As mammals travel, the fruits eventually fall off or are freed from fur when animals groom themselves. If the fruits land in suitable spots, the seeds inside germinate, and a new plant generation grows and produces a new crop of aggravating, sticky fruits.
Humans, however, aren't so helpful in transporting such fruits to ideal growing grounds. When we groom ourselves after a hike, these fruits usually wind up in linty piles in parking lots or in a trash can by the washing machine.
I know of one instance, however, when this method of seed dispersal did potentially favor a plant species. In September 2001, I was with a group of biologists exploring a rare Missouri sand prairie. At lunch, we discovered that we had inadvertently collected a good number of fruits of an imperiled species of sticktight, Desmodium strictum, on our pants. Alarmed that we had unwittingly carted off a large portion of the species' seed crop, we picked them off our clothes and collected them in an empty French fry envelope, to be later broadcast over the sand prairie by one of the biologists.
If you don't want to serve as a vehicle for seed dispersal, there are a few precautions you can take. Try wearing sturdy nylon fabric, to which many seeds can not adhere. You might invest in a pair of gaiters made of heavy duty nylon that you can slip over your pants and the tops of your shoes. These will keep your socks, shoelaces and lower pant legs seed-free. Corduroy garments seem to attract fewer sticky seeds than denim. Fleece jackets and pullovers are like sticktight magnets. You'll be digging them out of your outerwear all fall and winter. Pocket combs and butter knives are helpful in scraping seeds off clothing.
Could an outing be complete without getting our hats or jackets hung up on thorny catbrier vines, or pulling blackberry or dewberry brambles from our pant legs? Thorns, spines and prickles - the defense system of many plants - deter many animals from eating plants, but they also benefit many animals. In "The Book of Forest and Thicket," John Eastman writes that vines in the genus Smilax - known by such colorful names as greenbrier, catbrier, blasphemy vine and tramps' troubles - are like "flexible rolls of vegetative barbed-wire." A thicket of greenbrier or blackberry can be impenetrable to humans