specialized predation of sporadic prey, the cyclical and synchronous colony maturation, and the reduced cost of LHF via the “larval hemolymph tap” have all allowed for LHF to become one of this genus’ main feeding habits.