Medical News Today: Hobo spider bite: What you need to know

The hobo spider is a type of funnel-building spider native to Europe. It is not usually aggressive unless provoked and there have been very few confirmed cases of hobo spider bites.

The species was introduced to North America in the 1900s and today inhabits several American states and Canadian provinces in the Pacific Northwest.

While the hobo spider was thought to be toxic in the past, today its venom is widely considered non-toxic and their bites non-necrotizing (non-tissue destroying).

Hobo spider bites are rare and tend to be mistaken for bites from other toxic species, such as brown recluse spiders.

What is a hobo spider?

Hobo spider on a wall
Hobo spiders are not known to bite unless provoked.

Hobo spiders get their common name from the belief that the species has spread throughout the United States via railways, and because of their tendency to live in places with hidden cracks, such as rock walls and brush piles.

During the mating season, which stretches from the late spring to the fall, hobo spiders can also live indoors.

The species are not known to bite except in self-defense or when catching prey.

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Very few studies have examined confirmed hobo spider bites. Hobo spiders are also commonly visually mistaken for their more dangerous relatives, brown recluse spiders.

Because there are so few confirmed cases of hobo spider bites in North America, the associated symptoms and complications remain unclear.

Over time, some studies have reported a wide range of side effects that may be linked to hobo spider bites. But most research suggests that many people only feel a prick or sting when bitten and minor skin irritation afterward.

Unconfirmed symptoms and complications associated with hobo spider bites include:

  • a headache that lasts up to 7 days
  • exhaustion
  • bone or joint pain and weakness
  • muscle weakness
  • dry mouth
  • nausea and vomiting
  • blurry or double vision
  • hallucinations
  • fever
  • confusion
  • severe and sudden swelling
  • hemorrhaging or internal bleeding
  • organ failure
  • coma
  • death

Physical signs of the spider bite include:

  • prolonged inflammation, or pain, redness, and swelling
  • tingling or numbness
  • muscle twitches
  • skin infection, especially in people with immune conditions
  • ulceration, or open skin wounds
  • scarring in rare instances

Stages and complications

Hobo spider bite
Within 24 hours of a hobo spider bite, a fluid filled blister may appear over the wound.

In rare cases, hobo spider bites have been reported to cause symptoms similar to that of a bite from a brown recluse spider.

Stages of these rare reactions from hobo spider bites are:

First few minutes

The bite is typically painless and unnoticeable initially, although it may cause a pricking, stinging, or burning sensation.

After a few minutes, the bite may become inflamed, red, painful, and swollen. Some accounts describe the bite as looking like a mosquito bite.

First few hours

Inflammation may spread several inches from the site of the bite. The bite itself may begin to look more like a bee, wasp, or hornet sting.

Within 24 hours

A clear, fluid-filled blister may form directly over the wound site.

Within 24 to 48 hours

The blister will usually rupture on its own, releasing clear or very pale yellow-colored fluid. Once the blister has drained, it will leave behind an open wound or ulceration. The wound will be tender, sore, and painful, especially when exposed to the air or irritated.

1 to 3 weeks

The time it takes for the wound to heal will depend on how severe it is and how well a person cares for it.

As the wound heals, it will form a protective scab. The scab helps seal the wound while it heals, keeping out dirt, bacteria, viruses, and fungi. Once the wound is healed completely, the scab will fall off.

Rarely, a large blister may cause scarring. Scarring and necrosis are also more likely to occur in people with a compromised immune system or who have chronic medical conditions.

While unproven, it is possible that a small portion of the population is allergic to hobo spider bites or venom.

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Hobo spider on white background
Keeping the area clean and dry will be recommended for hobo spider bites.

In most cases, there is no strict treatment method for a hobo spider bite other than to keep the site clean and dry. Most skin complications, such as rashes, are caused by bacterial infections not a reaction to the bite itself.

Hobo spiders do not usually inject venom when they bite, so often the best thing to do after being bitten is to wash the site with soap and water.

After the area has been cleaned and dried, cover the bite with a sterile bandage or gauze to keep out dirt and bacteria.

It is essential to clean the bite and replace the coverings every day while the wound heals. If a blister forms, a person should take care not to pick at it.

Bites that cause sudden or severe symptoms may be a sign of an allergic reaction to the spider’s salivary proteins or venom and require immediate medical attention.

While awaiting medical care, wash the bite with clean water and soap. Icing and elevating the area can also help reduce symptoms in the short-term.

There is no set procedure for treating hobo spider bites, so most doctors treat them similarly to brown recluse spider bites.

Treatment options for these bites may include:

  • precautionary vaccines, such as a tetanus vaccination
  • antihistamine medications to reduce inflammation
  • corticosteroid creams and lotions to limit inflammation
  • antibacterial medications to prevent infection
  • intravenous fluid therapy (IV)

Treatments that are commonly used for brown recluse spider bites but not often for a non-toxic bite include colchicine-based medications and oxygen therapy.

When to see a doctor

Because the actual side effects and complications of hobo spider bites remain unknown, it is crucial for people who think they have been bitten to seek medical care and monitoring.

Bites or wounds that have become discolored or infected during the healing process also require medical attention and treatment.

Seeking medical attention for suspected spider bites can also help researchers better understand the human risks associated with hobo spiders.

Symptoms of spider bites that require medical attention include:

  • severe swelling and pain
  • blistering
  • loss of sensation
  • sudden darkening of the skin
  • a headache, nausea, or vomiting
  • blurred vision
  • confusion
  • muscle pain or weakness
  • joint or bone aches
  • fever
  • skin rash surrounding the bite or somewhere else on the body

After a physical examination of the bite, a doctor may take pictures of the bite area. They will also ask a person about any other symptoms they are experiencing.

If possible, a person should carefully collect any spiders or other insects that may have caused the bite and bring them to the emergency room in a sealed container.

Some doctors and medical facilities have access to an anti-venom, or medication that can reverse the effects of the spider’s toxin within the first 4 to 12 hours.

Hobo spiders can usually only be accurately identified using a microscope. For proper identification, the spider needs to be as undamaged as possible.

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