By: Rick
In the late 19th century in the United States, spiders were not considered to be causes of medical concern. At that point, the black widow gained notoriety for causing severe medical problems.
It wasn’t until 1957 that the brown recluse spider in North America was proven dangerous. In the 1970s and 1980s, the yellow sac spider and the hobo spider become tagged as creatures that could cause lesions similar to mild brown recluse spider bites.
With black widows and brown recluses, the body of research and reports of medical case histories strongly supported their nasty reputations.
However, the yellow sac and hobo spiders were implicated more from circumstantial evidence. Recent research has questioned the conventional wisdom that these latter two spiders are actually medically important because of discrepancies in the toxicology information surrounding them.
The Yellow Sac Spider
The yellow sac spider is a generic-looking creature with no real defining characteristics that would allow a non-arachnologist to identify the spider correctly just by looking at it in a vial. In general, it is a medium-sized spider (about 3/8-inch in body length) with an abdomen that is longer than wide. The coloration is often yellow or yellowish but can vary somewhat depending on what the spider has been eating. It has eight eyes in two rows of four, which are readily visible with a hand lens. Often the ends of its legs are darkened so it looks like it has blackish socks.
Sac spiders get their names from the habit of creating a retreat by curling a leaf or wedging themselves in a crevice in tree bark and spinning a little refugia of silk. The sac serves to protect the spider against weather and acts as an early warning system for predatory intruders.
There are only two species of yellow sac spiders in the United States, both of the genus Cheiracanthium. The native species, C. inclusum, is considered mostly an agrarian spider found in the vegetation of farm crops. The non-native species, C. mildei, originated from Europe, was not found in the United States until the 1950s, and like many creatures who become liberated in a new environment, they have spread throughout the country. Unlike the native species, which is found most frequently outdoors, the European spider is very common inside homes and, therefore, interacts with humans more often. It is a common urban spider.
These spiders would happily be going about their own business unbeknownst to humans except that in the 1970s in North America and 1980s in South Africa, publications implicated yellow sac spiders as the cause of mild rotting flesh skin lesions.
This occurred at a time when it was acceptable to use circumstantial evidence to place blame on spiders because it was so difficult to amass a sufficent number of verified cases where the spider was captured in the act of biting and properly identified. However, what this led to instead was the incorrect fingering of yellow sac spiders as culprits in skin lesions. This information was readily repeated in medical textbooks and was considered fact by many professions, including the pest management industry.
However, a study in 2006 with verified bites showed that no necrosis and only minor, self-healing symptoms occur.
This is not to say that yellow sac spiders are innocent creatures. They do have a strong tendency to bite humans and seem to do so with little provocation. As with most spiders, yellow sac spider bites typically occur as a last-chance defensive response to being squeezed between human flesh and another object.
The bite is usually intensely painful, like that of a bee sting, so it gets one’s attention (they have awakened sleeping bite victims). In comparison, bites by widow or recluse spiders are described as being just like a pinprick and barely perceptible. However, the typical symptoms of yellow sac spider bites include slight redness at the site, slight swelling and itchiness. Then all symptoms disappear within 2 or 3 days. In some cases, there was recurring itching for a few weeks.
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