When you think about it, animals are weird. They ignore the abundant source of energy above their heads – the sun – and choose instead to invest vast amounts of energy in cumbersome equipment for eating and digesting food. Why don't they do what plants do, and get their energy straight from sunlight?

The short answer is that many do. Corals are animals but have algae living in them that use sunlight to make sugar. Many other animals, from sponges tosea slugs, pull the same trick. One species of hornet can convert sunlight into electricity. There are also suggestions that aphids can harness sunlight, although most biologists are unconvinced.

But all these creatures are only distantly related to us. No backboned animal has been found that can harness the sun – until now. It has long been suspected, and now there is hard evidence: the spotted salamander is solar-powered.

Plants make food using photosynthesis, absorbing light to power a chemical reaction that converts carbon dioxide and water into glucose and releases oxygen. Corals profit from this reaction by housing photosynthetic algae inside their shells.

Long-term partners

Spotted salamanders, too, are in a long-term relationship with photosynthetic algae. In 1888, biologist Henry Orr reported that their eggs often contain single-celled green algae called Oophila amblystomatis. The salamanders lay the eggs in pools of water, and the algae colonise them within hours.