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Introduction to ants and symbiosis
Long before mankind even existed, ants were advanced farmers. Through cooperation and symbiosis, ants can extract maximum nutrition from their surroundings. They milk aphids, grow fungus and care for other nutritive plants.
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In total contrast to the ants’ otherwise aggressive behaviours there is also a soft side these insects. Where ants are found, one can also see their symbiosis and cooperation with nature. Ants are experts at getting the most out of their environment and uses both insects and plants for the task.
Ants and aphids
When discussing ants and their cooperation with other life forms, their relationship of aphids quickly pops up. For millions of years, ants have farmed the land, both by means of agriculture as well as animal husbandry. Many ant colonies live a life close to colonies of aphids, whom they protect as farmers would protect their own herds.
In exchange for protection, the aphids exudes a secretion that the ants love called honeydew. The liquid is very attractive in the world of insects, as well as being highly nutritious. It all works like this: when the ant closes up on the aphid, it gently taps it with an antenna or front leg. When feeling this tap, the aphid secrets its liquid – payment for its protection. The glands are located by the anus, emitting the liquid which is then absorbed by the ant. The ant moves from aphid to aphid, gathering ”taxes” up until eventually returning to the colony with the supplies. (1)
The aphid itself gets nutrition from sucking liquids from the current host plant. This provides the necessary proteins, vitamins, minerals and carbohydrates needed. Half of the nutrition is consumed while half is saved to serve as honeydew for the herders.
Aphids and ants communicate with pheromones
Researchers have shown that ants and aphids share some parts of a chemical language – the system which ants base their communications on (read more: How Ants Communicate). For example, the ants ”mark” their herds with their colony scent. So, just like humans, ants mark their belongings. If a colony of aphids is under attack, they can emit a scent-cocktail telling their host to come to their aid. The scent also makes other aphids let go of their hold of the plant and fall down from it. A way of escaping the battlefield if no ants come to their rescue. It is worth noting that all sorts of aphids do not behave like this, and this is simply an example of the symbiosis between specific species. (2)
When comparing ”domesticated” aphids with wild ones, one can spot a genetical difference. The ones protected by the ants are much less prone to survive attacks on their own. Their self defence is not as good, and they lack essential parts such as special legs to jump away. This is a clear example of how evolution, through symbiosis, have specialised a species via social structures
The Lasius family and aphids symbiosis
The yellow meadow ant (Lasius flavus) has an intimate relationship with aphids. The species seldom travels above the surface, which can be concluded by looking at their small eyes, in comparison to other Lasius-species. They do not need to see very much, since they spend most of their lives in darkness. The flavus ants therefore make use of root louses. A sort of aphid living in the ground on the plant roots.
Both the black garden ant and the yellow meadow ant can bring home aphid eggs or herds of aphids to the colony. This is to keep them there, safe, during the winter season. In spring, they are placed on suitable pastures and are moved around until the ants have located the perfect spots (3). The species of Lasius neoniger treats aphids as any other member of the colony, and their eggs are cared for the same way as the ant eggs. (4)
Ants and plants in symbiosis
Ants do not only cooperate with other insects. They can also form a symbiosis with different plants. The Indian plant of Nepenthes bicalcarata is a plant that feeds on insects falling down into its mouth. In other words: an insectivorous plant. In spite of this, whole colonies of ants can live in its cavities. How?
Just like with aphids, ants provide the plant with protection – mostly from herbivores. In exchange for this, the ants are provided with a safe place to live (with the exception of the risk of being eaten in their home), and with some of the plant’s prey. There are hundreds of interesting ant-plant symbiosis described from 150 years of research (5). Ants has become the perfect lodgers of the plant-houses. They protect it from enemies, distributes its seeds and cares for its roots in the form of dirt and nutrition. In exchange, plants can produce nectar of different kind, perfect for the ants.
It is general knowledge in the myrmecology department that ants can protect plants from other insects and pests. But what is not really confirmed is that ants can protect plants from animals as big as cows, horses of humans. This has been observed, but there is not enough scientifically data to prove it – yet. An example of this is a worker of the species of Pseudomyrmex (America) that can smell large mammals and, with the rest of the workers, runs out of the plant to defend it. When compared to a non-protected plant the result is thrilling. The plants with ant inhabitants get on much better than the ones without. The latter must fight pests, insects and mammals all on their own (6). This proves that a symbiosis with ants might be something to think about.
1. Bert Holldobler & Edward O. Wilson (1995) “Journey to the ants” p. 143
2. Bert Holldobler & Edward O. Wilson (1990) “The Ants” p. 522-523
3. Per Douwes, Johan Abenius, Björn Cederberg, Urban Wahlstedt (2012) Nationalnyckeln “Steklar: Myror-getingar. Hymenoptera: Formicidae-Vespidae” p. 43 (Swedish)
4. Bert Holldobler & Edward O. Wilson (1990) “The Ants” p. 527
5. Bert Holldobler & Edward O. Wilson (1990) “The Ants” p. 530
6. Bert Holldobler & Edward O. Wilson (1990) “The Ants” p. 532