The Marin/Sonoma Mosquito and Vector Control District is warning residents to take precautions while playing in the outdoors this winter, as ticks are out en force. The western black-legged tick, also called a deer tick, is most active from fall through early spring (the nymphs, or juveniles, are most active in the spring and summer). Tick bites can transmit the bacterium that causes Lyme disease, named after the town in Connecticut where it was discovered in the 1970s, as well as other infectious diseases. Lyme can begin with mild flu-like symptoms but, if left untreated, may develop over time into serious chronic health problems affecting many bodily systems. The district this week urged people to watch for ticks in grassy, brushy or wooded areas and noted that, contrary to popular belief, ticks do not jump, fly or fall out of trees. Rather, adult ticks wait with legs outstretched on the tips of vegetation for passersby. The most common ways a person becomes a host is by sitting on a log or leaning against a tree, followed by walking or sitting in leaf litter, research shows. Ticks can remain on their hosts for hours and even days, with the risk of infection growing with the length of time they remain attached. In Sonoma and Marin Counties, the district estimates that 3 to 5 percent of adult ticks carry the Lyme bacterium. Officials suggest that hikers where light-colored clothing, long sleeves and pants, apply repellent containing DEET to exposed areas, shower after exposure and remove attached ticks properly—using fine-tipped tweezers applied close to the skin’s surface to steadily pull the insect out, and then washing well.