Hobo spiders
Hobo spiders (Tegenaria Agrestis) were introduced into north-western USA1 from Europe by commercial vessels carrying agricultural products. They were probably introduced during the early 1900 to the port of Seattle, and have since then spread to the states surrounding Washington, which is Oregon, Idaho and Nevada, Montana and Utah.
Appearance
The Hobo spider is a hairy spider with hairy legs and cephalothorax. Males have two pedipalps that are enlarged at the top which makes them appear similar to boxing gloves. It is 1½-2 inch or 4-5 cm in diameter. In the section about identification (further down) you can read what to look for to find out if the spider you are studying is a Hobo spider.
Note. Not a Hobo Spider but an Aggressive House Spider. |
Funnel-web spiders
They are member of the funnel-web weaver spider family Agelenidae. Funnel-web spiders can move rapidly, and the Hobo spider should be capable of running at a velocity of almost 4 feet per second. It produces a flat web with a funnel like lair in the middle, where the spider is located waiting for prey.
Misconception about Hobo spiders
Many people believe that Hobo spiders are extremely dangerous. Fortunately, all evidence suggests that this requires more scientific scrutiny to be confirmed. Indeed, a Hobo spider bite may be dangerous - the scientific community just needs further proof. Such proof can only emerge if people capture the spider that bit them and brings it with them to the hospital.
Hobo spider geographic distribution
The Hobo spider can be found in Oregon, Idaho, (Wyoming2), Montana, Utah, Washington and Southern British Columbia in Canada. Its nature makes it uncomfortable in very dry regions, so encountering a Hobo spider south of Utah is probably impossible.
Hobo spider identification
Giant house spiders and many other spiders are often misidentified as Hobo spiders. However, there are a number of characteristics that can help determine whether a spider is a Hobo or not. Unfortunately, some of these identification characteristics require a microscope as neither size nor color can be used as identification parameters.
Here are the few characteristics you can look after to exclude that a given spider is a Hobo:
- If you can see dark rings around the spiders leg it is not a Hobo spider.
- If its legs are shiny and misses fine hair it is not a Hobo spider.
- If its palp are long and pointed it is not a Hobo spider.
- If it has stripes on its cephalothorax it is not a Hobo spider.
Note: The cephalothorax is the first part of the spider’s body where the legs are attached.
For an exact identification it is necessary to study reproductive structures under a microscope.
Hobo spider bites
Hobo spider bites have been linked to necrotic arachnidism and systemic poisoning. However, uncertainty exists to how well documented the link between necrotic arachnidism and the Hobo spider really is. Has it been Hobo spiders in all cases?
In a study by Darwin K. Vest (1987)3 giant rabbits were subjected to forced Hobo spider bites. The rabbits were followed to study how their lesions evolved and their organs were investigated subsequently. The study showed that male Hobo spiders caused both dermal lesions and organ haemorrhage while female bites mainly caused dermal lesions. In this study, however, only a few rabbits were tested.
Necrotic arachnidism
Consequences, or sufferings, due to poisoning by a Hobo spider are called tegenarism; the name is related to the name tegenaria. Tegenarism is probably the leading cause of spider envenomations in north-western USA and Canada, as e.g. black widows are not abundant that far north. The effects of Hobo spider’s bites are very similar to those of the Brown Recluse spider and often people bitten by Hobo spiders think they were bitten by a Brown Recluse spider, although those two species do not coexist in the same geographic regions.
Life-cycle
The life-cycle of males is particularly interesting. The male will retreat to the females burrow to mate for an extended period of time (1-2 weeks). The female does not eat him after mating, but he dies automatically due to the seriousness of his efforts. When the male Hobo is dead, the female eat him.
Lesser house spider or common house spider
Both named are used to describe Tegenaria Agrestis, a close sibling to the Hobo spider. In contrast to its venomous cousin, the house spider is not venomous. It is found throughout most of the US and Europe. It is very difficult to discriminate between this spider and the hobo spider as their size is approximately the same and they have the same chevron pattern on their abdomens.
Giant House spider
Until the mid-nineties this spider was known as Tegenaria Gigantea although it has later been shown that it is in fact identical to Tegenaria Duellica. It can move extremely fast and it is probably the quickest spider in the world, as it can reach a speed of 0.53 m/s or 1.73 feet/s. It is almost as fast as the Camel spider. The Giant House spider is venomous although it is not known to envenomate humans. The Giant spider is truly gigantic, as it can reach a length of 10 cm.
Tegenaria Atrica
This spider was until recently only found in Europe and Northern Africa. Now it also spreads fear in the United States.
Tegenaria Duellicas
This giant spider is found in Europe and in the United Kingdom. It is a Tegenaria though. European hobo spiders are all considered benign4.
The fact that European variants of Tegenaria are considered rather benign makes it difficult to believe that their American counterparts are as dangerous as people believe.
References
1. Exline, H. Tegenaria agrestis (Walck.), An European spider introduced into Washington State. Ann. ent. Soc. Amer (44) pp. 308-310 (1951)
2. Baird, C.R. & Stoltz, RL. Range expansion of the hobo spider, Tegenaria agrestis, in the northwestern United States (Araneae, Agelenidae). J. Arachnol (30) pp. 201-204 (2002)
3. Vest, D.K. Envenomation by Tegenaria agrestis (Walckenaer) spiders in rabbits. Toxicon 25(2) pp. 221-224 (1987)
4. Goldfrank, L.R & Flomenbaum, N. Goldfrank's toxicologic emergencies. (2006)