Such bite cases began to appear in northern and central Utah in the late 1980’s when the hobo spider was not thought to occur in that state. While still often incorrectly referred to as “brown recluse spider bite”, the systemic effects manifest in these cases are more indicative of hobo spider poisoning (tegenarism) than of brown recluse spider poisoning (Loxosceles). Recently, cases of necrotic arachnidism have begun to appear in several areas adjacent to the previously known range of the hobo spider in the United States and Canada. Finally, in 1983, field studies revealed that the hobo spider was the actual cause of such bites in the northwest, and the spiders’ ability to produce necrotic lesions and systemic illness was demonstrated in the laboratory in 1986 (see Vest (1987) “Necrotic Arachnidism…” and Vest (1987) “Envenomations by…” in references for the original published research. Studies conducted between 19 suggested that another spider was probably the actual agent of these envenomations. In the late 1960’s and early 1970’s physicians in Idaho, Oregon and Washington were presented with cases of probable spider bite that closely resembled bites caused by the brown recluse spider, Loxosceles reclusa. In the United States, however, the hobo spider rapidly adapted to living in urban areas, and without the widespread presence of a dominant competitor, became abundant and began to extend its range by 1968 it had become established as far east as Spokane, Washington and Moscow, Idaho, and as far south as Corvallis, Oregon. The hobo spider is a resident of fields, rarely entering human habitations due to the presence of major competitors, particularly the giant house spider, Tegenaria gigantea, which is a common resident of houses and other man-made structures in Europe thus, human contacts with the hobo spider are uncommon in Europe. Considering the seasonal nature of the hobo spider, it is highly unlikely that a viable breeding population would have developed in the United States based on the occasional introduction of adult or juvenile specimens. It is highly probable that they were transported to and arrived in the Port of Seattle as egg cases attached to wood, etc., rather than as mobile organisms. The means of the spiders’ introduction into the United States was almost certainly commercial shipping vessels carrying cargo originating from agricultural areas of Europe.
The Hobo spider, Tegenaria agrestis, is a moderately large spider of the family Agelenidae which is indigenous to Western Europe that was introduced into the northwestern United States (Port of Seattle) sometime before the 1930’s.
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