Deer tick or black legged tick (alive) as photographed on a Q-Tip so you can see the size. With ticks this small you might imagine it could be hard to find them on your body or on your scalp under your hair.
I found this crawling on me after I walked around my yard on the grass for about a half hour.
Our experience has been that ticks are active anytime the weather is over 40 degrees including the winter months. They seem most active after a rain. Wet seasons (even a wet January or February) can be prime deer tick time so long as it is over 40 degrees at some point in the day.
Photo taken by ChristineMM on 4/25/11 in Fairfield County, Connecticut (not digitally altered). The color difference is with flash vs. without flash.