Freeze Avoidance Many insects and other small animals have perfected methods for staying liquid even at very low subzero temperatures. Most insects that winter under the snow in the leaf litter can cool to least -10 to -15·C before they freeze whereas those that winter above the snow pack can often cool to -40·C without freezing. Arctic insects can do even better, some staying liquid down to -55·C. How do they do this? Goldenrod Gall Moth (Epiblema scudderiana) Caterpillar - This caterpillar produces a narrow elliptical gall on goldenrod stems. It avoids freezing and stays liquid in extreme cold. The freeze avoidance strategy has three main parts. First, special antifreeze proteins are produced and circulated in the blood. These proteins are specially designed so that they bind to the surface of embryonic ice crystals and prevent them from growing any further. So, any ice that forms stays in tiny crystals that can't do any harm to tissues. Antifreeze proteins are also present in the blood of cold water marine fish so that they will not freeze when they swim in -2·C polar waters. Secondly, the animals build up extremely high concentrations of sugars or sugar alcohols in their blood and tissues and this lowers the freezing point of their body water. This is exactly the same strategy that we use to prevent the water in a car radiator from freezing and indeed, some insects actually synthesize and accumulate the same chemical, ethylene glycol, that we put in the car! More commonly, however, a related chemical called glycerol is used which is much less toxic. By midwinter, the amount of glycerol in an insect's body is so high that it often makes up 20-25% of its entire body weight! The third part of the freeze avoidance strategy is to prevent contact with molecules that can act as "ice nucleators", molecules that "seed" the formation of ice in body fluids. Ice itself is the most potent ice nucleator and so animals take steps to avoid contact with environmental ice. Some insects do this by wintering in very dry places, but most rely on wrapping themselves in water-proofing. This can be done by increasing the thickness of the waxy cuticle on an insect's body or by spinning a water-proof cocoon. Potential nucleators inside the insect's body are also eliminated such as by emptying the gut to get rid of foreign particles and bacteria and by seasonal changes to the types of proteins present in their blood to remove any whose structure could stimulate ice crystallization.