Host-seeking activity of adult blacklegged ticks, Ixodes scapularis Say was monitored by flagging during winter months in Beltsville, MD. Ticks were active many days during January and February, the coldest months, with some captures made when there was 70% snow cover and temperatures as low as −2°C. Substantial numbers (70–90 ticks/h of flagging) of adult I. scapularis were captured on favorable days in January and February. The cost to treat white-tailed deer, Odocoileus virginianus (Zimmermann), using ‘4-poster’ deer self-treatment devices, was estimated on a per female tick basis. We estimated deer abundance and tick attachment rates using data from the literature, tick activity levels using weather data and drag counts of ticks, and costs to operate the devices from experience. We found that self-treatment devices need not be operated continuously from late December until the third week of February. On average, savings of half the operating costs would be realized by not operating the devices when tick activity was low.