An insect has been trapped in my side table for almost two years. It makes "grinding" noises occasionally, but how is it surviving without water?

This insect could be a number of species depending on where you are located, but I think you are actually interested in how it survives without water. This is a really interesting question.

Several animals, including insects and certain small mammals, can survive indefinitely without access to water by creating their own H2O through the metabolism of carbohydrates. Most stuff that grows is basically made of carbohydrates, that is, molecules consisting of a chain of carbon and hydrogen atoms. There are many carbohydrates with many different configurations of the chain. The chain may contain other elements but basically every carbohydrate chain consists essentially of long or short sequences of carbon and hydrogen atoms.

Wheat, eaten by mice, is basically made up of long and complex carbohydrate chains. Petrol, burned up in your car, is made up of shorter carbohydrate chains. In both cases, when these chains are metabolised, or oxydised, the carbon pairs up with two oxygen to make carbon dioxide CO2 and wanders off to contaminate the atmosphere and be a greenhouse gas while two hydrogen atoms pair up with one oxygen atom to make water, H2O. Incredible as it may seem, that water is sufficient to satisfy the water needs of certain specialised insects and small mammals.

In other words, these animals, including the ones grinding away in your furniture, can survive without water by manufacturing water out of carbohydrates. Your furniture is made of wood, which means that it is made of carbohydrates, like your pasta. The hydrogen incorporated in your furniture is being converted to water by your little friends, while your furniture gently outgasses carbon dioxide to warm the planet.

If you are stuck in a desert and dying of thirst, don’t think that you are going to solve your problem by eating bread, you need a highly specialised metabolism to capture and make use of the water that will be created, you can just look at the loaf and think, “This thing can be converted into water and save my life, if only my body knew how.”