The pine processionary caterpillar and its cousin, the oak processionary caterpillar, look harmless enough, but the hairs that cover their bodies contain a toxin that can cause a serious allergic reaction. Add to that the fact that those hairs can sail right off the caterpillar like dandelion seeds, and you have an airborne allergen not unlike pollen.
"I think most people, when they think of anaphylaxis or allergic reactions, they're thinking about insects like wasps and bees," said John Klotz, an entomologist at the University of California, Riverside. But these caterpillars exemplify the range of creatures out there that don't need to sting you to cause a reaction.
Klotz is publishing a review of reports on dozens of animals and insects, including the hairy caterpillars, that can cause a severe allergic response.
"I thought it would be a good way of heightening awareness of the problem," he said.
Deemed as forest pests in Europe, the processionary caterpillars -- named as such because they form long lines when heading into or out of their nests -- have been implicated in numerous individual and group incidents.
In June 2004, more than 40 people who were sitting under an infested oak tree in the region of Saarland in Southwest Germany were sickened by the caterpillars although only a few actually touched them.
"Someone could inhale them [the hairs] or ingest them, and in some cases they could penetrate the skin," said Klotz. Some children have been hospitalized after eating the creatures. "A lot of times they'll pick up something furry and curious like a caterpillar, and you know, sometimes ingest them, just out of curiosity."
You've probably heard of indoor allergens such as mold or dust mites, but what about the Asian ladybug? In recent years researchers have pegged the beetles as a source of allergic symptoms including hay fever, coughing, wheezing and watery eyes.
Asian ladybugs, formally known as multicolored Asian lady beetles, were introduced to the U.S. as early as 1916 to control the aphid population, but the beetles don't like the cold, so they regularly swarm into houses when the temperature drops.
"These things come in in the winter, and you have real trouble," said Dr. Thomas Platts-Mills, professor of medicine, allergy and clinical immunology at the University of Virginia. "And they actually bite, occasionally."
Indoor clusters can number in the thousands. Beginning in the late 1980s, homeowners began to report large indoor swarms in Louisiana.
The beetles are now well-established along the East Coast, in parts of the Midwest, and the Southeast. They look similar to North American ladybugs but vary in color from yellow to brown and scarlet, with polka-dots optional.
Allergy experts such as Platts-Mills refer to the Asian ladybug as a "new seasonal indoor allergen."
The best advice for preventing an Asian ladybug infestation is to seal the cracks and crevices in your home that could let them in, said Donald Lewis, professor of entomology at Iowa State University.
Once they're inside, Lewis suggests: "You can spray them to kill them, but you might as well use your vacuum cleaner to suck them up."