Animals with chemosynthetic symbionts

Most animals feed on plants or other animals, and humans are no exception. Unlike our ancestors, we rely on others to produce our food. This raises a question: why can’t we simply grow our own food or carry a backpack of plants to harvest when hungry?

Some animals and protists actually host microbes that act as a “living backpack,” converting CO₂ and small organic molecules into biomass using chemical energy, much like plants use sunlight. The host then consumes this microbial “harvest” while keeping conditions favorable for growth.

So why don’t more animals live this way? Because such systems only work where chemical energy is abundant, and most animals need far more food than they could ever carry. For example, feeding one human requires about 0.7 hectares of farmland—the size of a soccer field. Thinking about these microbial strategies helps us reflect on our own place as food consumers in a world of finite resources.