Hobo Spider Bite
Last reviewed by Dr. Raj MD on January 12th, 2022.
What is a Hobo spider?
The hobo spider has other common names such as funnel weaver and aggressive house spider.
Its actual scientific name is Eratigena agrestis pronounced as air-uh-TIH-jen-uh ah-GREZ-tiss. Eratigena comes from the name Tegenaria and agrestis means from the fields or growing wild. It was previously called Tegenaria agrestis in the scientific field. (6)
Where do Hobo spiders live?
Hobo spiders are found in the states of Washington, Oregon, and Idaho in the United States. This spider came to the US from Europe. The cases of many “brown recluse” spider bites in these areas are now being understood to be bites from Tegenaria agrestis or the hobo spider.
The hobo is considered in the list of domestic spiders meaning it is found indoors, or in one’s home. (1, 2)
Image 1 : In this image, the green area is where infestations of Hobo spiders in the united states has been found.
Photo Source : upload.wikimedia.org
Hobo spider bite Pictures
What does a hobo spider bite look like
Figure 2 : This image shows the blister stage of a Hobo spider bite.
Picture Source : mddk.com
Picture 3 : In this stage, the blister has not opened up and the ulcer has not begun.
Image Source : allpests.org
Figure 4 : This image shows the stage after the blister opens and the ulcer begins to grow.
Photo Source : i.ytimg.com
Image 5 : In this image, the ulcer is creating scar tissue and is beginning the healing process.
Picture Source : mddk.com
Hobo spider bite case studies.
The following are case studies noted by the CDC in cases where the T. agrestis or hobo spider was known to be near:
- 10yr old boy in Oregon– lesions were found that were hot to the touch within two days of the bite. A week after the bite the skin began to fall off and die. The patient stated systemic symptoms such as nausea and headache. The headaches lasted almost 4 months and the wound took over 30 days to heal completely.
- A 42-year-old lady who reported dizziness, headache and being nauseated within 3 hours of a bite. The bite became severely swollen and within 24 hours opened and let an ulcer like a wound. The bite even after healed left a crater like a scar and the patient is unable to bear weight for long amounts of time.
- A 56-year-old patient who also mentioned a severe headache, nausea, and confusion. The patient was admitted for aplastic anemia and eventually bleed out and died. This patient did not seek treatment when the bite was first noticed.
Side effects of a Hobo spider bite
Hobo spider bites can cause toxicosis and have often been seen with necrotic arachnidism. Necrotic arachnidism is basically a spider bite which has caused tissue death. The bites that have been determined to be from Hobo spider bites shows that tissue death can occur. With this tissue death, nerve damage or difficulty using the affected limb could result. See case studies in above section. (1, 2, 3)
Hobo spider bite timeline (Stages)
| Initially painless |
| Small indentation in 30min |
| Blister development 15-35 hours |
| Blisters rupture forming crater |
| Necrosis and sloughing up to 40days |
| Healing and permanent scaring within 45 days |
Hobo spider bite Treatment
There is no one cure for a spider bite. Usually, treatment consists of treating systemic effects from the bite as well as trying to control the wound.
Sometimes corticosteroids are given to help with decreasing swelling. Antihistamines may be prescribed as well. Eventually, surgical repair of the area may be needed depending on the amount of tissue damage. (2, 8, 9)
Hobo spider identification
Most of the times identifying a spider must be done in a lab. Many different species of spiders and especially domestic spiders can appear very similar. Especially because most of the times they have been killed or smashed upon collection.
In this case, a test of the specimens DNA is what can determine its identification. Also, a microscopic inspection of the sex organs can help to ID the arachnid. (1, 2, 8, 9)
Picture 6 : This is an image of how the female sex organs can be identified under a microscope.
Photo Source : bugguide.net
Figure 7 : This image shows the male sex organs of the male Hobo spider.
Image Source : bugguide.net
With this in mind, there are physical markers which could help one to identify the Hobo spider without lab equipment.
- They do not have colored bands at the leg joints like many other spiders.
- They have a V shape on their abdomen with the tip of the V pointing towards the head.
- Most have only one light stripe down its back.
- They have eight eyes like other arachnids
- Their legs are long and thick, they are the same color as their body.
- Their web is funnel shaped and looks like a flat sheet. (3, 6, 8, 11)
Image 8 : This is a very clear picture of what a hobo spider may look like it.
Photo Source : upload.wikimedia.org
Picture 9 : This is a confirmed male Hobo spider, in this image you can see the dark brown color and verify that there are no ring marks near the legs.
Photo Source : upload.wikimedia.org
Figure 10 : This image was chosen to show the difference between the male and female hobo spider.
Picture Source : www.spiders.us
Picture 11 : This image is chosen to show the close up of the back of the spider and the leg connections. The color looks very light due to the lighting.
Image Source : www.spiders.us
Photo 12 : This picture shows yet another view of the male Hobo spider one which was captured in Washington.
Picture Souce : www.spiders.us
Figure 13 : Here the spider is standing on the tip of a file which can help to understand its size.
Image Source : www.spiders.usPicture 14 : This image depicts the female Hobo spider with her egg sack.
Photo Source : www.spiders.us
Image 15 : Here is a clear image of the frontal view of a female Hobo Spider.
Picture Source : www.spiders.us
Figure 16 : In this image, you can see what the egg sack will look like when the female Hobo spider is finished constructing it.
Photo Source : www.spiders.us
Image 16 : This shows a number of egg sacs that just one female Hobo Spider is capable of creating.
Picture Source : www.spiders.us
Are Hobo spiders aggressive?
The name agrestis does not mean aggressive although this has been a common misconception. The scientific name for the Hobo spider, agrestis, really means of the fields. In Europe, due to a larger house spider, these spiders are usually found in the fields. In the United States, they are found indoor and the scientific name was misused and the Hobo spider has been called the “aggressive house spider.” (3)
Resources:
- https://www.ncbi.nlm.nih.gov/pubmed/3576634
- https://www.cdc.gov/mmwr/preview/mmwrhtml/00042059.htm
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3088024/
- https://en.wikipedia.org/wiki/Hobo_spider
- https://es.wikipedia.org/wiki/Eratigena_agrestis
- http://www.spiders.us/species/eratigena-agrestis/
- http://bugguide.net/node/view/31446
- http://animaldiversity.org/accounts/Tegenaria_agrestis/
- http://guadarramistas.com/2014/06/09/tegenaria-arana-domestica/
- http://www.uniprot.org/taxonomy/1686644
- http://utahpests.usu.edu/uppdl/htm/hobo-spiders
Necrosis and sloughing up to 40days