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How do ticks get onto people?

Ticks Don't trust the washing machine to remove ticks from your clothes. The dryer works better - set for high heat. (Josh Reynolds for The Boston Globe)
June 1, 2009
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How do ticks get onto people? Do they jump, or crawl? If I keep moving, am I safe?

Unlike other bloodsuckers, such as mosquitoes and fleas, ticks can neither fly nor jump. They really just have two ways to get on you. One is to simply drop from a branch. The other is called questing.

Questing is when a tick sits on a blade of grass, a leaf, or a twig, with front-most legs extended. Ticks' legs can detect carbon dioxide from the respiration of a passing animal or person, as well as body heat. If a victim gets close enough and lingers long enough, the tick just crawls on, and then latches on, sticking its hypostosome (a needlelike mouth organ) through the skin.

Once attached (Bela Lugosi accent here, please!) it drinks your blood. So even if you keep moving, it's no guarantee.

Nature has given ticks a strategic advantage. Tick saliva contains anti-inflammatory compounds, so humans are less likely to notice they've been bitten and pull the tick off. Tick saliva also has anticoagulants to help keep the blood flowing. Even more clever, the composition of proteins in tick saliva changes from day to day, making it hard for the body to recognize a coherent threat and get a decent defensive immune reaction going.

Ticks can carry nasty diseases, so be careful, cover up, and use repellent if you go hiking. And at day's end, don't trust a good machine washing to remove all ticks from your clothes; they can often survive laundering.

What does seem to do them in is a long spin-dry with the heat on high.

Dr. Knowledge is written by physicist John Swain of Northeastern University. E-mail questions to drknowledge@globe.com or write Dr. Knowledge, c/o The Boston Globe, PO Box 55819, Boston, MA 02205-5819.