Utah Plant Pest Diagnostic Lab
Hobo Spiders (Eratigena agrestis)
About this Page
Since the late 70's the Utah Plant Pest Diagnostic Lab has kept track of all submitted samples. To date, we have had over 13,500 samples submitted, 10,077 of which are insects, spiders, mites, etc. There have been about 2,188 spiders submitted since 1978. Of those samples, 1,211 have been funnel web spiders (Agelenidae), and 639 have been hobos! The first hobo sample was submitted in 1990. If you have questions regarding the other arachnids frequently encountered in Utah, please visit our Top 20 Arachnids page.
By far, hobos are the number 1 spider submitted to the lab, and this is because of their frequency in peoples' homes, their size and speed, and the fact that people fear hobos. Because of the volume of samples, phone calls, and emails we receive about this spider, This page was developed to answer any questions you might have about hobo spiders and their control. Some of the information on this page is technical and may seem too complex or difficult; however, knowledge of this information is what is necessary to properly identify a hobo spider. Without a microscope and some level of expertise you cannot distinguish a hobo spider from other similar-looking spiders. If you catch a spider and would like to have it identified visit this page for instructions on submitting a sample.
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.
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.
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.
Description and Identification
The hobo spider is a member of the funnel-web spider family Agelenidae (not to be confused with funnel web tarantulas in the family Hexathelidae commonly found in Australia). Funnel-web spiders are long-legged, swift-running spiders that build funnel or tube-shaped retreats. The hobo spider runs at an average speed of about 0.45 meters (17 inches) per second, with a maximum speed of about 1.1 meters (40 inches) per second.
While the hobo spider greatly resembles certain other members of the funnel-web spider family, which are harmless, it has important distinguishing characteristics.The hobo spider has a brown cephalothorax (the front body region where the legs are attached) with darker brown markings and brown legs. The abdomen (the second body region) has a distinctive pattern of yellow markings on a grey background, although this pattern can be difficult to discern without the aid of a microscope or hand lens. The pattern is generally more distinctive in immature specimens. Unlike many other similar-looking spiders, hobo spiders do not have dark bands (e.g., multiple arm bands) on their legs. Spiders with such banding are not hobo spiders.
Mature female hobo spiders are 9.5-16.5 mm (3/8-5/8 in) long, and male hobo spiders are 7-13.5 mm (9/32-9/16 in) in body length. Males have enlarged pedipalps located near the mouth, resembling short legs.
Identifying a hobo spider requires the use of a microscope. The presence of a brown spider in your home does not mean that it is a hobo--there are many brown spiders that look similar to hobos. Additionally, you cannot identify a hobo based on the "chevron" markings on the abdomen; many spiders have a very similar appearance to a hobo. See this page for more info. To properly identify a hobo spider, three key characteristics should be observed under a microscope. The following characteristics should be used when identifying a hobo spider: 1. plumose setae, 2. 8 eyes in two nearly straight rows, and 3. cheliceral retromargin with 6 to 8 teeth (vs. domestic house spiders and grass spiders which have 3 to 5 teeth on the cheliceral retromargin).
Identifying a Hobo Spider with a Microscope
Plumose setae are diagnostic of the family Agelenidae, or the funnel web spiders. These fine, almost clear hairs have a feather-like appearance. A microscope or strong hand lens is needed to see these hairs. Do not be confused by the large black spines, or smaller, thick black hairs. The plumose hairs lay nearly flat against the body and are difficult to see.
Plumose setae do not differentiate between species of Agelenidae, but if your spider lacks these setae, then you can rule out having a hobo spider.
This picture shows the 6 to 8 teeth which can be found on the cheliceral retromargin. This structure can be looked at by removing the chelicera from the spider and turning them over. The retromargin is the one that would have been closest to the mouth when the chelicerae were still attached to the spider.
In addition to the above characters, a hobo can be separated from other spiders by the combination of the following characteristics:
The sternum of a hobo spider will have darker outer edges and a lighter inside.
The male "boxing gloves" or palps are part of the spiders reproductive system. Genitalia can be used by arachnologists to identify spiders to species. The hobo palp has two prongs as indicated by the red arrows. Closely related species such as the domestic house spider and the giant house spider will only have one prong.
Additional identification guides can be found at the following links:
Utah State Univ.
Washington State Univ.
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.
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:
- To find a mate during mating season (August-October for hobos).
- To find prey (i.e. other insects in your home).
- The home is not adequately “spider proofed.”
Spider inand around your home can be minimized by using the following techniques.
- 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.
- 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.
- 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.
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:
- 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.
- The bite victim must submit the specimen for an official identification by a qualified arachnologist.
- The spider must be identified to species as Eratigena agrestis.
- 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.
|Evidence For||Evidence Against|
|In 1987, Darwin Vest studied forced envenomation by male hobos on rabbits. 4 New Zealand white rabbits bitten by male spiders developed necrotic lesions.||In the same 1987 study, Darwin Vest studied forced envenomation by female hobos on rabbits. 5 rabbits (4 New Zealand White & 1 CA giant rabbit) did not develop necrotic lesions. Sample size for both the male and female portions of the study are too small to draw definitive conclusions from.|
|In Europe, hobos do not typically live in domestic dwellings and therefore do not come into contact with people (Jones 1983; Roberts 1985). The argument is that if hobos don't commonly come into contact with people in Europe, then the fact that they are not medically significant in Europe is due to that fact rather than the toxicity of their venom.||Binford and Gomez attempt to replicate Vest's 1987 study, but without success. They could not get hobos to bite rabbits, suggesting they are not aggressive biters. Male and female venom extracted from hobo spiders was injected into rabbits and no necrotic lesions formed. This study had small sample size and was not published (Binford and Roe personal communication 2006).|
|In the US, hobos frequently come indoors where people are, and could potentially bite (Akre and Catts 1990).||Results from studies conducted on rabbits cannot be directly extrapolated to humans.|
|Many purported, but not verified bites from many people who claim a hobo bit them. This is not science based||People living in states where hobo spiders have not been documented have been misdiagnosed by physicians as having bites from hobo spiders (Vetter et. al 2003).|
|Case studies of non-verified hobo bite victims linked to the development of necrotic lesions in the PNW (Vest 1987)||Hobos occurring in Europe, which is where our hobos came from, are known to bite humans but without adverse effects (Preston-Mafham 1984).|
|Case studies of non-verified hobo bite victims linked to the development of necrotic lesions in the PNW (Akre and Myhre 1991).||An analysis of hobo venom between UK (United Kingdom) and US spiders was not significantly different; results are in conflict with the idea that US hobo venom is different than UK hobo venom (Binford 2001).|
|One case study where hobo spiders were found in a home of someone who developed a necrotic lesion (Fisher et al. 1994)||Reports of "spider bites" are greatly influenced by the fact that most people fear spiders, and because of this fear most unknown bites are blamed on spiders (Anderson 1982).|
|One case study of a women developing a nodule with pustules, inflammation, and 2 areas of ecchymosis after feeling a "bite" in bed. A hobo was found on the wall the next day and determined to be the cause (Sadler et al. 2001).||Russell and Gertsch (1983) examined 600 suspected spider bite with the finding that 80% were caused by arthropods other than spiders or by other diseased states.|
|One 42-year old woman with a history of phlebitis (a disease that can cause ulcers) crushed a hobo spider in her pants after feeling a burning sensation developed a necrotic ulcer.||There are many medical conditions which can manifest as necrotic lesions or skin ulcers, including bacterial, viral and fungal infections, drug reactions, diseases such as diabetes, other arthropod bites, and more (Vetter 2004). See the table below.|
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.
Underlying Disease States
Reaction to Drugs
Miscellaneous/Multiple Causative Agents
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.
Here are a few of my favorite fact sheets on spiders in the home:
- Spider Myths Website...a MUST read!
- To view our lab's top 20 most frequently identified arachnids click this link.
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.