Aestivation is summer's version of hibernation, and snails, frogs and even lemurs do it
Hibernation gets all the attention, but plenty of living things sleep through summer instead. When heat and drought set in, snails glue themselves shut, frogs wrap up in mucus cocoons underground, and daffodils die back to their bulbs. The strategy is called aestivation, from the Latin word for summer, and it is ancient.
Aestivation is a dormancy triggered by high temperatures and dry conditions, marked by inactivity and a slowed metabolism. The fossil record hints that it may have evolved several hundred million years ago. It tends to be a light sleep that can be reversed quickly, yet the physiology closely matches hibernation: the animal must conserve energy and water, ration its reserves, deal with nitrogen waste, and protect its cells by boosting antioxidants and chaperone proteins, sometimes for months or even years.
Plants in Mediterranean climates are classic aestivators. Snowdrops, daffodils and cyclamen grow and flower in the cooler months, then go dormant through the hot, dry summer. Among animals, land snails are the most visible. Many retreat into shade, but others climb crops, trees and fence posts, a habit that has turned some introduced species into farm pests. To stop drying out they seal their shell with a dried mucus membrane; in the Roman snail it is stiffened with calcium carbonate but keeps a tiny hole for air.
Insects and crustaceans join in. Ladybirds, alfalfa weevils and Australia's bogong moths wait out the heat, and one Australian crab spends the dry season underground. Desert tortoises, crocodiles, salamanders, African lungfish and cane toads aestivate too. Australia's water-holding frog buries itself in sand inside a watertight cocoon, carrying a reserve of water in its bladder that Aboriginal people learned to tap in dry country, at the cost of the frog's life.
Mammals rarely do it, but there are exceptions. In 2004 researchers reported in Nature that the fat-tailed dwarf lemur of Madagascar spends seven months of each year dormant inside a tree hole, and four-toed hedgehogs are thought to aestivate through the dry season.
Source: Aestivation
