Ants: The pioneers of farming and herding

By Dr M.Jayashankar

Humans began domesticating animals more than 10,000 years ago (Neolithic-New stone age) beginning with dogs but the first animals known to have been domesticated as a source of food are sheep in the Middle East. The herding of sheep and goats, or keeping cattle and pigs was to secure a regular supply of fresh meat. Fungus-farming ants figured out farming millions of years before humans, developing their own form of agriculture some 55 million to 60 million years ago. Not only agriculture they are way ahead than us in animal farming and herding!

With a evolutionary history of about 120 million years ants comprise a diverse assemblage of approximately 20,000 species today and have colonized most of the world’s terrestrial landscapes. They impose a strong ecological footprint in many communities in their varied roles as scavengers, predators, granivores, and herbivores.   One of the more striking symbioses is the association between myrmecofauna that is ants and certain insects referred as myrmecophily. Sap is the watery fluid running inside plants and is of two kinds, phloem sap nutrient rich that flows from the leaves (after photosynthesis) bringing sugars to nutrient-hungry parts of the plant, such as the stem and roots. Secondly, xylem consisting mostly of water, mineral elements and nutrients ascending upwards from the roots to the kitchen of the plants- leaves.  Most sap-sucking insects are phloem feeders and some insects feed on xylem sap as well. Phloem and xylem are relatively nutrient-poor compared to the fruit or other vegetative parts of plants, sap-feeding insects with their piercing/sucking mouth parts ingest more water than they need resulting in copious amount of sugary liquid waste called honey dew. The sticky dew spot vehicles parked under infested trees.  Eventually these sticky plants may turn black with a coating of black sooty mold, a type of fungus that grows on the sugars in the drippy droppings of sap-feeders.  This coating of the mold sometimes thickens blocking sun light from penetrating to the leaf impacting photosynthesis. Common sap-feeding insects include mealy bugs, scale insects, aphids, true bugs and whiteflies comprising some of the most destructive pests in agri-horticulture ecosystems.

During a routine observation around the Arunachal Pradesh Regional Centre, ZSI IN Senki valley, Itanagar a symbiotic association involving two species of aphids and one species of mealy bug with four different species of ants was observed. Many ant species have developed a symbiotic relationship with such sap suckers to mutual benefit by herding or farming these insects which provide the ants with sweet honey dew. In return, the ants guard and protect their sap sucking herd from predators. Like alibaba’s ‘open sesame’ utterance, by stroking the back of some aphids with their antennae, the ants can induce a honeydew droplet!. The ants may move the insects to areas on the plants with the best sap prompting the “colonizers” to exponentially explode in population infesting the entire plant in a few weeks. When it rains they may move them to sheltered places, even sometimes into their own nests. Well recent research in ant-aphid relation has revealed that there is high handedness by the boss; ants sometimes clip the wings off aphids to stop them flying away. In addition to sap suckers there are many lycaenid butterfly caterpillars that provide sugary rewards from a special organ called dorsal nectary organ to ants in return for protection from natural enemies. Many of these caterpillars can produce sound to communicate with their guardians. This marriage of convenience enables the myrmecophile to survive and assures the ant mouthful of sugary syrup.

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