Hobo Spider, a.k.a. Aggressive House Spider
Identification: Firstly, we need to clear the air of spiders in Whatcom county. We do have Black Widow spiders but they are extremely rare. We do not have the Brown Recluse spiders in the Northwest. In our area, we have a complex of three species of house spiders. Unfortunately, all three species look very similar. This is why it is important to regard all house spiders as potential hazards and to be cautious when handling, smashing, stomping, vacuum sucking or what ever you do. The three species include the domestic house spider, Tegenaria domestica, the giant house spider, T. gigantea, and the Hobo spider, T. agrestis. The domestic spider is the most commonly encountered spider in your house and is the smallest spider of the three (less than a ½” in body length). The giant house spider will usually be obvious, these spiders are huge! My first impression up here, in what I initially thought was a paradise free of anything nasty, was shattered when a large giant male scattered across my wall in that disturbing spider fashion. Generally, the hobo spider is medium to medium large. The body alone can be up to ¾” in length in mature adults. What will stand out the most, is the multiple chevron pattern on the abdomen. Legs of the hobo spider have no stripes (different from domestic and giant spiders). The sternal pattern (markings on the underside of the cephlothorax) of hobo’s have a light tan center with dark bands on the sides where the legs join (while domestic and giant spiders have small circles on the sides). Again, when identifying these spiders, there are always exceptions to the rule.
Life History: Domestic spiders will be around all year while most encounters with hobo spiders will occur in the late summer and fall (hobo mating season). Males are on the search for females, so they will be running everywhere in hopes of an encounter. When males enter a house, it is usually through ground level or below ground level openings. Hobo spiders rarely climb very high. For the rest of the year, spiders will build webs in moist, cool, outdoor environments. Hobo spiders really do prefer to be outside in meadows and woodpiles. Occasionally, webs and egg cases will be constructed inside basements or crawlspaces. These webs are recognized by the characteristic funnel shape. Egg cases will be made during the fall through November.
Damage: All spiders are venomous and use their venom as a means of prey capture and not defense, unlike bees and wasps. As of yet, hobo spider bites are not fatal. Most bites and disturbances occur starting in August and go until the first big freeze. In fact the male hobo, which is more likely encountered, is more toxic than the female. The severity of a bite is about as variable as people are. It is believed that up to half of the bites by hobo spiders are ‘dry bites’ meaning that no venom was secreted. Bites can affect someone directly (meaning that the bite area shows evidence of a bite) or systematically (like an allergic reaction). Hobo spider bites can directly cause skin necrosis. At first, the bite may appear as a mosquito bite which will then blister. After blistering, the lesion will ulcerate and possibly turn black as the tissue dies. This is common in areas where the skin is soft. Pending on the severity of the bite and the individual’s reaction to it, the wound may heal in a month or two years. Systematic reactions include most allergy symptoms such as nausea, fever, headaches and joint soreness. It is very important, if you are bitten by a spider, that you collect the spider and get it identified correctly. Identification will help physicians react to the injury appropriately. For example, do not take aspirin for a hobo bite. The venom is injected with a spreading agent that will travel further in thin blood.
Control & Prevention: For in-house encounters, simply barricade the area that the spiders are using to get in. At my house, it is the gap underneath my front door. I simply put window adhesive to close the gap. Additionally, sticky traps are quite effective in areas that you have many spiders making their way in. During peak season last year, I watched 18 spiders come in through my doorway in one night! The sticky trap caught all 18 of them. For large infestations underneath the house or in basements, chemical control may be a consideration. When moving any debris or wood out side, wear protective clothing and gloves. This is also very important when venturing into areas of known infestations such as the crawlspace. Be sure to check your gloves and shoes before you put them on. This is the most common scenario for a bite. Finally, the best and most long-term solution (but probably the most undesirable) is to let nature take its course. In Europe, where all three species of house spiders come from, the hobo is not a problem inside the house. The hobo spider was introduced prior to the giant house spider. Now the giant spider population is increasing, while the hobo spider is decreasing in frequency of occurrence. As a result, the number of bites in the household is decreasing. The giant spider is a fierce competitor of the hobo spider and will keep hobo’s out of its territory. In addition, the giant spider is relatively harmless and bites are rare. This is why hobo’s are not a problem in Europe, they are naturally controlled. Soon, we will expect to see the same results here. Kudos to you if you’re able to tolerate giant house spiders in your home; aside from their shocking nature, they are the good guys in this case. Have you hugged your Giant House Spider today?
For all the information you ever wanted to know about house spiders, see: http://hobospider.org.
This article was written in 1997, check out the Hobo Spider Up-date: http://whatcom.wsu.edu/ag/homehort/pest/hobo2.htm
For an excellent page to identify Hobo Spiders: http://pep.wsu.edu/pdf/PLS116_1.pdf
For additional Whatcom County spider information: http://whatcom.wsu.edu/ag/homehort/pest/spider.htm
To reach Todd Murray please call (360) 676-6736 or e-mail him at: firstname.lastname@example.org