In 1990, Hollywood released a film entitled Arachnophobia. The following is a short dialogue between Dr. Ross Jennings and Chris Collins, 2 characters in that film. Dr. Jennings: Chris, I'm scared to death. Collins: Yeah, we all are, but our brains secrete a neurotransmitter that enables us to deal (with it). Dr. Jennings: I don't think I have that particular neurotransmitter.

Arachnophobia is the abnormal or unreasonable fear of arachnids (any eight-legged animal including spiders, daddy-longlegs^*, ticks, mites, scorpions, and others) in general and spiders specifically. It is one of the most common phobias, affecting more than 50% of women and 10% of men, ranking just behind bees and wasps as the most feared arthropods. The purpose of this site, of course, is not to feed such fears. However, a European study recently determined that there are about 131 spiders, albeit most very small ones, per square meter (about 10³/₄ square feet) of the entire world.

There are over 3,000 kinds of spiders in the United States and about 60 of them have been implicated as causing medically significant bites to people. Yet, most spiders are completely harmless and are actually beneficial. The world’s spider population is estimated to consume 1,870,000,000 lbs. of insects daily, including a number of pests. To place this number in perspective, that’s equivalent to over 12,400,000, average-sized (150 lb.) people per day…perhaps a little gruesome to put in those terms, particularly when talking about spiders. But, you get the point. They have voracious appetites.

Spiders, in general, are very timid, and most spiders in the Midwest US are harmless to humans. About 80% of suspected “spider bites” are not caused by spiders at all but caused by other arthropods, including insects and ticks, by an unexplainable skin irritation or by an unrelated skin disease. The most common spiders in and around homes in this area include “hunters,” such as jumping spiders, wolf spiders, fishing spiders, sac spiders, crab spiders, and Parson (Gnaphosid) spiders; and “web-builders,” such as comb-footed (house or cobweb) spiders, orb (garden and barn) spiders, and grass spiders.

Yet, even these innocuous critters, when threatened, will defend themselves by biting the offender, human or otherwise. The reactions to such bites are typically mild, ranging from a nearly imperceptible pair of small puncture wounds to the development of a small sore, with various degrees of localized redness, swelling, itching, pain and tenderness, which may persist for a few days before resolving. Moreover, it is believed that yellow sac spiders, commonly found throughout the US, are responsible for more bites than any other spider, and their bites are often misdiagnosed as Brown Recluse bites.

Another less common spider, the Hobo spider, located in the western US and southwestern Canada, is also capable of a bite similar to, albeit less severe than the Brown Recluse. It is reported to be more aggressive, sometimes biting with little provocation. False Black Widow Spiders (Steatoda spp) inflict a venomous bite similar but less severe than their true counterparts. One of the two species, S. grossa, is found in the coastal states of the Atlantic, Gulf, and Pacific regions, while the other, S. borealis, is located in the northern US and southern Canada. Of course, who could forget the large, hairy, portentous-appearing tarantulas. Perhaps, however, it is their bristly hair that is likely to pose more of a problem than their bite, causing skin irritation and a hivelike reaction, especially in those maintaining tarantulas as pets. These rather timid critters are found naturally in the South and Southwest US, and their bite is typically equivalent to a bee sting and not considered dangerous unless the victim is allergic to tarantula venom.

A fair number of spiders worldwide are considered dangerous, whose bite may not only be very painful but whose venom may also elicit rather significant symptoms and potentially death. Thankfully, however, nearly all of them are not naturally found, and only a very few of them are rarely found, in the upper Midwest US. Furthermore, even these are rather docile in nature and do not bite unless provoked. If interested in learning more about dangerous spiders that are not naturally found in this area click here.

Venomous spiders in the US include sac spiders, Hobo Spiders and False Black Widow Spiders, already mentioned. Undeniably, however, the most venomous and, therefore, medically significant spiders in the US are Widow and Brown Recluse Spiders. There are five closely related Widows, including the Red Widow (Latrodectus bishopi), Brown widow (L. geometricus), Western black widow (L. hesperus), Southern black widow (L. mactans) and Northern black widow (L. variolus). While the other four Lactrodectus species are not typically found in the Midwest US, the Northern Widow Spider is infrequently found in this area. The Brown Recluse Spider is most commonly seen in the southern and central US and is uncommon in the upper Midwest. However, in April of last year, the Daily Mail Reporter reported that, because of climate change, the population of this spider was growing and was predicted to expand into the northern US. The table which follows gives the identifying characteristics of these spiders, their geographic range, habitat, the type of toxin secreted in their venom, and the symptoms of their bites.

Mild, localized, spider bite reactions should be treated appropriately. As is the case with other arthropod bites, allergic reactions of various severities can also occur with spider bites. If a more severe, allergic reaction, with tongue or throat swelling, wheezing or difficulty breathing occurs, or if the bite of either a Black Widow or Brown Recluse Spider is suspected, these are medical emergencies, immediate, rapid medical attention is recommended, and the aid of emergency medical responders must be initiated by calling the 911 or local equivalent emergency telephone system. Click here to be directed to the blog entitled, Bugs Be Gone - The Bugs of Summer, for further information. As similarly stated in previous Blogs, prevention of a spider bite is preferable to treating a bite itself. Vacuuming-up or crushing a spider with a shoe or rolled-up newspaper is most effective. Sticky traps may also work but should be placed where children or pets cannot tamper with them. Pyrethrin/amorphous silica gel-containing absorptive dusts can be applied outdoors by a professional pest control agent. Typical aerosol pesticide sprays are effective only if the spray lands directly on the spider.

________________________________________________________

Medically Significant Venomous Spiders in U.S.

SPIDER: Widow Spiders
IDENTIFYING CHARACTERISTICS: (Female spider only is venomous) Approximately ¹/₂-inch (~ 1.25 cm) length, cephalothorax and abdomen combined; Approximately 1¹/₂ inch (~ 4 cm) leg span. Shiny black body (Western, Southern and Northern Widows); Brown Widow usually lighter in color; tan to dark brown to black, with shades of grey also possible; Red Widow has red cephalothorax and dark red-brown to black abdomen. Orange-red (Brown Widow orange to yellow) marking on underside of the abdomen in shape of hourglass (Western and Southern widows), sometimes separated into 2 triangles; two red bars on underside and red bars on top of abdomen (Northern Widow); red hourglass or non-distinctive red mark on underside and orange and yellow spots on top of abdomen (Red Widow). Small fangs typically incapable of penetrating thick skin.
VARIETY, SCIENTIFIC NAME AND GEOGRAPHIC DISTRIBUTION:
Red Widow, Latrodectus bishopi, Florida;

Brown widow, L. geometricus, southern, southeastern and southwestern US;

Western black widow, L. hesperus, western US;

Southern black widow, L. mactans, throughout US but especially southeastern and southwestern
regions, Mexico and Canada

           Northern black widow, L. variolus, primarily northeastern US and southeastern Canada.
     HABITAT: Prefer dark, close quarters outdoors such as woodpiles or
     crevices under rocks. Found indoors in quiet locations such as basements,
     crawl spaces, and attics typically nesting in narrow gaps between walls and
     stored boxes or other object; under outdoor toilet seats. Nocturnal.
     TOXIN TYPE: Neurotoxin.
     SYMPTOMS: (Latrodectism) Bite typically painless; pain beginning within an
     hour, maximizing in 1 – 3 hours, with dull, numbing ache in and around bite site
     and pain in lymph nodes of groin or underarms, depending on location of bite;
     progressing to painful localized or generalized muscle cramps particularly in larger
     muscle groups, such as the back and abdomen, associated with elevated blood
     pressure, elevated heart rate, clammy skin, profuse sweating, weakness, and
     tremor; nausea and vomiting, difficulty breathing; chest pain, dizziness, faintness
     and seizures in more severe cases; death in 5% of untreated cases, mostly young
     children or adults in poor health.
     TREATMENT: Serious reactions, i.e. more than minor pain and/or the presence
     of whole-body symptoms, are a medical emergency and antivenom will be
     required along with narcotic analgesics.

SPIDER: Brown Recluse Spider (Loxosceles reclusa); AKA Fiddleback or Violin Spider.
IDENTIFYING CHARACTERISTICS: Nearly ¹/₂-inch (~ 1.25 cm) length, cephalothorax and abdomen combined; tan, dark brown, gray or deep-yellow colored, with fine, short hairs on abdomen; characteristic but not diagnostic violin pattern on dorsum of cephalothorax; most characteristic and identification dependent on finding 6 eyes in 3 pairs instead of typical eight eyes of most other spiders.
GEOGRAPHIC DISTRIBUTION: Southern Midwest, south of a line from southeastern Nebraska through southern Iowa, Illinois, and Indiana to southwestern Ohio, south to the Gulf of Mexico. However, expanding both in population and range further north. In the south, from central Texas to western Georgia, north to Virginia; also, very common in the northwest, particularly Washington State.
HABITAT: Synanthropic – Greek for together with (syn-) man (anthro), i.e. live near, and benefit from, an association with humans. Build webs in woodpiles, sheds, closets, garages, enclosed spaces, cellars, other dry, undisturbed places, favoring cardboard. Often encountered in shoes, inside dressers, in bed sheets of infrequently used beds, in clothes stacked or piled or left lying on the floor, inside work gloves, behind baseboards and pictures, in toilets, and near sources of warmth when ambient temperatures are lower than usual. Nocturnal hunters.
TOXIN TYPE: Hematoxin.
SYMPTOMS: (Loxoscelism) Bite typically painless but there may be an initial stinging sensation and most do not result in skin breakdown or systemic effects. However, in a small number (<10%), initial stinging is replaced in 6 – 8 hours by intense pain and itching, followed by the development of a blister and blue discoloration (cyanosis) at and surrounding the bite site, surrounded by blanching, which is itself surrounded by a large area of irregular redness – typical “red, white and blue” sign of recluse spider bite. After blister breaks, a large ulcer forms with the development and localized spread of skin and soft tissue necrosis and breakdown.
Rarely, systemic symptoms can occur, including fever, chills, nausea, vomiting, joint pain, seizures, hemolysis (break-up of red blood cells), disseminated intravascular coagulation (the development of blood clots throughout the body’s blood vessels with consumption of platelets and clotting factors resulting in abnormal hemorrhage), renal failure and coma.
TREATMENT: Depends on severity of reaction. First aid includes application of ice or cool compresses, elevation of area above level of heart if possible, wash area with cool water and soap, immobilization of affected area, and acetaminophen (Tylenol) for pain relief. Seek medical attention ASAP. A medication called Dapsone may be prescribed and excisional surgery with skin grafting may be required.

^{* Although daddy-longlegs are commonly referred to as “spiders” and have certain characteristics of spiders, they actually differ from true spiders in several ways, and their classification order is commonly referred to as “harvestmen” (Opiliones). As such, daddy longlegs appear to be more closely related to mites and, oddly, scorpions.}