The risk of contracting tick-borne disease from deer tick nymphs and adults varies by . Although deer ticks are inactive in freezing temperatures, and survive well under the snow, they may be seeking a host (an animal to feed on) in bare sunny spots in midwinter.

from http://www.ticksinmaine.com/risk/seasons
http://www.ticksinmaine.com/risk/uploads/images/layout/LifeCycle-x350.jpg