Spider BitesDr. Jorge Parada
- National Pest Management Association
Monday, November 5, 2012
Harry Potter's friend, Ron Weasley, is probably in good company
when he admits he hates spiders. But how much of spiders' negative
notoriety is really just a bad rap?
In truth, spiders are not intentionally harmful to
humans. Most spider bites occur when humans accidentally trap or
brush up against a spider and receive a defensive bite. On rare
occasions, spiders may have a serious lapse in judgment and bite a
human finger (or other body part) mistaking it for a caterpillar or
other such prey. Even then, most spiders are too small and not
capable of breaking the skin with their fangs, or their venom too
weak to be dangerous to humans. Simply put - most spider bites are
accidental, harmless and require no specific treatment.
Still, that is not enough to stop spiders from having a bad
reputation. It is common for any unexplained skin irritation to be
called a "spider bite." In fact, most skin lesions and symptoms
that are attributed to spiders are rarely actually due to a spider
bite. Research has shown that 80 percent of presumed spider bites
are actually bites from other insects, or due to skin infections
such as MRSA (a resistant staph infection).
Yet, occasionally, a spider's bites will cause real harm. Spider
bites may cause injury by three mechanisms. First, especially with
larger spiders, the bite itself may be painful and cause injury.
However, far more concerning is the spider's venom,
which can include necrotic agents or neurotoxins. Spider bites
rarely transmit infectious diseases.
Most spider bites are less painful than a bee sting. Pain from
non-venomous spider bites typically lasts for five to
60 minutes while pain from venomous spider bites frequently
lasts for longer than 24 hours. The rate of a bacterial
infection due to a spider bite is low (less than one
The two spiders of greatest concern in the United States are the
recluse and the black widow
spiders, most commonly found in southern states. Both species
prefer warm climates and dark, dry places. Typically, these are
timid, non-aggressive spiders, often found in dry, littered,
undisturbed areas such as closets, woodpiles and under sinks.
Black widow spiders: Black widow spiders can be
found throughout North America, but are most common in the southern
and western areas of the United States. Male widows, like most
spider species, are much smaller and generally less dangerous than
the females. Widows tend to be non-aggressive, but will bite if the
web is disturbed and the spider feels threatened. The more
dangerous female is a dark colored spider and with a red hourglass
marking on its belly. The bite feels like a pinprick, and at first
may go unnoticed or seem rather minor. Early on there may be slight
swelling and faint red marks. Within a few hours, though, intense
pain and stiffness begin. Other signs and symptoms include: chills,
fever, muscle cramps, and gastrointestinal symptoms such as nausea,
vomiting and severe abdominal pain. Typically, black widow bites
are less common, but more severe than brown recluse bites. That
said, no one in the United States has died from a black widow
spider bite in more than 10 years.
Brown recluse spiders: The brown recluse
spider, also known as the violin spider, is most commonly found in
the south-central, mid-western and southern states of the United
States. Most encounters with this spider occur from moving boxes or
rooting about in closets, attics, garages or under beds where they
may have nested. These spiders are brown in color with a
characteristic dark violin-shaped (or fiddle-shaped) marking on its
head. Whereas most spiders have eight eyes, brown recluses have six
equal-sized eyes. The bite produces a mild stinging, followed by
local redness and intense pain within eight hours. A fluid-filled
blister forms at the site and then sloughs off to leave a deep,
enlarging ulcer. Systemic (or generalized) reactions from a brown
recluse spider bite vary from a mild fever and rash to nausea and
listlessness. Generally, brown recluse spider bites are reported
much more frequently than black widow bites, but while the brown
recluse bite may cause very significant local skin reactions, it is
much more unusual for these bites to cause generalized symptoms.
Unfortunately, brown recluses are almost communal and can be
sometimes be found in great numbers.
- If you suspect a spider has bitten you, try to bring it with
you to the doctor so they can determine the best course of
treatment based on the species.
- Clean the site of the spider bite well with soap and
- Apply a cool compress over the spider bite location (using a
cloth dampened with cold water or filled with ice).
- If you suspect the bite is from a black widow or brown recluse
spider, and the bite is on an extremity, elevate it.
- Consider tying a snug bandage above the bite and elevate the
limb to help slow or halt the venom's spread. Ensure that the
bandage is not so tight that it cuts off circulation in your arm or
- Adults can take aspirin or acetaminophen and antihistamines to
relieve minor signs and symptoms (but use caution when giving
aspirin to children or teenagers).
- Seek medical attention for any severe signs and symptoms, or if
signs and symptoms continue to worsen for more than 24 hours.
If a local reaction continues to get worse for more than 24
hours, it may be time to seek medical attention. Look for redness
spreading away from the bite, drainage from the bite, increase in
pain, numbness/tingling, or a discoloration around the bite that
looks like a halo or bull's-eye. If generalized symptoms set in, be
concerned. In very rare cases, there have been reports of spider
bites (by spiders considered otherwise harmless) causing allergic reactions - including anaphylactic shock, a life-threatening
condition (much like may result from the sting of a bee, or wasp in a
highly allergic person).
Contact a pest
professional if you think you may be dealing with a spider
infestation. To learn more about different types of spiders and the
threats they pose to our health, check out our spider Pest Guide
section or watch this Health Checks video on spider
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