UPSC Prelims 2022 Q90: Fungus-Farming Organisms — Explained
Certain species of which one of the following organisms are well known as cultivators of fungi?
- Ant
- Cockroach
- Crab
- Spider
Answer: (a) Ant
Statement-wise explanation
- a: correct — Fungus-growing (attine) ants of the Americas farm fungi as their main food. There are more than 230 described species, found from the United States to Argentina. Leafcutter ants of the genera Atta and Acromyrmex cut fresh leaves and use them to feed gardens of the fungus Leucoagaricus gongylophorus. The ants eat swollen hyphal tips called gongylidia, and this fungus cannot live outside their nests. Ant farming began about 50 million years ago.
- b: incorrect — Cockroaches are not known to farm fungi. This option is a trap because termites, which do farm fungi, are now classified inside the cockroach order Blattodea. But the farmers are only the termite subfamily Macrotermitinae, which grows Termitomyces fungi in Africa and Asia. Ordinary cockroaches do not farm.
- c: incorrect — Crabs are crustaceans that scavenge, filter-feed or graze. No crab is known for cultivating fungi. The best-studied fungus farmers are all insects: ants, termites and ambrosia beetles.
- d: incorrect — Spiders are arachnids, and almost all of them are predators that catch live prey. They do not cultivate fungi. Fungi are more relevant to spiders as parasites that infect them.
How to eliminate
This is mostly a fact-recall question. The fact to remember is that the classic fungus farmers are insects: ants, termites and ambrosia beetles. That rules out crab and spider straight away. Crabs are crustaceans, and spiders are predatory arachnids that eat live prey, not anything grown. Of the two insects, the cockroach is the trap. A candidate who has read that termites farm fungi, and that termites are close relatives of cockroaches, may pick it. Remember that only some termites farm, and cockroaches do not. The question's wording also helps: 'certain species… well known' points to a famous example. Leafcutter ants are the best-known farmers in the animal world outside humans.
Know more
Insect agriculture (fungiculture)
Humans began farming about 10,000 years ago. Some insects began tens of millions of years earlier. Three insect lineages grow fungi for food. They plant it, feed it, weed out pests and pass it on to new colonies.
| Farmer | Where | Fungus grown | What they feed it | Origin |
|---|---|---|---|---|
| Attine ants (incl. leafcutters Atta, Acromyrmex) | Americas, mainly Neotropics | Leucoagaricus gongylophorus and relatives | Fresh leaves, plant debris | ~50 million years ago |
| Macrotermitine termites | Africa and Asia (incl. India, e.g. Odontotermes) | Termitomyces | Plant matter passed through the gut, built into 'fungus combs' | ~31 million years ago |
| Ambrosia beetles | Worldwide, in wood | Various ambrosia fungi | Wood of tunnels they bore | Several separate origins |
How ant farming works
- Workers cut leaves but do not eat them. They chew them into a pulp that feeds the fungus garden.
- The fungus breaks down plant tissue the ants cannot digest. The ants then eat its nutrient-rich hyphal tips (gongylidia).
- Gardens are attacked by a parasitic fungus, Escovopsis. The ants carry Pseudonocardia bacteria on their bodies, and these bacteria make antifungal compounds that protect the garden.
- 'Higher' attine fungi depend fully on the ants, much like domesticated crops.
Why it matters
- The fungus combs in termite mounds act as an 'external rumen' that breaks down lignin and cellulose. This recycles nutrients in tropical soils.
- Termitomyces mushrooms that grow out of termite mounds are gathered and eaten in parts of India and Africa.
- These partnerships are textbook cases of mutualism, a relationship where both partners gain.