History and Distribution

The hobo spider, Eratigena agrestis, is native to Europe and was introduced into the Pacific Northwest in the 1930's. The spider has expanded its range south and east, and can be found extensively throughout northern Utah (Vetter et al. 2003). Originally, the hobo spider was named "the aggressive house spider," which originated from an incorrect interpretation of its species name-agrestis-which means "of the field or land." This name was given in reference to the hobo's habit of living in grassy fields in its native Europe where it is displaced in homes by its relative, the giant house spider. Giant house spider has also been introduced into the Pacific Northwest, however there are no records of this spider in Utah.

Life Cycle

There is some disagreement among researchers as to the length of the hobo spider life cycle. Only one year may be required to complete a generation among the warmer coastal regions; however, inland populations, such as those living in Utah, are believed to require two or three years to complete a generation.

Eggs deposited in the fall begin hatching in the spring. The spiderlings will molt (shed their skin) once before breaking free from the egg sac around early June. The juvenile hobo spiders grow and develop over the summer (or several summers) and will overwinter again before reaching maturity the following year. Males and females will mature from June to September. Males seek out females for mating during the summer and most die before October. Mated females start laying eggs in mid-September, with one to four egg sacs produced over a period of four weeks. Fewer eggs are produced if food is limited or if temperatures are cooler than normal. Cold temperatures eventually terminate the production of eggs by the females. Most females will die in late autumn, but some may overwinter and live into the following summer.

Habits

Hobo spiders frequent areas such as log or timber piles, rock piles/borders/retaining walls, holes, or where tall grass meets the foundation or crevices in soil or concrete where they can make their characteristic funnel webs. The webs are funnel shaped, sort of like a tornado but really wide at the top. The spider waits in the small hole at the bottom of the funnel for prey to make contact with the web. When it senses a vibration it will emerge from the hole to envenomate its prey. Funnel web spiders have "feet" designed for walking on their webs and large hobo spiders aren't designed to climb smooth surfaces in homes, such as painted walls. Consequently, when they enter homes they are usually found at ground level in the basement because they cannot climb walls or slick surfaces to escape. A common place to find hobos is in the bath tub or sink because the porcelain or plastic is too slick for them to climb. However, this is not to say hobos can't climb. They can easily climb carpeted stairs, curtains, towels, bed skirts, highly textured walls, cement walls, brick, etc. Funnel web spiders, the hobo and domestic house spider in particular, can be found frequently in homes while wandering in search of mates in August through October, and when looking for web sites in the spring.

Why are hobos in my house?

In Utah, hobos are frequently found indoors from August through October. This inward migration is driven by their mating season. Males are searching for females at this time and are following chemical scents (pheromones) given off by female hobo spiders. Houses with old or broken door sweeps, windows/screens, no weather stripping around exterior doors, foundation cracks, etc., are at greater risk for hobo invasion. Fix these structural issues and the number of hobos capable of coming into the home will decrease. You can use non-pheromone baited sticky traps to monitor areas where you suspect hobos might be entering. After mating, the males will die. Females will move outside to deposit their egg sacs and will also die. Juveniles may be found in the home throughout the remainder of the year, but are infrequent.

Control Methods

Almost every home in northern UT likely has at least one hobo spider at some point during the year. They are difficult to spot, however, because they are active at night. Because hobos aren’t great climbers people often find them in the basement or in a porcelain tub/sink in the morning.

The following section covers control methods for hobo spiders and spiders in general. Spiders should be considered beneficial, but sometimes their presence is unwanted. Spraying insecticides is generally not recommended for control of spiders unless there is a large infestation. Spraying, in the long run, could make hobo spider problems worse by reducing spider diversity around homes, minimizing competition for spiders. Spiders can be readily killed by a direct spray of insecticides however, an insecticidal "barrier" around the home is unlikely to provide perfect control of hobos as insecticides used for killing insects are generally not as effective against spiders. Additionally, many hobo spiders are coming in from the property and run quickly into the home and may not be in contact with the chemical long enough to cause mortality. I have observed hobo spiders running right up the concrete steps into my home on many occasions. If the door sweeps aren't in tact and the entry ways sealed, you will still have an occasional hobo entering the home.

To control spiders it is necessary to understand why and how they enter the home and use that knowledge against them. Below are the major reasons spiders enter the home:

1. To find a mate during mating season (August-October for hobos).
2. To find prey (i.e. other insects in your home).
3. The home is not adequately “spider proofed.”

Spider inand around your home can be minimized by using the following techniques.

Exclusion

• Replace doorsweeps on all outside doors (probably the most important thing you can do). The sweep must come in complete contact with the ground surface and both sides of the doorway. Even a few mm of space is enough for spiders and other pests to enter the home.
• Seal all foundation cracks and crevices leading into the home with silicon caulking or sealant.
• Install weather stripping around doors and windows, especially all doors leading to the outside. This includes the garage door.

Cleaning and Habitat Modification

• Vacuum regularly. Spiders often come inside to find mates, but they stay inside because they can find food (other insects). By vacuuming regularly and implementing the exclusion techniques mentioned in points 1-3, you can minimize insects (spider food) in the house and keep spider populations down naturally. Spiders, webs, and egg sacs can also be sucked up (hobo egg sacs are found outside).
• Minimize clutter. Spiders love secluded places to hide and lay egg sacs. If you have a lot of boxes or stuff lying around the home, especially in the basement, garage, or other storage areas, those are perfect places for spiders to hide and lay eggs. Outside the home, woodpiles, rock borders, lawn ornaments, etc. can all provide suitable places for hobos to hide and to lay egg sacs. Simplify the environment by putting items in sealable storage bins, moving rock and log piles away from the home, etc.
• Change exterior lighting. Insects are attracted to "normal" exterior lights at night. The increase in insects (spider food) will also attract an increased number of spiders looking for food. To minimize the number of insects attracted to the house, replace the regular light bulbs with sodium vapor lights which are less attractive to insects.

Monitoring

• Sticky traps. The standard sticky traps you purchase at the lawn and garden shop placed around the baseboards of the home will tell you what type of spiders are present (if they are ground dwelling spiders), and can capture hobos. Traps can be discarded and new ones set out as they become full.
• Traps can also tell you where spider or insect "hot-spots" may be in the home, or give you information as to where the spiders may be entering the home. Control efforts can then be concentrated in those areas. Traps with pheromones can trap more hobo spiders, but the traps can act as an attractant, drawing in more spiders from outside than would normally come in.
• Avoid using hobo pheromone baited traps from August to October in Utah. Sticky traps should be folded and placed firmly against the baseboards where children and pets cannot access them.
• During "hobo season" consider placing one or two traps in every room, and on either side of the bed against the baseboards to increase trapping/control.

Chemical

• In secluded areas, crawl spaces, cracks and crevices, or wall voids (areas where people won't be coming in contact with chemicals), you can use a dust formulation of an insecticide composed of a pyrethroid, or one composed of silicate or diatomaceous earth purchased at the local home and garden store. Do not use this product as a broadcast treatment over floors, etc., where people may contact it.
• Liquid or dust insecticides may be applied directly to webs (this works especially well for black widow spiders).
• Non-residual aerosol sprays can be used to directly spray spiders; spiders not directly contacted with this treatment will not die.
• If an outside perimeter treatment is desired, insecticide sprays are best timed for when hobo egg sacs are hatching. This will depend largely on temperature, but you can expect eggs to hatch from mid May to Mid June in UT. Suspension concentrates, capsule suspensions and microencapsulated formulations work best for spiders. The reality, though, is that most people will want the application during "hobo season" which may provide some relief from hobo spiders, though thorough exclusion measures taken above may provide the same level of control indoors, if not better.

Bite Prevention Tips

• In August through October, there is usually an influx of hobos and other spiders entering the home as the mating season picks up. This time of year it is advised to remove the bedskirt from the bed and pull the bed about 8 inches out from the walls. This will help keep wandering hobos out of your bed and minimize the chance of rolling over on one during the night.
• Take caution when picking clothes up off the floor or in laundry baskets. Spiders hiding in these clothes can be mistakenly grabbed resulting in a bite.
• Keep childrens' toys off of the floor where spiders can hide under them.

Combining all or some of the techniques listed above to minimize the number of hobos coming into your home.

Hobo Bites

People fear hobo spiders because information about their potentially necrotic (flesh eating) bite has been perpetuated in the medical literature and among people. More recent evidence would suggest, however, the likelihood of hobo spiders having venom of medical importance to humans is extremely unlikely. There is no good scientific evidence to suggest that this is the case. Unfortunately, there is a lack of verified hobo spider bites.

In order to verify that hobos have a necrotic bite, we would need to follow many confirmed cases over a multiple year period and relate bites to the development of necrotic lesions. The key word is "confirmed" bite. Anecdotes and stories don't count as scientific evidence. In order to have a confirmed bite, the following must happen:

1. The person must actually see or feel the spider biting them, and then capture the spider immediately before it gets out of sight. If you have a lesion on your body and you see a small brown spider in your home a few days later, hobo or not, you cannot blame that spider. A spider's presence in the home does not automatically implicate the spider.
2. The bite victim must submit the specimen for an official identification by a qualified arachnologist.
3. The spider must be identified to species as Eratigena agrestis.
4. Finally, the bite area must be followed by the doctor to determine if a necrotic lesion develops.

Considering that almost everyone in Northern Utah has hobos in their home from August to October, seeing one in the bedroom does not implicate the spider. Below is a table comparing the evidence for and against hobos having a necrotic bite. Unfortunately, there is no conclusive evidence to suggest that either side is correct without a doubt; however, you will notice that the "evidence for" is highly circumstantial, while "evidence against" is scientific. For a more detailed discussion on this topic see this publication by Vetter.

The table below was adapted from the University of California Riverside's "Causes of Necrotic Wounds other than the brown recluse spider" website (Vetter 2004). This information is presented to let people know that there are other causes of necrotic wounds than from spider bites, and they can be serious or life threatening conditions.

Spiders of concern in Utah

The major spider of concern in Utah is the adult female black widow spider. The adult female black widow spider is solid black in color and has a red hourglass shape on the underside of the abdomen. Immature male and female resemble each other and are brown with banding on the legs and white stripes on the top of the abdomen. For more information on black widow spiders visit this page.

Links

Here are a few of my favorite fact sheets on spiders in the home:

• http://www.ext.colostate.edu/pubs/insect/05512.html
• http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7442.html
• Spider Myths Website...a MUST read!
• To view our lab's top 20 most frequently identified arachnids click this link.

References

Akre R.D. and Catts E.P. 1990. Spiders. Washington State University Cooperative Extension, EB 1548, 8p.

Akre R.D. and Myhre E.A. 1991. Biology and Medical Importance of the Aggressive House Spider, Tegenaria agrestis, in the Pacific Northwest (Arachinida: Araneae: Agelenidae). Melandria, Vol. 47:1-30.

Anderson PC. 1982. Necrotizing spider bites. American Family Physician, 26:198-203.

Binford G.J. 2001. An analysis of geographic and intersexual chemical variation in venoms of the spider Tegenaria agrestis (Agelenidae). Toxicon, 39:955-968.

Binford G.J. and Roe A. 2006. Personal communication via email.

Fisher R.G., Kelly P., Krober M.S., et al. 1994. Necrotic arachnidism. Western Journal of Medicine, 160:570-572.

Jones D. 1983. The Country Life Guide to Spiders of Britain and Northern Europe. London: Country Life Books.

Preston-Mafham R. and Preston-Mafham K. 1984. Spiders of the World. Facts on File: NY, 191p.

Roberts M.J. 1985. The Spiders of Great Britain and Ireland. Atypidae to Theridiosomatidae. Harely:Essex, England, 1:229p.

Russell F.E. and Gertsch W.J. 1983. For those who treat spider or suspected spider bites (letter). Toxicon, 21:337-339.

Sadler MA, Force RW, Solbrig RM, et al. 2001. Suspected Tegenaria agrestis envenomation. Annals of Pharmacotherapy, 35:1490-1491.

Vest D.K. 1987. Envenomation by Tegenaria agrestis (Walckenaer) spiders in rabbits. Toxicon, 25:221-224.

Vest D.K. 1987. Necrotic arachnidism in the northwest United States and its probable relationship to Tegenaria agrestis (Walckenaer) spiders. Toxicon, 25:175-184.

Vetter R.S., Roe A.H., Bennett R.G., et al. 2003. Distribution of the medically-implicated hobo spider (Araneae: Agelenidae) and a benign congener, Tegenaria duellica, in the United States and Canada. Journal of Medical Entomology, 40:159-164.

Vetter R.S. 2004. Causes of Necrotic Wounds other than Brown Recluse Spider Bites. University of California Riverside. http://spiders.ucr.edu/necrotic.html. Last accessed August 19, 2011.

Vetter R.S. and Isbister G.K. 2004. Do Hobo Spider Bites Cause Dermonecrotic Injuries? Annals of Emergency Medicine. December, 44:6.