When the temperature starts to drop below +5 Celsius (+41 Ferenhiet), ants become sluggish and retreat to their nests.
They will huddle together to stay warm and eventually move deeper and deeper underground (in their nests) as the temperature drops.
Source: 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.
Ants that live in particularly cold climates … produce their own biological antifreeze so that the water in their bodies does not freeze.