I have been bitten by a spider, and I can tell you that what most people think is a spider bite, isn’t. A little itchy red bump – that’s not a spider bite; that’s a mosquito bite. How about a white, searing hot, prickly bump the size of a tennis ball? Yeah, that sounds about right. Here’s what you should do if you’ve been bitten.
If I got an itchy red bump on my skin that felt like a mosquito bite, but it was the middle of winter and I couldn’t remember being bitten, people would invariably tell me, “Oh, it’s just a spider bite. No big deal.” I never believed them, and you shouldn’t either.
First of all, the vast majority of spiders have fangs that are too small or too soft to penetrate human skin to any noticeable degree. For this reason, most people don’t know that a spider has bitten them. Second, spiders often have two biting styles: food-getting bites and defensive bites. The defensive bites usually happen too quickly to inject venom. Venom is the cause of the reaction, and most of what causes pain. So, if you can conclusively say that a spider has bitten you because you’re experiencing a reaction to it, accompanied by pain, it is a “big deal.” There are over 200 species of spiders in North America which are considered potentially dangerous, 60 in the US (4). The three species most commonly implicated in serious bites are black widows, brown recluses, and hobo spiders (1). Though not numerous, deaths have occurred from bites of all three of these spiders.
While the venoms of most individual species of spiders have not been extensively studied, the venoms of the black widow and brown recluse have been analyzed. Black widow venom contains a neurotoxin, which means that enough of it will paralyze the autonomically controlled muscles of the body, such as those involved in breathing, swallowing and heart rate. Without those functions, and without early detection and treatment, death is imminent. (This is why it is imperative to see a doctor immediately if you have been bitten by something and experience any of the symptoms of widow envenoming, which I will get to shortly). In the case of the brown recluse’s venom, the venom contains a necrotic agent, which means it kills tissues that it comes into contact with. However, as stated above, these are only 2 of 200 species of spiders in North America alone which can be dangerous. The hobo spider (also known as the aggressive house spider, species name Tegenaria agrestis) is one brown-colored spider which is often confused with the brown recluse, a dangerous mistake. The bites of both of these spiders create an ulcerous lesion at the site of the bite.
Systemic arachnidism is the poisoning of the entire body by spider venom. Many spider bites, especially those that are treated early, do not become this serious. By contrast, they are localized, meaning the venom only reached the tissues immediately surrounding the bite.
The venom, anatomy and physiology of all those spiders vary, and consequently the signs and symptoms of envenomation will vary depending on the offending critter. At this point, it would be wise to offer an approach to each spider individually, and then deal with general tips for the recognition and treatment serious bites.
The Black Widow
Everybody has heard of the black widow spider, and most people can recognize the signature red hourglass. So, I won’t go into too much detail here. Here are the quick facts on black widows:
Location: Black Widow spiders inhabit warmer regions of the world to latitude of about 45 degrees N. and S. There are several species of black widow, and so a different species will be found in California than in, say, Florida. But one species or another is found in all parts of the US.
Web & Behavior: The black widow web is irregular, showing no pattern, but the strands are stronger than that of all other spiders’ webs. The female black widow hangs upside-down and rarely leaves the web, which is why she is the most often seen and is also easily recognized. They are shy and nocturnal, and not aggressive. However, they may rush and bite if the web is disturbed or when accidentally trapped in clothing. The most often locate themselves outside, on the underside of ledges, rocks, plants and debris, but could be anywhere. Cold weather and drought may drive these spiders into buildings (6). The black widow, unlike the hobo spider, doesn’t have to attack its prey. Once the prey has exhausted itself in entanglement, it makes small punctures in its victim’s body and sucks out the liquid contents.
Appearance: The female is glossy black, with a blood-red hourglass shape on the underside of her abdomen. Her body is about 1.5 inches long. Adult males are harmless, half as big as females, with smaller bodies, and longer legs. The male is marked by four pairs of red marks along the sides of the abdomen.
Symptoms: The black widow’s venom is 15 times more toxic than rattlesnake venom. The bite itself is sometimes painless and may go unnoticed. Here are the symptoms of Black Widow systemic envenomation:
* Dull, numbing pain following the bite
* Cramping & muscular stiffness in the chest, back, shoulders and abdomen
* Alternating salivation and dry-mouth
* Breathing difficulty
* Profuse sweating
* Weakness
* Nausea and vomiting
Treatment: Antivenin is available, and either that or calcium gluconate can be prescribed to relieve pain. Most people recover in two to five days. For immunocompromised people, elderly, and children, clean the site well with soap and water. Apply a cool compress over the bite location and keep the affected limb elevated to about heart level (but not above). Aspirin or Tylenol may be used to relieve minor pain and swelling, and muscle relaxants can be given to reduce cramping. Hospitalization may be required for children less than 5 years old or for adults with severe symptoms.
The Brown Recluse
Location: The brown recluse spider is most common in the western and southern United States. It is often found under stones or in the dark corners of buildings.
Web & Behavior: The brown recluse spider just as shy as the black widow, and only bites humans when trapped in clothing or rolled onto when people sleep in bed.
Appearance: They are pale-colored and about 7mm long, with a leg span of about 2.5cm (1 inch) and a dark violin-shaped design on the back of its thorax.
Symptoms: Pain does not usually occur with the bite, and not for 2-3 hours afterwards. The location of the bite will blister, with intense localized pain and tissue necrosis, as the area becomes ulcerous. A brown recluse bite may go unnoticed for 6-8 hours before any reddening, swelling or blistering of the wound starts to appear. The area around the bite may become red, painful and itchy. The occurrence of additional symptoms depends upon the amount of venom injected by the spider. A severe bite can produce a necrotic lesion that may require surgery.
Diagnosis: The venom destroys the walls of the blood vessels near the site of the bite and causes a skin ulcer several inches in diameter. Differential diagnosis between brown recluse bite and hobo spider bite depends upon geography; symptoms are extremely similar, but there are areas where only recluses are found, and not hobo spiders (and vice versa).
Treatment: Although an antidote for brown recluse venom has been developed, it is not widely available and it appears to be most effective before the lesion develops. Antibiotics may be used successfully to control the ulceration without surgery. Prompt medical attention is critical to successful treatment of the bite.
The Hobo Spider
Location: The hobo spider is actually native to Europe, suspected to have been introduced into the ports of Seattle, Washington, in the 1920′s or ’30′s. It is currently found in all states west of the Rocky Mountains, and as far north as Alaska. High level of hobo activity has occurred in Washington, Oregon, Idaho, Montana, Wyoming, Utah, Colorado, Southern British Columbia. Some hobos have been identified in the Mid-West and North-Eastern US.
Web & Behavior: Hobo spiders build funnel-shaped webs in dark, moist areas. Hobo spiders especially like woodpiles. If you have a wood burning fireplace, be sure to brush off any spider webs before bringing firewood into the house. Keep your woodpiles away from the house. Compared to other species, the hobo spider’s webs are not very sticky. Food which lands in the web does not get stuck; instead, the vibrations alert the hobo spider which is hiding inside the funnel, and it quickly runs out and attacks its victim. Because this is how it eats, it must be very fast (up to 1 m/second) and aggressive, which explains why it appears to be more aggressive towards humans than most spider species (1, 2).
Hobo spiders very rarely climb vertical surfaces and are uncommon above basements or ground level. They are not good climbers, although they’ve been known to do it. They are commonly found in bathtubs because they found a way in but were unable to scale the slick sides of the tub to get out.
Appearance: Hobo spiders are moderately large (7-14 mm body length; 27-45 mm leg span). They brown overall, with no rings or markings of any kind on their legs. However, their bodies are marked with gray or pale brown marking.
The one on the left is male, which is more venomous than the female (on the right). While all kinds of hobo spiders are dangerous, you may like to know how to identify a male. The male has long “palps” that look like boxing gloves coming out of its front end. The abdomen of the male is also smaller than that of the female.
Symptoms: Bear in mind that up to 50% of hobo bites are dry, meaning that no venom was injected. These bites are not included. The hobo bite is often painless but can produce a slight prickling sensation. Migraine headaches often occur in this kind of spider bite. A small area of induration (hardened tissue) may occur around the bite at a diameter up to 15 centimeters (almost 6 inches) in the first 30 minutes after the bite. This hard area can be white or red and may expand gradually. After half a day or a day-and-a-half the point of the bite blisters, and a day later, the blisters may break and weep. It scabs over, but tissues beneath the scab continue to die (spreading necrosis). The ulcer can be as much as an inch across.
A word on necrosis: the hobo’s venom, as well as any kind of necrotic venom, causes immediate and severe coagulation of blood around the bite, causing oxygen deprivation in the tissues at the middle. This is the precise mechanism by which the venom causes tissue death.
Diagnosis: Conclusive diagnosis is virtually impossible without the culprit. Hobo bites are necrotic, just like the bite of the brown recluse. However, there are many places where only one or the other spider lives (i.e., hobos are more common in the West, and brown recluses are not found there at all), so diagnosis is inferred from location and symptoms.
Treatment: Surgical repair is sometimes needed, but permanent scarring is very common. Hobo spider bites generally require only local wound cleaning, topical antibiotics and tetanus prophylaxis to control the open wound.
First Aid for Most Spider Bites
According to the CDC, “optimal treatment for necrotic spider bites is not well defined” (1). In other words, because the spider is rarely recovered, and spiders and their bites are so various, it is difficult to say what will work for all spider bites, especially necrotic ones. Treatment for spider bites is usually symptomatic, meaning that all they can really do is treat the symptoms, not the poisoning itself.
* Find out if the victim saw what bit them, and have someone else track it down and capture it (Be sure to do this with gloves on, and secure the spider in a glass jar from which it can’t escape!)
* Wash the area of the bite with soap and water and apply a cold compress (an artificial cold pack, an ice pack, or even a bag of frozen peas or corn will do). The cold will control both pain and itching.
* Find out if the victim is experiencing the following:
o Severe dizziness
o Fainting
o Trouble Breathing
o Nausea
o Vomiting
o Trouble Swallowing
If the answer to any of these is “yes,” take them (and their little attacker when possible) to the hospital immediately.
If the answers to those questions is “no,” then the bite is not systemic or life-threatening. Oral antihistamines like Benadryl can be taken to control the swelling, itching and burning (all of which are also characteristic of any kind of allergic reaction). NSAIDs can be taken for pain. If the area is not too sensitive to touch and the skin is not ulcerous, calamine lotion or topical steroid cream can be used to relieve itching.
If your bite doesn’t appear serious and you decide not to seek medical attention, watch for the following over the next couple of days:
o No improvement within 3 days
o Any infection developing
o A peculiar rash appearing
See a doctor if any of these things occur.
Case Study
Up for a little medical sleuthing? Remember I said I had been bitten? Here’s what I experienced. You can draw your own conclusions about what bit me.
Location: Indoors in southern British Columbia, Canada.
Spider: Unidentified.
Incident: Experienced an extremely sharp, stinging/pinching pain just underneath the sleeve of my t-shirt in the middle of my bicep. Immediately pulled back the sleeve, but found nothing. Immediately removed my shirt and shook it out, but still couldn’t see anything.
Symptoms: Inspection of the bite revealed a tiny but deep purplish-red pinprick which hurt to touch. A hard, white area around the miniscule bite mark began to spread and swell. The area was hard as a rock, and within 20 minutes had become 3 inches in diameter and raised above the usual surface of my arm by at least a centimeter. The slightest pressure on any part of this hard area caused deep, spasmodic prickling pains throughout the entire area. The entire area was burning hot, even to the touch. I had to keep ice on it constantly, even while driving to get help. The area remained swollen for three days, gradually decreasing in diameter.
Treatment: After consulting with a doctor, “spider envenomation, vector unknown” was the diagnosis. I was instructed to keep ice on it until I was comfortable without it, and to take oral antihistamines. It was 24 hours before I could do without the ice at all times.
This was not a pleasant experience, especially when it didn’t seem to get better very quickly, and they told me they couldn’t do much for me. I was lucky; the poison was localized. If you are bitten, just remember the warning signs of systemic arachnidism, and seek help if you are at all concerned.
