A prairie rattlesnake basks in the morning sun at the door of its den, formerly the abode of prairie-dogs. Click on its tail to hear the "little bell."
Meanwhile, Clark and the rest of the Corps were working their way upriver. Clark complained,
The previous Fourth of July, in 1804, at Independence Creek near today's Kansas City, Kansas, Clark reported that "a Snake bit Jo: Fields on the side of the foot which Swelled much." Captain Lewis quickly applied a poultice of "Barks" to the wound. That would have been powdered "Peruvian Bark," from the South American cinchona tree. It contains quinine, which would have been effective on malarial fevers, but was useless in any form against rattlesnake venom.
How serious might Field's injury have been? Laurence Klauber has summarized the symptoms of the bite of a C. viridis viridis:
there is an immediate sensation like the sting of a wasp; there is little or no bleeding; a spreading feeling of numbness, especially at the tongue and lips; the tips of the fingers and toes tingle; there is a tendency to faint, and thereafter to remain in a coma for some time; nausea and vomiting are usually present; swelling begins about ten minutes after the bite, with discoloration, and continues with severe pain for thirty-six to forty-eight hours.2
Fortunately, although a rattlesnake bite is traumatic to both body and mind, it is seldom fatal to humans, but merely achieves just what the biter intends: It distracts and immobilizes a creature considered to be a threat to its safety. Five days after Field's encounter, Sergeant Gass announced, "the man that was snake bitten is become well."
Rattlesnake sightings and encounters, which began near the Manitou River in Missouri, were evidently too numerous to count, but the men killed at least seventeen before the expedition was over. There were several close calls, too. Lewis "trod within five inches" of one near the Judith River in Montana on May 26, 1805,
Another close call occurred on June twelfth, when one of the men cordelling a canoe "cought one by the head in Catch'g hold of a bush on which his head lay reclined."
On July eleventh, at the canoe-building camp upriver from Great Falls, a rattler struck at Private Whitehouse's leg, but hit only his legging. "I shot it," the soldier reported, "it was 4 feet 2 Inches long, and 5 Inches and a half around." A month later, in the vicinity of the Gates of the Mountains, Private Whitehouse reported that
It's hard to tell, from these reports just how much danger any man was in. The striking distance of a prairie rattler varies according to several factors, including the species, its position relative to its prey, and how excited it happens to be at the instant of the strike. The principal determinant may be the reptile's length, for according to Laurence Klauber, a rattler's strike will rarely extend more than half its length, measured from the front of the anchor coil. Unfortunately, it .s difficult to estimate the actual length of any reptile without counting its ventral scales, and doing that to a snake-on-the-hoof is definitely unwise.
Equally important is the speed of the strike. In a series of tests using artificial prey, an adult prairie rattlesnake struck with an average speed of 8.12 feet per second—slower than a prizefighter's punch.3