|
Black Widow Spider
HYG-2061A-97
William F. Lyon
| Common Name |
Scientific Name |
| Black Widow Spider |
Latrodectus mactans (Fabricius) |
| Northern Widow Spider |
Latrodectus variolus (Walckenaer) |
Both the black widow spider and northern widow spider are present in Ohio.
The black widow spider is found primarily in the southern Ohio counties whereas
the northern widow spider is found in the northern Ohio counties. Most occur
outdoors and are not aggressive unless confined or disturbed. Females are more
likely to bite when guarding an egg sac. Reports indicate that mortality from
bites is the result of one percent or less of the cases, usually occurring in
very young or very old individuals. With healthy people, recovery is usually
complete in 2 to 5 days. However, this spider is considered the most venomous
spider in North America.
Identification (click picture to enlarge)
Adult black widow spiders have shiny, jet black, rounded, globular abdomens
with two reddish or yellowish triangles on the underside which form a
characteristic hourglass marking. Adult female northern widow spiders are shiny
black or brown-black with two reddish triangles on the underside, resembling a
split hourglass. These spiders are about 1/2-inch long, not including the legs
(about 1-1/2 inches when legs are spread). Adult males are harmless, about half
the female's size, with smaller bodies, longer legs and usually have yellow and
red bands and spots over the back as do the immature stages. Newly hatched
spiderlings are predominately white or yellowish-white, gradually acquiring more
black and varying amounts of red and white with each molt. Juveniles of both
sexes resemble the male and are harmless.
Life Cycle and Habits
These spiders spin tangled webs of coarse silk in dark places, usually
outdoors. Webs are usually built near the ground (occasionally within dwellings)
normally in trash, rubble piles, under or around houses and outbuildings such as
privies, sheds and garages. The female lays eggs in silken cocoons or sacs which
are globular in shape and about 1/2-inch in diameter. Sacs are white at first,
later turning pale brown. About 300 to 400 eggs per sac is common with 4 to 9
egg sacs produced during a summer. Normally, only 1 to 12 young survive after
the egg incubation period of 14 to 30 days due to cannibalism.
Growth requires 2 to 4 months depending on availability of prey during which
the females molt 6 to 8 times and the males 3 to 6 times. Females mature 92 days
after egg sac emergence and live about 179 days longer, whereas males mature 71
days after emergence and live 30 days longer. Usually the female eats the male
after mating. However, if females are well fed, most males get away to mate
another day. Females hang belly upward, rarely leaving the web. Often cold
weather and drought may drive these spiders into buildings. Prey caught in the
web include a variety of insects (cockroaches and beetles) and other arthropods.
The northern widow spider is similar to the black widow except its habitat is
marginal land with sparse vegetation. It is found in stumps, hollow logs and
piles of debris (occasionally indoors). The female black widow is shy and
nocturnal in habit. She does not leave her hidden web voluntarily and is
completely out of her area when away from the web. Outbreaks of black widows
occur erratically. Some years an area may have thousands of widows and the next
year they may be gone. Certain kinds of habitats such as sand dune areas may
have black widows every year. Alternating warm and cold weather during the
winter and spring months are detrimental to survival.
Bite Symptoms
According to Willia Gertsch, curator of spiders at the American Museum of
Natural History, New York, the venom of the black widow spider is 15 times as
toxic as the venom of the prairie rattlesnake. However, only a minute amount of
the toxin is injected with a single bite by the spider, while the relatively
large amount of injected rattlesnake venom results in about 15 to 25 percent
mortality among those bitten.
The severity of a person's reaction to the bite depends on the area of the
body bitten, amount of venom injected, depth of bite, seasonal changes and
temperature. The bite feels like a pin prick or is not even felt. At first,
there may be only slight local swelling and two faint red spots surrounded by
local redness at the bite. Pain becomes intense in one to three hours and may
continue up to 48 hours. Pain usually progresses from the bitten member up or
down the arm or leg, finally localizing in the abdomen and back. The abdominal
muscles may become rigid and board-like with severe cramps (resembles
appendicitis). There may be pain in the muscles and soles of the feet, and
eyelids may become swollen. Other symptoms may be nausea, profuse perspiration,
tremors, labored breathing and speech, and vomiting. During this time, a feeble
pulse, cold clammy skin, unconsciousness, convulsions and even death may result
if the victim does not receive medical attention immediately. Additional
complications may occur due to the infection of the bite. However, with some
untreated individuals, symptoms may diminish in several hours and be gone in
several days after agony. Bites are uncommon and serious long-term complications
or death are rare. Only four deaths were officially attributed to black widow
bites in the United States from 1960-69.
First Aid
If bitten, remain calm, collect the spider, if possible, for positive
identification and get medical attention immediately. (Contact your physician,
hospital and/or Poison Information Center.) First aid is of limited help.
Application of a mild antiseptic such as iodine or hydrogen peroxide prevents
infection.
Persons younger than 16 and older than 60, especially those with a heart
condition, may require a hospital stay. (Health and lung failure may result in
death.) A physician can give specific antivenom or calcium gluconate to relieve
pain. Healthy people recover rapidly in two to five days.
Control Measures
The black widow spider is shy and nocturnal in habit, usually staying in her
hidden web. Although not aggressive, she may rush out and bite when her web is
disturbed or when accidentally trapped in clothing or shoes. Many are associated
with dry, undisturbed piles of firewood, old limbs, rock piles, bales of hay,
wooden buildings and pit privies.
Prevention
Remove trash, old boxes, piles of lumber, old rubble piles and other unwanted
items from under or around houses and outbuildings. Do not go barefoot or handle
firewood without gloves. Install screens on doors and windows to prevent entry.
Seal or caulk cracks and crevices where spiders can enter the house. Wash off
the outside of the house or building, especially around window wells and other
undisturbed places where webs are built. Spiders are fragile and easily damaged,
so sweeping with a stiff broom will remove webbing and usually kill them. (Use
Caution.)
Insecticides
Since black widow spiders spend most of the time in or on webbing, thorough
applications of fine particles of insecticides, such as ULV, aerosols or fogs,
contact spiders in their webs causing quicker population reduction. Although
pyrethrin is registered specifically for black widow spiders, other space sprays
of resmethrin (Vectrin) are useful for clean outs in outbuildings, crawl spaces,
etc.
There are many other labeled pesticides for spider control. Some are labeled
for homeowner use, while others are labeled only for the licensed, certified,
pesticide applicator or pest control operator. Homeowners can use amorphous
silica gel (Drione, Tri-Die), some formulations of bendiocarb (Ficam),
chlorpyrifos (Dursban), and permethrin (Astro, Dragnet, Flee, Prelude, Torpedo);
diazinon, esfenvalerate (Conquer), propoxur (Baygon), pyrethrin (Exciter,
Kicker, Microcare, Pyrethrum, Safer, Synerold, Uld, X-Clude) plus resmethrin (Vectrin).
In addition, the licensed pesticide applicator can use bendiocarb + pyrethrins (Ficam
Plus), clyfluthrin (Optem, Tempo), cypermethrin (Cyper-Active, Cynoff, Demon,
Vikor), deltamethrin (Delta Dust, Suspend), lambdacyhalothrin (Commodore),
propetamphos (Safrotin) and tralmoethrin (Saga).
Residual crack and crevice sprays of Diazinon or propoxur (Baygon) applied
where spiders can hide and enter buildings, are helpful.
Outdoors, spray around the perimeter of buildings using formulations that
will not damage plants. Treat under patios and decks if the house is of pier and
beam construction. Baygon, Diazinon, Drion and Permethrin are frequently used.
Before using any pesticide, always read the label and follow directions and
safety precautions.
Click here to buy concentrated pyrethrins
EXCITER Pyrethrin Concentrate
An emulsifiable, synergized
Pyrethrin spray. This concentrate (4 ounces per gallon) of 6% pyrethrum can
be mixed in water or oil. It will provide a quick knockdown of
flies, ants, and most every
insect. It can be applied directly on dogs @ 1 to 2.125 oz. per gallon. One
pint of concentrate can make up to 16 gallons of ready to use product.
It is most commonly used in a fogging machine as a space spray.
Pyrethrum is a natural pesticide which provides a quick kill but no
residual. Pyrethrum will work well on any flying
insect including flies. You may use as little as one ounce per gallon or as
much as 4 ounces per gallon. Limited supplies due to worldwide shortage.
See Label See MSDS for
product information
CANNOT
BE SHIPPED TO NEW YORK.
(item no. 29.0139.23)
| Ohioline | Search
| Factsheets/Bulletins
| Ordering
Info |
|
Toll
Free voice line 1877-207-9640
