Using mainly the overwintering prepupae of a “ slug caterpiller ”, Cnidocampa flavescens (Walk.), the mechanism for the frost-resistance in insects was investigated.
Though the freezing point of the blood shows the value of about −2°C. the prepupae are very readily supercooled. When cooled below −20°C., however, the insect body suddenly congeals hard. Insects frozen thus, even for a long period of 100 days, usually withstand the solidification of their bodies without any harmful effect upon either the further development or upon the next generation.
Judging from the shape of the freezing curves of the prepupae and the freezing processes of the blood and isolated tissues, it is inferred that the most probable freezing process of the caterpillar is as follows. At first, the blood freezes rapidly, and consequently the grade of supercooling of the tissue cells is very much lessened by the latent heat of fusion of ice. Extra-cellular freezing of the tissue cells then takes place, in which case the properties of the blood as well as some property of the plasmic surface layer of the cells may play an important role in the prevention of the transmission of freezing into the cell. With the advance of the blood freezing, the tissue cells undergo dehydration and contraction; neverthless, they usually withstand such a condition for a long period, provided that the freezing temperature is not too low. Consequently, the so-called anabiotic state of a frozen insect does not necessarily mean the destruction of the cell structure.