Stanford Medicine Newsletter Updates For the Local Community


Creature discomforts

Beware the bites and stings of the great outdoors


Consider the yellow jacket. The ornery, covetous yellow jacket. That turkey sandwich you were eating at a table outside your workplace? That’s hers now. If you have the nerve to try to reclaim your lunch, you might pay a painful price.

But wasps are just one of several stinging or biting critters that can trip up a beautiful summer day in the Bay Area: There are also mosquitoes, rattlesnakes, ticks and jellyfish.

Luckily, Stanford Hospital & Clinics has perhaps the foremost concentration of wilderness medicine physicians in the nation, including emergency medicine physician Paul Auerbach, MD, who with a team of experts wrote the definitive book on the subject, the roughly 2,300-page Wilderness Medicine (now in its sixth edition). It covers virtually everything that could give you trouble outdoors: bear attacks, sprains, altitude sickness, drowning, lightning, sunburn, heatstroke, volcanic eruptions—you name it.

Those looking for something lighter can turn to Auerbach’s paperback, Medicine for the Outdoors, which, at a little more than 500 pages, covers much of the important ground. Both books were consulted for this article, as were Auerbach himself and fellow Stanford wilderness medicine experts Robert Norris, MD, chief of emergency medicine, and Grant Lipman, MD, an emergency medicine physician and adventure rae medical expert.



With the warm weather comes one of the season’s more ubiquitous pests: the mosquito. To foil these bloodsucking arthropods, there are essentially two preventive measures you can take: a physical barrier or insect repellent, or both, Auerbach said. “Wear something that covers your arms and legs,” he said. “Light-colored clothing is less attractive to mosquitoes. Insect repellent, especially one with DEET (N,N-Diethyl-meta-toluamide), is quite effective.”

Worse than its itchy bite, however, is the insect’s potential as a vector for infectious disease, such as West Nile virus. About 20 percent of people infected with the virus will develop flulike symptoms in three to 14 days. Less than 1 percent of those infected suffer more serious health problems, such as encephalitis or meningitis. (In 2011, there were 158 reported cases of West Nile virus among people in California and nine reported fatalities, according to the state Department of Public Health.)


Unlike mosquitoes, jellyfish are not interested in preying on you. People are stung by these brainless, gelatinous sea animals when they accidentally brush against them or try to handle them. Luckily, species off the California coast are likely to inflict only mild or moderate pain, if any, Auerbach said. The Portuguese man-of-war is rarely sighted in Northern California waters.

If you know you’re going to be sharing the water with jellyfish, wear a wetsuit or synthetic-nylon dive skin, and give jellies wide berth, he said. Do not touch jellyfish in the water or on the beach.
A bluish jellyfish-like creature, the by-the-wind sailor (Velella velella), often washes up on West Coast beaches in large numbers during the spring and early summer, Auerbach noted. People sometimes confuse these small, plankton-eating hydrozoa—usually measuring only a few inches in width—with the much larger man-of-war. Although velella are considered mostly harmless to humans, Auerbach advised against touching them, which could cause skin irritation.



“They would much rather be left alone, given the chance,” Norris said, referring to northern Pacific rattlesnakes, Northern California’s only native species of venomous snake.

An internationally recognized expert on venomous snake bites, Norris said that the Bay Area has a healthy population of these pit vipers. They are generally active from April through September but will sometimes emerge from hibernating in places like rodent holes, crevices and rock piles on warm winter or late-autumn days to sun themselves. “They are not deep hibernators,” Norris said.

You can find them in grasslands, in the woods, on hiking trails—“really, just about anywhere,” Norris said. “I’ve seen some patients who were bitten in Palo Alto; one was in her garden when it happened.”

If a rattlesnake crosses your path, give it the right of way. If it’s not moving, you can walk around it, making sure to stay at least several feet away, he said. The good news is that these snakes are not aggressive: If they feel threatened, they will generally try to slither away or give their infamous warning rattle (be aware that some snakes may have lost their rattles or not yet grown them). Their venom is fairly toxic, but very few people actually die from bites. Annually, there are some 8,000 venomous snake bites nationwide, resulting in only about six deaths.

To prevent bites, look where you’re putting your feet and hands. Wear hiking shoes and long pants, Norris said. “Be alert, and don’t step over logs,” he added. “If you’re going through tall grass, use a walking stick to probe in front of you. The snake will often let you know it’s there.”



Unlike the rattlesnake, the tick, another denizen of the California wilderness, has an incentive to bite you: Your blood could make for a satisfying meal. There are roughly a half-dozen tick species in California that will attach themselves to humans, but it’s the western blacklegged tick that is the most notorious; it is a known vector for Lyme disease, the most common tick-borne disease in the state.

Immature ticks, known as nymphs, are about the size of a poppy seed, and they’re the most likely to be carrying the disease-causing bacteria. They like to hang out among leaves and fir needles on woodland floors. They also will climb up on logs and on the lower trunks and branches of trees. Adult ticks, which are less likely to carry the bacteria, prefer to sit on grasses and on bushes, waiting to latch on to prey.

When hiking in woodlands, grasslands or chaparral, or along hillside trails, wear light-colored clothes that cover your arms and legs, and tuck pants into socks, Norris advised. Check your clothes and exposed parts of your body, including your scalp, for ticks every few hours. Insect repellents with DEET are effective deterrents, he added.

Yellow jackets


Yellow jackets are social wasps, sometimes confused with honeybees, and they typically become a problem for picnickers and other al fresco diners beginning in August.

“Cover your food and keep a tight lid on trash cans,” Lipman advised. Don’t swat at the wasps; this can make them angry. Unlike bees, they are able to sting repeatedly, he added. Avoid crushing them, which releases a pheromone that acts as a kind of chemical alarm and may encourage other nearby wasps to attack. Steer clear of their nests, commonly found in rodent burrows, wall cavities, attics and old tree stumps, and under eaves.

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