The Relationships of Ants with other Creatures
Some creatures rely on ants for their own survival. The relationship between the ants and their dependents can be mutual, harmful or one-sided.
Symbiosis in ants. What is it?
Many people consider ants to be a pest, an unwanted presence in the garden or home. However, there are many types of creatures that welcome ants and indeed depend on ants for their survival. This can be either a mutual partnership, where both ants and dependents mutually benefit, or it can be one-sided where one or the other is the sole beneficiary. This article looks at some of these relationships. It will concentrate mainly on the relationships of ants with other insects.
Symbiosis in ants: Mutualism
Aphids are the bane of many a gardener. These “greenfly” attach themselves to various planets, such as rose bushes. On closer inspection of these aphids, you will notice one thing: ants walking among the aphids. Some would assume that the ants are eating the aphids, but a more detailed inspection would show that these ants are not harming the aphids at all. The ants use the aphids as a source of indirect food. Indirect in that the ants are not eating the aphids. The ants are eating something that the aphids produce, namely, honeydew. As gross as it sounds, this honeydew is the excrement of the aphid. However, it is not as one may assume. Honeydew is a nutritious, sweet, clear, or milky substance. Ants consider it to be a delicacy.
The aphid bores into the plant’s stem, tapping into the reservoir of the natural sap of the plant. Usually, this enters the aphid’s digestive system by force, due to the sap being under pressure, rather than by the aphid actively sucking the sap. As the sap passes through the aphid’s body, certain substances are removed, i.e., those needed for the aphid’s own nutritional needs. Waste by-products are added, and the result “honeydew” is excreted out. As mentioned earlier, ants find this honeydew very appealing. Ants are often seen among the aphids, licking up this nutritional exudate.
Myrmecophily. What is the benefit for the aphids?
What about the aphids? How do they benefit from this attention from the ants? Various creatures feed on aphids, such as the ladybirds. Being out in the open on the plant stems, aphids are very prone to be eaten by such predators. This is where the ants come in. The ants defend and protect the aphids from their enemies, driving them away, or killing them. Ants may take the corpses of the predator into their nests for the larvae. If the predator, such as the ladybird, lays eggs near the aphids, which would result in the emergent larvae attacking and eating them. The ants will remove such eggs and larvae.
There are some species of aphid who have lost the ability to expel the honeydew from their bodies, and therefore the ants can help with this. Some species of ants may even take aphids into their nests during the chilly winter months. This type of symbiosis is often termed mutualism, as both organisms receive help from the other.
Symbiosis in ants: Parasitism
Elsewhere on this website, I have discussed the methods by which one species of ant parasitises another species of ant, usually to the benefit of the parasitic species, but to the detriment of the host. Here, however, I will discuss species of insect other than ants that use ants as a host for their parasitic methods.
Mites (Acarina), are often found in ant nests, or even on the bodies of the ants themselves. Lasius ants, at least those found in the UK, may play host to the Cillibano comata. The mites cling onto the ants, normally the gaster, in characteristic positions, that is, one on each side of the gaster. The mite penetrates the cuticle (hard armour-like external covering) with their mouthpiece and suck the blood, or, rather, the haemolymph, of the ant.
Roundworms (Nematoda) live inside some ants. An example of this is the species Pelodera janeti which enters the mouth of the ant, finding its way into the pharyngeal gland. Here it feeds on the oils within the gland. Once its larval stage is complete it leaves the ant, living within the soil and detritus of the ant’s nest. Another type of roundworm that can infect ants, Mermis, lives inside the gaster of female ants. It is a large organism that once it reaches a certain stage of its development within the ant’s body. Later it will emerge from the ant, fatally damaging the ant in the process. This parasite prevents the normal growth of wings in the developing queen ant, it understood.
Symbiosis in ants: Commensalism
This is a type of symbiosis where one organism benefits from another, with the other, neither helped nor harmed. Various insects make their home within ant nests, even without an invitation. Platyarthrus hoffmannseggii is a small white woodlouse which lives in the nests of various species of ants, such as Lasius niger, L. flavus and some Myrmica species. The woodlouse feeds on ant droppings and mildew. It appears to depend on the ants for its survival as it is not seen living outside of ant nests, other than when it may follow ants to aphid “farms”.
It could be argued that the ants benefit from this and therefore should be classed as mutualism. However, I regard this relationship as commensal as even though the woodlice are cleaning up the ant nests, the ants would have removed the detritus themselves. This is clear from the fact that not every ant nest of this species has these woodlice in them. In other words, though the woodlice are doing the ants a service by carrying out a task that the ants would normally do, the ants do not depend on the woodlice for their survival.
Another commensal species is Forcellinia wasmanni. This mite lives amongst the rubbish/detritus dump within ant nests, eating the waste material. The mite attaches to the ant, feeding from greases on the ant’s body. They may even steal food as one ant feeds another via trophallaxis. However, though the ants tolerate these mites, if one is found in the brood chamber, they are often killed. Usually Forcellinia is not a problem for the ants, however, a particularly heavy infestation can harm the whole colony.
Another mite, Lelaps myrmecophila, feeds on the larvae of the Forcellina, keeping their population in check.
Symbiosis in ants: Anting
There is another type of creature that uses ants for its own benefit, without harming the ants. Birds. One group of bird species, Passerines, use ants for grooming purposes. The birds stand amongst certain species of ants and allow the ants to crawl over their bodies. The bird picks up an ant and places it in amongst its feathers, usually under the wings. Two things happen here: the ants remove any mites from the bird’s body, or the annoyed ant squirts formic acid onto the bird’s feathers. The formic acid has the effect of an insecticide, thereby ridding the bird of annoying mites and ticks. Passerine birds only use certain species of ants for this purpose, such as those of the Formicine genus as they use formic acid. Myrmica ants have a sting, and as a result, are not used by the birds for this purpose.
There are many other species of arthropods, insects and other creatures that use ants in either of the three symbiotic methods described above. Symbiosis in ants is a fascinating subject.
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