Myrmecophily
Encyclopedia
Myrmecophily is the term applied to positive interspecies associations between ant
s and a variety of other organisms such as plants, arthropods, and fungi. Myrmecophily refers to mutualistic associations with ants, though in its more general use the term may also refer to commensal
or even parasitic interactions.
The term myrmecophile, is used mainly for animals that associate with ants. There are an estimated 10,000 species of ants (Formicidae), with a higher diversity
in the tropics. In most terrestrial ecosystems ants are ecologically and numerically dominant, being the main invertebrate predators. As a result, ants play a key role in controlling arthropod richness, abundance, and community structure. There is evidence that the evolution of myrmecophilous interactions has contributed to the abundance and ecological success of ants, by ensuring a dependable and energy-rich food supply and thus providing a competitive advantage for ants over other invertebrate predators. Most myrmecophilous associations are opportunistic, unspecialized, and facultative (meaning both species are capable of surviving without the interaction), though obligate mutualisms (those in which one or both species are dependent on the interaction for survival) have also been observed for many species.
s.
Myrmecophiles may have various roles in their host ant colony. Many consume waste materials in the nests, such as dead ants, dead larvae, or fungi
growing in the nest. Some myrmecophiles, however, feed on the stored food supplies of ants, and a few are predatory on ant eggs, larvae, or pupae. Others benefit the ants by providing a food source for them. Many myrmecophilous relationships are obligate, meaning one or the other participant requires the relationship for survival. Some associations are facultative, benefiting one or both participants but not being necessary to their survival.
Myrmecophilous associations are best known in butterflies of the family Lycaenidae
. Many lycaenid caterpillars produce nectar by specialized organs and communicate with the ants through sound and vibrations. The association with ants is believed to reduce the parasitisation of the butterfly caterpillars.
There are myrmecophilous beetles in the families Coccinellidae
(e.g. the ladybird Thalassa saginata), Aphodiidae, Scarabaeidae
, Lucanidae, Cholevidae, Pselaphidae, Staphylinidae, Histeridae and Ptiliidae
. Myrmecophilous associations are also seen in various other insects such as aphid
s and treehopper
s, as well as the hoverfly
genus Microdon
and several other groups of flies.
Some mites and spiders are also myrmecophilous, particularly some oribatid mites, which have been found to be obligate myrmecophiles.
Others myrmecophile groups include
The first major work in cataloguing British
myrmecophiles was done by Horace Donisthorpe
in his 1927 book The Guests of British Ants.
, and Orchidaceae
. In general, myrmecophytes (or ant plants) usually provide some form of shelter and food in exchange for ant “tending,” which may include protection, seed dispersal (see myrmecochory
), reduced competition from other plants, hygienic services, and/or nutrient supplementation.
Three of the most common and important structural adaptations of ant plants are the domatia
, Beltian bodies
and extrafloral nectaries. Plant domatia are pre-formed nesting sites provided by the plant in the form of hollowed out stems, petioles, thorns, or curled leaves. The production of ant-specialized domatia has been documented in over 100 genera of tropical plants. Beltian bodies provide a high-energy food source to ants in the form of nutritive corpuscles produced on leaflet tips , and they have been described in at least 20 plant families. Extrafloral nectaries (EFN’s) are known to occur in at least 66 families of angiosperm plants in both temperate and tropical regions, as well as some ferns, but are absent in all gymnosperms and are most abundant in the topics. EFN's being outside of the plant flowers are not employed in pollination; their primary purpose is to attract and sustain tending ants. Many plants can control the flow of nectar from the EFN’s so that the availability of nectar varies according to daily and seasonal cycles. Because ants can respond quickly to changes in flow rate from EFN’s, this may be possible mechanism by which plants can induce greater ant activity during times of peak herbivory and minimize overall costs of nectar production. The combined nutritional output of EFN’s and Beltian bodies is a significant food source for tending ants, and in some cases can provide the total nutritive needs for an ant colony.
In exchange for nesting sites and food resources, ants protect plants from herbivore
s. Perhaps the best-known example of ant-plant mutualism is in bullhorn acacias (Acacia cornigera
) and their tending Pseudomyrmex
ants in African savanna
s. This system was studied extensively by Dan Janzen in the late 1960’s, who provided some of the first experimental evidence that ants significantly reduce herbivory rates of myrmecophytes,,D. Janzen, “Interaction of the bull's-horn acacia (Acacia cornigera L. ) with an ant inhabitant (Pseudomyrmex ferruginea F. Smith) in Eastern Mexico,” Univ. Kansas Sci. Bull. , vol. 47, 1967, pp. 315-558. and since then may other studies have demonstrated similar results in other systems as well. In exchange for protection, the acacias provide domatia, Beltian bodies, and EFN’s, and there is evidence that the Pseudomyrmex ants can survive exclusively on these food resources without having to forage elsewhere. For many plants, including the bullhorn acacias, ants can significantly reduce herbivory from both phytophagous insects as well as larger organisms, such as large grazing mammals. Obligately associated ant species are some of most aggressive ants in the world, and can defend a plant against herbivory by large mammals by repeatedly biting their attacker and spraying formic acid into the wound.
Myrmecophily is considered a form of indirect plant defense against herbivory, though ants often provide other services in addition to protection. Some ants provide hygienic services to keep leaf surfaces clean and deter disease, and defense against fungal pathogens has also been demonstrated. It is common for ants to prune epiphytes, vines, and parasitic plants from their host plant, and they sometimes thin the shoots of neighboring plants as well. In doing so, ants reduce plant-plant competition for space, light, nutrients, and water. Finally, current work focusing on ants’ role in nutrient supplementation for plants has shown that in many ant-plant relationships nutrient flow is bidirectional. One study has estimated that while 80% of the carbon in the bodies of Azteca spp. workers is supplied by the host tree (Cecropia spp.), 90% of the Cecropia tree’s nitrogen was supplied by ant debris carried to the tree as a result of external foraging. In light of these services, myrmecophily can be very advantageous in ensuring a plant’s survival and ecological success.
butterfly caterpillar
s and hemipterans. Forty-one percent of all ant genera include species that associate with insects. In all ant-insect associations the ants provide some service in exchange for nutrients in the form of honeydew, a sugary fluid excreted by many phytophagous insects. Interactions between honeydew-producing insects and ants is often called trophobiosis, a term which merges notions of trophic relationships with symbioses between ants and insects. This term has been criticized, however, on the basis that myrmecophilous interactions are often more complex than simple trophic interactions, and the use of symbiosis is inappropriate for describing interactions among free-living organisms.
Some of the most well-studied myrmecophilous interactions involve ants and hemipterans (earlier grouped in the order Homoptera which included the Auchenorrhyncha
and Sternorrhyncha
), especially aphid
s. There are around 4000 described species of aphids, and they are the most abundant myrmecophilous organisms in the northern temperate zones. Aphids feed on the phloem sap of plants, and as they feed they excrete honeydew droplets from their anus. The tending ants ingest these honeydew droplets then return to their nest to regurgitate the fluid for their nestmates (see trophallaxis
). Between 90-95% of the dry weight of aphid honeydew is various sugars, while the remaining matter includes vitamins, minerals, and amino acids. Aphid honeydew can provide an abundant food source for ants (aphids in the genus Tuberolachnus can secrete more honeydew droplets per hour than their body weight) and for some ants aphids may be their only source of food. In these circumstances, ants may supplement their honeydew intake by preying on the aphids once the aphid populations have reached certain densities. In this way ants can gain extra protein and ensure efficient resource extraction by maintaining honeydew flow rates that do not exceed the ants’ collection capabilities. Even with some predation by ants, aphid colonies can reach larger densities with tending ants than colonies than without. Ants have been observed to tend large “herds” of aphids, protecting them from predators and parasitoids. Aphid species that are associated with ants often have reduced structural and behavioral defense mechanisms, and are less able to defend themselves from attack than aphid species that are not associated with ants.
Ants engage in associations with other honeydew-producing hemipterans such as scale insects (Coccidae), mealybugs (Pseudococcidae), and treehoppers (Membracidae), and most of these interaction are facultative and opportunistic with some cases of obligate associations, such as hemipterans that are inquiline
, meaning they can only survive inside ant nests. In addition to protection, ants may provide other services in exchange for hemipteran honeydew. Some ants bring hemipteran larvae into the ant nests and rear them along with their own ant brood. Additionally, ants may actively aid in hemipteran dispersal: queen ants have been observed transporting aphids during their dispersive flights to establish a new colony, and worker ants will often carry aphids to a new nesting site if the previous ant nest has been disturbed. Ants may also carry hemipterans to different parts of a plant or to different plants in order to ensure a fresh food source and/or adequate protection for the herd.
Myrmecophily among lycaenid caterpillars differs from the associations of hemipterans because caterpillars feed on plant tissues, not phloem sap, and therefore do not continually excrete honeydew. Caterpillars of lycaenid butterflies have therefore evolved specialized organs that secrete chemicals to feed and appease ants. Because caterpillars do not automatically pass honeydew, they must be stimulated to secrete droplets and do so in response to ant antennation, which is the drumming or stroking of the caterpillar’s body by the ants’ antennae. Some caterpillars possess specialized receptors that allow them to distinguish between ant antennation and contact from predators and parasites, and others produce acoustic signals that agitate ants, making them more active and likely better defenders of the larvae. As with homopteran myrmecophiles, ants protect Lycaenid larvae from predatory insects (including other ants) and parasitoid wasps, which lay their eggs in the bodies of many species of Lepidoptera larvae. The enemy-free space that ants can provide for lycaenids is significant: one study conducted by Pierce and colleagues in Colorado experimentally demonstrated that survival rates of G. lygdymus larvae declined 85-90% when ant partners were excluded. These interactions do not come without an energetic cost to the butterfly, however, and it has been shown that ant-tended individuals reach smaller adult sizes than non-tended individuals due to the costs of appeasing ants during the larval stage. Interactions with ants are not limited to the butterfly’s larval stage, and in fact ants can be important partners for butterflies at all stages of their life cycle. For example, adult females of many lycaenid butterflies preferentially oviposit on plants where ant partners are present, possibly by using ants’ own chemical cues in order to locate sites where juvenile butterflies will likely be tended by ants. Finally, while ant attendance has been most widely documented in Lycaenid butterflies (and to some extent riodinid butterflies), many other lepidopteran species are known to associate with ants, including many moths.
In studying the coevolution of myrmecophilous organisms, many researchers have addressed the relative costs and benefits of mutualistic interactions, which can vary drastically according to local species composition and abundance, variation in nutrient requirements and availability, host plant quality, presence of alternative food sources, abundance and composition of predator and parasitoid species, and abiotic conditions. Because of the large amounts of variation in some of these factors, the mechanisms that support the stable persistence of myrmecophily are still unknown. In many cases, variation in external factors can result in interactions that shift along a continuum of mutualism, commensalism, and even parasitism. In almost all mutualisms, the relative costs and benefits of interactions are asymmetrical; that is, one partner experiences greater benefits and/or fewer costs than the other partner. This asymmetry leads to “cheating,” in which one partner evolves strategies to receive benefits without providing services in return. As with many other mutualisms, cheating has evolved in interactions between ants and their partners. For example, some lycaenid larvae are taken into ant nests where they predate on ant brood and offer no services to the ants. Other lycaenids may parasitize ant-plant relationships by feeding on plants that are tended by ants, apparently immune to ant attack because of their own appeasing secretions. Hemipterophagous lycaenids engage in a similar form of parasitism in ant-hemipteran associations. In light of the variability in outcomes of mutualistic interactions, and also the evolution of cheating in many systems, much remains to be learned about the mechanisms that maintain mutualism as an evolutionarily stable interaction.
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...
s and a variety of other organisms such as plants, arthropods, and fungi. Myrmecophily refers to mutualistic associations with ants, though in its more general use the term may also refer to commensal
Commensalism
In ecology, commensalism is a class of relationship between two organisms where one organism benefits but the other is neutral...
or even parasitic interactions.
The term myrmecophile, is used mainly for animals that associate with ants. There are an estimated 10,000 species of ants (Formicidae), with a higher diversity
Biodiversity
Biodiversity is the degree of variation of life forms within a given ecosystem, biome, or an entire planet. Biodiversity is a measure of the health of ecosystems. Biodiversity is in part a function of climate. In terrestrial habitats, tropical regions are typically rich whereas polar regions...
in the tropics. In most terrestrial ecosystems ants are ecologically and numerically dominant, being the main invertebrate predators. As a result, ants play a key role in controlling arthropod richness, abundance, and community structure. There is evidence that the evolution of myrmecophilous interactions has contributed to the abundance and ecological success of ants, by ensuring a dependable and energy-rich food supply and thus providing a competitive advantage for ants over other invertebrate predators. Most myrmecophilous associations are opportunistic, unspecialized, and facultative (meaning both species are capable of surviving without the interaction), though obligate mutualisms (those in which one or both species are dependent on the interaction for survival) have also been observed for many species.
Myrmecophile
A myrmecophile is an organism that lives in association with antAnt
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...
s.
Myrmecophiles may have various roles in their host ant colony. Many consume waste materials in the nests, such as dead ants, dead larvae, or fungi
Fungus
A fungus is a member of a large group of eukaryotic organisms that includes microorganisms such as yeasts and molds , as well as the more familiar mushrooms. These organisms are classified as a kingdom, Fungi, which is separate from plants, animals, and bacteria...
growing in the nest. Some myrmecophiles, however, feed on the stored food supplies of ants, and a few are predatory on ant eggs, larvae, or pupae. Others benefit the ants by providing a food source for them. Many myrmecophilous relationships are obligate, meaning one or the other participant requires the relationship for survival. Some associations are facultative, benefiting one or both participants but not being necessary to their survival.
Myrmecophilous associations are best known in butterflies of the family Lycaenidae
Lycaenidae
The Lycaenidae are the second-largest family of butterflies, with about 6000 species worldwide, whose members are also called gossamer-winged butterflies...
. Many lycaenid caterpillars produce nectar by specialized organs and communicate with the ants through sound and vibrations. The association with ants is believed to reduce the parasitisation of the butterfly caterpillars.
There are myrmecophilous beetles in the families Coccinellidae
Coccinellidae
Coccinellidae is a family of beetles, known variously as ladybirds , or ladybugs . Scientists increasingly prefer the names ladybird beetles or lady beetles as these insects are not true bugs...
(e.g. the ladybird Thalassa saginata), Aphodiidae, Scarabaeidae
Scarabaeidae
The family Scarabaeidae as currently defined consists of over 30,000 species of beetles worldwide. The species in this large family are often called scarabs or scarab beetles. The classification of this family is fairly unstable, with numerous competing theories, and new proposals appearing quite...
, Lucanidae, Cholevidae, Pselaphidae, Staphylinidae, Histeridae and Ptiliidae
Ptiliidae
Ptiliidae is a family of very tiny beetles with a worldwide distribution. This family contains the smallest of all beetles, with a length of 0.5 mm, and even the largest members of the family do not exceed 2 mm. The weight is approximately 0.4 milligrams....
. Myrmecophilous associations are also seen in various other insects such as aphid
Aphid
Aphids, also known as plant lice and in Britain and the Commonwealth as greenflies, blackflies or whiteflies, are small sap sucking insects, and members of the superfamily Aphidoidea. Aphids are among the most destructive insect pests on cultivated plants in temperate regions...
s and treehopper
Treehopper
Treehoppers and thorn bugs are members of the family Membracidae, a group of insects related to the cicadas and the leafhoppers. There are about 3,200 known species of treehoppers in over 600 genera...
s, as well as the hoverfly
Hoverfly
Hoverflies, sometimes called flower flies or syrphid flies, make up the insect family Syrphidae. As their common name suggests, they are often seen hovering or nectaring at flowers; the adults of many species feed mainly on nectar and pollen, while the larvae eat a wide range of foods...
genus Microdon
Microdon
Hover flies of the genus Microdon are unusual among the Diptera. Like other members of the subfamily, they are myrmecophiles, meaning they inhabit the nests of ants...
and several other groups of flies.
Some mites and spiders are also myrmecophilous, particularly some oribatid mites, which have been found to be obligate myrmecophiles.
Others myrmecophile groups include
- OrthopteraOrthopteraOrthoptera is an order of insects with paurometabolous or incomplete metamorphosis, including the grasshoppers, crickets and locusts.Many insects in this order produce sound by rubbing their wings against each other or their legs, the wings or legs containing rows of corrugated bumps...
, like the cricketCricket (insect)Crickets, family Gryllidae , are insects somewhat related to grasshoppers, and more closely related to katydids or bush crickets . They have somewhat flattened bodies and long antennae. There are about 900 species of crickets...
Myrmecophilus acervorumMyrmecophilus acervorumMyrmecophilus acervorum is an orthopteran insect belonging to the family Myrmecophilidae . This continental European species is probably the most widespread and most frequently encountered member of this rather obscure family found in Europe... - DipteraDipteraDiptera , or true flies, is the order of insects possessing only a single pair of wings on the mesothorax; the metathorax bears a pair of drumstick like structures called the halteres, the remnants of the hind wings. It is a large order, containing an estimated 240,000 species, although under half...
, like the stratiomyidStratiomyidaeThe soldier flies , are a family of flies . The family contains about 1,500 species in about 400 genera worldwide. Adults are found near larval habitats...
fly Clitellaria obtusa - Molluscs, like Allopeas myrmekophilos
The first major work in cataloguing British
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
myrmecophiles was done by Horace Donisthorpe
Horace Donisthorpe
Horace St. John Kelly Donisthorpe was an eccentric British myrmecologist and coleopterist, memorable in part for his enthusiastic championing of the renaming of the genus Lasius after him as Donisthorpea, and for his many claims of discovering new species of beetles and ants.He is often considered...
in his 1927 book The Guests of British Ants.
Ant-plant interactions
Ant-plant interactions are geographically widespread, with hundreds of species of myrmecophytic plants in several families including the Leguminosae, EuphorbiaceaeEuphorbiaceae
Euphorbiaceae, the Spurge family are a large family of flowering plants with 300 genera and around 7,500 species. Most are herbs, but some, especially in the tropics, are also shrubs or trees. Some are succulent and resemble cacti....
, and Orchidaceae
Orchidaceae
The Orchidaceae, commonly referred to as the orchid family, is a morphologically diverse and widespread family of monocots in the order Asparagales. Along with the Asteraceae, it is one of the two largest families of flowering plants, with between 21,950 and 26,049 currently accepted species,...
. In general, myrmecophytes (or ant plants) usually provide some form of shelter and food in exchange for ant “tending,” which may include protection, seed dispersal (see myrmecochory
Myrmecochory
Myrmecochory is seed dispersal by ants, an ecologically significant ant-plant interaction with worldwide distribution. Myrmecochorous plants produce seeds with elaiosomes, a term encompassing various external appendages or "food bodies" rich in lipids, amino acid, or other nutrients that are...
), reduced competition from other plants, hygienic services, and/or nutrient supplementation.
Three of the most common and important structural adaptations of ant plants are the domatia
Domatia
Domatia are tiny chambers produced by plants that house arthropods.Domatia differ from galls in that they are produced by the plant rather than being induced by their inhabitants...
, Beltian bodies
Beltian body
A Beltian body is a structure found on the leaves of some species of Acacia. Beltian bodies, named after Thomas Belt, are found on the tips of each leaflet and are rich in lipids and proteins and often red in colour. They are believed to have evolved in a symbiotic relationship with ants...
and extrafloral nectaries. Plant domatia are pre-formed nesting sites provided by the plant in the form of hollowed out stems, petioles, thorns, or curled leaves. The production of ant-specialized domatia has been documented in over 100 genera of tropical plants. Beltian bodies provide a high-energy food source to ants in the form of nutritive corpuscles produced on leaflet tips , and they have been described in at least 20 plant families. Extrafloral nectaries (EFN’s) are known to occur in at least 66 families of angiosperm plants in both temperate and tropical regions, as well as some ferns, but are absent in all gymnosperms and are most abundant in the topics. EFN's being outside of the plant flowers are not employed in pollination; their primary purpose is to attract and sustain tending ants. Many plants can control the flow of nectar from the EFN’s so that the availability of nectar varies according to daily and seasonal cycles. Because ants can respond quickly to changes in flow rate from EFN’s, this may be possible mechanism by which plants can induce greater ant activity during times of peak herbivory and minimize overall costs of nectar production. The combined nutritional output of EFN’s and Beltian bodies is a significant food source for tending ants, and in some cases can provide the total nutritive needs for an ant colony.
In exchange for nesting sites and food resources, ants protect plants from herbivore
Herbivore
Herbivores are organisms that are anatomically and physiologically adapted to eat plant-based foods. Herbivory is a form of consumption in which an organism principally eats autotrophs such as plants, algae and photosynthesizing bacteria. More generally, organisms that feed on autotrophs in...
s. Perhaps the best-known example of ant-plant mutualism is in bullhorn acacias (Acacia cornigera
Acacia cornigera
Acacia cornigera, commonly known as Bullhorn Acacia , is a swollen-thorn acacia native to Mexico and Central America. The common name of "bullhorn" refers to the enlarged, hollowed-out, swollen thorns that occur in pairs at the base of leaves, and resemble the horns of a steer...
) and their tending Pseudomyrmex
Pseudomyrmex
Pseudomyrmex is a genus of stinging, wasp-like ants in the family Formicidae . They are large eyed, slender ants with an arboreal habitat. They are found exclusively in the New World in tropical and subtropical regions...
ants in African savanna
Savanna
A savanna, or savannah, is a grassland ecosystem characterized by the trees being sufficiently small or widely spaced so that the canopy does not close. The open canopy allows sufficient light to reach the ground to support an unbroken herbaceous layer consisting primarily of C4 grasses.Some...
s. This system was studied extensively by Dan Janzen in the late 1960’s, who provided some of the first experimental evidence that ants significantly reduce herbivory rates of myrmecophytes,,D. Janzen, “Interaction of the bull's-horn acacia (Acacia cornigera L. ) with an ant inhabitant (Pseudomyrmex ferruginea F. Smith) in Eastern Mexico,” Univ. Kansas Sci. Bull. , vol. 47, 1967, pp. 315-558. and since then may other studies have demonstrated similar results in other systems as well. In exchange for protection, the acacias provide domatia, Beltian bodies, and EFN’s, and there is evidence that the Pseudomyrmex ants can survive exclusively on these food resources without having to forage elsewhere. For many plants, including the bullhorn acacias, ants can significantly reduce herbivory from both phytophagous insects as well as larger organisms, such as large grazing mammals. Obligately associated ant species are some of most aggressive ants in the world, and can defend a plant against herbivory by large mammals by repeatedly biting their attacker and spraying formic acid into the wound.
Myrmecophily is considered a form of indirect plant defense against herbivory, though ants often provide other services in addition to protection. Some ants provide hygienic services to keep leaf surfaces clean and deter disease, and defense against fungal pathogens has also been demonstrated. It is common for ants to prune epiphytes, vines, and parasitic plants from their host plant, and they sometimes thin the shoots of neighboring plants as well. In doing so, ants reduce plant-plant competition for space, light, nutrients, and water. Finally, current work focusing on ants’ role in nutrient supplementation for plants has shown that in many ant-plant relationships nutrient flow is bidirectional. One study has estimated that while 80% of the carbon in the bodies of Azteca spp. workers is supplied by the host tree (Cecropia spp.), 90% of the Cecropia tree’s nitrogen was supplied by ant debris carried to the tree as a result of external foraging. In light of these services, myrmecophily can be very advantageous in ensuring a plant’s survival and ecological success.
Ant-insect interactions
Ants tend a wide variety of insect species, most notably lycaenidLycaenidae
The Lycaenidae are the second-largest family of butterflies, with about 6000 species worldwide, whose members are also called gossamer-winged butterflies...
butterfly caterpillar
Caterpillar
Caterpillars are the larval form of members of the order Lepidoptera . They are mostly herbivorous in food habit, although some species are insectivorous. Caterpillars are voracious feeders and many of them are considered to be pests in agriculture...
s and hemipterans. Forty-one percent of all ant genera include species that associate with insects. In all ant-insect associations the ants provide some service in exchange for nutrients in the form of honeydew, a sugary fluid excreted by many phytophagous insects. Interactions between honeydew-producing insects and ants is often called trophobiosis, a term which merges notions of trophic relationships with symbioses between ants and insects. This term has been criticized, however, on the basis that myrmecophilous interactions are often more complex than simple trophic interactions, and the use of symbiosis is inappropriate for describing interactions among free-living organisms.
Hemiptera
Auchenorrhyncha
The Auchenorrhyncha is the suborder of the Hemiptera which contains most of the familiar members of what was called the Homoptera - groups such as cicadas, leafhoppers, treehoppers, planthoppers, and spittlebugs. The aphids and scale insects are the other well-known "Homoptera", and they are in...
and Sternorrhyncha
Sternorrhyncha
Sternorrhyncha is a suborder of the Hemiptera which contains the aphids, whiteflies, and scale insects, groups which were traditionally included in the order Homoptera. "Sternorrhyncha" refers to the rearward position of the mouthparts relative to the head...
), especially aphid
Aphid
Aphids, also known as plant lice and in Britain and the Commonwealth as greenflies, blackflies or whiteflies, are small sap sucking insects, and members of the superfamily Aphidoidea. Aphids are among the most destructive insect pests on cultivated plants in temperate regions...
s. There are around 4000 described species of aphids, and they are the most abundant myrmecophilous organisms in the northern temperate zones. Aphids feed on the phloem sap of plants, and as they feed they excrete honeydew droplets from their anus. The tending ants ingest these honeydew droplets then return to their nest to regurgitate the fluid for their nestmates (see 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...
). Between 90-95% of the dry weight of aphid honeydew is various sugars, while the remaining matter includes vitamins, minerals, and amino acids. Aphid honeydew can provide an abundant food source for ants (aphids in the genus Tuberolachnus can secrete more honeydew droplets per hour than their body weight) and for some ants aphids may be their only source of food. In these circumstances, ants may supplement their honeydew intake by preying on the aphids once the aphid populations have reached certain densities. In this way ants can gain extra protein and ensure efficient resource extraction by maintaining honeydew flow rates that do not exceed the ants’ collection capabilities. Even with some predation by ants, aphid colonies can reach larger densities with tending ants than colonies than without. Ants have been observed to tend large “herds” of aphids, protecting them from predators and parasitoids. Aphid species that are associated with ants often have reduced structural and behavioral defense mechanisms, and are less able to defend themselves from attack than aphid species that are not associated with ants.
Ants engage in associations with other honeydew-producing hemipterans such as scale insects (Coccidae), mealybugs (Pseudococcidae), and treehoppers (Membracidae), and most of these interaction are facultative and opportunistic with some cases of obligate associations, such as hemipterans that are inquiline
Inquiline
In zoology, an inquiline is an animal that lives commensally in the nest, burrow, or dwelling place of an animal of another species. For example, some organisms such as insects may live in the homes of gophers and feed on debris, fungi, roots, etc...
, meaning they can only survive inside ant nests. In addition to protection, ants may provide other services in exchange for hemipteran honeydew. Some ants bring hemipteran larvae into the ant nests and rear them along with their own ant brood. Additionally, ants may actively aid in hemipteran dispersal: queen ants have been observed transporting aphids during their dispersive flights to establish a new colony, and worker ants will often carry aphids to a new nesting site if the previous ant nest has been disturbed. Ants may also carry hemipterans to different parts of a plant or to different plants in order to ensure a fresh food source and/or adequate protection for the herd.
Lycaenid butterflies
Multiple levels of myrmecophily
Many trophobiotic ants can simultaneously maintain associations with multiple species. Ants that interact with myrmecophilous insects and myrmecophytes are highly associated: species that are adapted to interact with one of these myrmecophiles may switch among them depending on resource availability and quality. Of the ant genera that include species that associate with ant plants, 94% also include species that associate with trophobionts. In contrast, ants that are adapted to cultivate fungus (leaf cutter ants, tribe Attini) do not possess the morphological or behavioral adaptations to switch to trophobiotic partners. Many ant mutualists can exploit these multi-species interactions to maximize the benefits of myrmecophily. For example, some plants will host aphids instead of investing in EFN’s, which may be more energetically costly depending on local food availability. The presence of multiple interactors can strongly influence the outcomes of myrmecophily, often in unexpected ways.Significance of myrmecophily in ecology
Mutualisms are geographically ubiquitous, found in all organismic kingdoms, and play a major role in all ecosystems. Combined with the fact that ants are one of the most dominant lifeforms on earth, it is clear that myrmecophily plays a significant role in the evolution and ecology of diverse organisms, and in the community structure of many terrestrial ecosystems.Evolution of positive interactions
Questions of how and why species coevolve are of great interest and significance. In many myrmecophilous organisms it is clear that ant associations have been influential in the ecological success, diversity, and persistence of species. Analyses of phylogenetic information for myrmecophilous organisms as well as ant lineages have demonstrated that myrmecophily has arisen independently in most groups multiple times. Because there have been multiple gains (and perhaps losses) of myrmecophilous adaptations, the evolutionary sequence of events in most lineages is unknown. Exactly how these associations evolve also remains unclear.In studying the coevolution of myrmecophilous organisms, many researchers have addressed the relative costs and benefits of mutualistic interactions, which can vary drastically according to local species composition and abundance, variation in nutrient requirements and availability, host plant quality, presence of alternative food sources, abundance and composition of predator and parasitoid species, and abiotic conditions. Because of the large amounts of variation in some of these factors, the mechanisms that support the stable persistence of myrmecophily are still unknown. In many cases, variation in external factors can result in interactions that shift along a continuum of mutualism, commensalism, and even parasitism. In almost all mutualisms, the relative costs and benefits of interactions are asymmetrical; that is, one partner experiences greater benefits and/or fewer costs than the other partner. This asymmetry leads to “cheating,” in which one partner evolves strategies to receive benefits without providing services in return. As with many other mutualisms, cheating has evolved in interactions between ants and their partners. For example, some lycaenid larvae are taken into ant nests where they predate on ant brood and offer no services to the ants. Other lycaenids may parasitize ant-plant relationships by feeding on plants that are tended by ants, apparently immune to ant attack because of their own appeasing secretions. Hemipterophagous lycaenids engage in a similar form of parasitism in ant-hemipteran associations. In light of the variability in outcomes of mutualistic interactions, and also the evolution of cheating in many systems, much remains to be learned about the mechanisms that maintain mutualism as an evolutionarily stable interaction.