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The Hobo Spider
by Nikki Fox

Here's some information on another relatively dangerous spider found in Europe and some parts of the US.

What does it look like?
The hobo spider (Tegenaria agrestis) is a European immigrant that has only recently (1980s) been implicated as a potentially poisonous spider in the United States. Other names used for this spider include the aggressive house spider (although this spider is not usually aggressive) and, less commonly, the Walckenaer spider and the Northwestern brown spider. However, in seeking name stability, the American Arachnological Society has chosen "hobo spider" as the spider's official common name.

While most spiders have 8 eyes, the brown recluse has 6 (3 pairs). The brown recluse spider received its name because of its color and reclusive behavior. Recluse spiders are often colored tan, but can be dark brown to almost white in appearance. These spiders make an irregular and sticky web that is used for shelter rather than for trapping insects. 

Where does it live?
The hobo spider is a member of the spider family Agelenidae, a common group that has many species throughout California and the United States.
Agelenid spiders can have very dense populations in certain habitats. The members of this family construct a snare referred to as a funnel web, which is a trampoline-like, horizontal web constricting back into a funnel or hole. The web is typically found in a crack between bricks or under wood, stones, or vegetation.

The spider waits in the mouth of the funnel for prey to fall onto the horizontal surface, and then it rushes out, grabs the prey, and takes it back to its funnel to consume. If you go outside on a dewy morning, you can often see many of these funnel webs. The hobo spider shares traits with many of its relatives in the Agelenidae family, including coloration and web building characteristics. It is a brown spider about 1/4 to 5/8 inch in body length and lives in a funnel web.

In the United States, this spider lives in the Pacific Northwest from Washington east to Montana and south through Oregon and northern Utah, so it is conceivable that its range may extend into the northernmost areas of California. A survey is currently under way to determine if it is present in northern California. but there have been no documented verifications by a qualified arachnologist (spider specialist) to date.

Hobo spiders are more common further east and are easily found around Salt Lake City, Utah. Interest in this spider has been growing in California because it causes necrotic wounds similar to brown recluse bites, another spider that does not occur in California. Some members of the California medical community have read about the hobo  spider and the effects of its venom and have started to diagnose hobo spider bites without proof of the spider. .

What makes it bite? 
The hobo spider is not naturally an aggressive spider. Most bites occur when a person touches the spider accidentally (if it is hiding in gloves etc) and the spider will bite as a means of self defense. Just be aware of your surroundings and be careful and it will generally leave you alone!

How dangerous is it?
Hobo spiders have been reported to have a bite that can leave a necrotic (i.e., rotting flesh) wound that progresses over several days—similar to that caused by a brown recluse bite. Another reported characteristic symptom of hobo spider bites is a headache that persists for 2 to 7 days and does not abate with analgesics. In its native European habitat, the hobo spider venom is not considered poisonous to humans.

A research study was recently undertaken to compare hobo spider venom from both Pacific Northwest and European hobo spider populations. The venom from both populations was injected into the same strain of rabbits used in the initial research that implicated hobo spiders as potentially poisonous to humans. Neither venom in the study produced necrotic wounds in the rabbits. Although this does not exonerate the hobo spider as a culprit in necrotic wounds, it suggests that more research is needed before the full extent of its poisonous nature is understood.

What can we do to protect ourselves?
In general, removing trash and rubble around the house and sealing windows and door jams will help to reduce the numbers of spiders and other arthropods that can gain access into the home. In the garage (a well known haven for spiders), use spider proof plastic bags to store all gardening apparel (gloves, old shirts, boots) and sports gear (baseball mitts, roller skates) that is used only sporadically. Remember that this will minimize encounters with spiders but not eliminate them completely.

If you do get a necrotic wound in California, you and your medical professional should consider many other common causes to be much more probable than a bite from a hobo spider. If an arthropod is involved at all, one should first consider all those creatures that seek out mammals for blood meals and may cause necrotic-type wounds. These include mites, fleas, bed bugs, soft ticks, hard ticks, cone nose bugs, and kissing bugs.

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