I found the answer to that question at AntWeb.org, thank you Ben Rubin.
… As I am sure you know, ants, like most insects, don’t do very well in the cold. But ants are always around in the spring when the weather warms up, so how are they surviving the winter? In general, the temperature underground is quite a bit higher than the air temperature. Ants take advantage of this by moving deeper underground in the winter. Some ant nests can be over 15 feet (4.57 meters) below ground level. They can also stay warm by grouping close together and sharing body heat.And ants in places where it is too cold to gather food during the winter may store food in their colonies and fill their crops (an extension of the gut used to store food and water) so that they do not starve.
So generally, ants hibernate during the winter, moving deep underground, grouping together, and generally limiting activity to conserve energy. Ants that live in particularly cold climates, like Leptothorax canadensis from Québec, Canada, and New England, USA, produce their own biological antifreeze so that the water in their bodies does not freeze. These ants are sometimes exposed to temperatures below -20° C (-4° F) but are able to survive even long cold winters by combining all of these methods for staying warm.
– Ben Rubin & the AntAsk Team