Summary. A category of ice nucleators associated with the cullular matrix is described for the first time. The nucleators are active in warm acclimatized Rhagium inquisitor beetles, causing the beetles to suffer lethal freezing following cooling to -8°C. They are also present in winter but do not express nucleating potential and thereby allow the insects to survive cold exposure by means of extensive supercooling ability. Expression of their nucleating activity is not inhibited beyond colligative effects by glycerol or by thermal hysteresis antifreezes.