Female black widows have shiny, spherical
abdomens, usually marked with a red hourglass shape on the ventral side. The
famous black widow is just one of the venomous widow spiders living throughout
the world. Bites from female widow spiders are medically significant, and may
require treatment with an antivenin. Widow spiders do not attack humans
unprovoked, but will bite when touched or threatened.
The Description: Most people will recognize
widow spiders by the hourglass markings on the underside of their abdomens. The
hourglass mark is not present in all Latrodectus species, however. Females take
longer to reach maturity and molt more times than males, resulting in darker,
shinier coloration. Males, by contrast, remain lighter and duller. Female widow spiders are larger than their
male counterparts; the body of a mature female measures about one half inch in
length. Female Latrodectus spiders have a spherical abdomen and long, thin
legs. Widow spiders belong to the cobweb
spider family. They spin irregular, sticky webs to catch insects. Like other
cobweb spiders, widows possess a row of bristles on their hind legs. This
"comb-foot" helps the widow spiders wrap her insect victims in silk.
Diet: Widow Spiders feed on insects, which they
capture in their webs. When an insect touches the web, the widow spider senses
the vibration and immediately rushes to capture the prey.
Life Cycle:
A female widow spider lays several hundred eggs, wraps them in a silken
egg case, and suspends it from her web. She keeps watch over the eggs, and will
defend them vigorously during the month of their development. During her
lifetime, the female may produce up to 15 egg sacs, with as many as 900 eggs in
each one. The newly hatched spiderlings
are cannibals, and will quickly devour one another until only a dozen or so
offspring remain. To disperse, the young spiders parachute down from the web on
silken threads. They continue to molt and grow for two or three months,
depending on their sex. Most females
live about nine months, but the male lifespan is considerably shorter. Widow
spiders, especially black widows, have earned a reputation for sexual
cannibalism – the female eats the male after mating. While this does
occasionally occur, it is more myth than fact. Not all males get eaten by their
partners.
Special Adaptations and Defenses: Widow Spiders do not have good eyesight.
Instead, they rely on their sensitivity to vibrations to detect prey or
potential threats. For this reason, it's never a good idea to touch the web of
a widow spider. A careless poke with a finger is likely to attract a speedy
bite from the resident widow.
Mature female Latrodectus spiders inject neurotoxic
venom when they bite. In prey, the venom takes affect fairly quickly; the
spider holds the insect firmly until it stops moving. Once the prey is
immobilized, the widow injects it with digestive enzymes that begin to liquefy
the meal. Though widow spiders are not
aggressive, they will bite defensively if touched. In humans, the venom causes
latrodectism, a medical syndrome that requires treatment. Within a few minutes,
a bite victim will feel localized pain at the site. Symptoms of a widow spider
bite include sweating, rigid abdominal muscles, hypertension, and swelling of
the lymph nodes.
Habitat: Widow
Spiders stay outdoors, for the most part. They live in crevices or recesses
within rock piles, logs, embankments, or outbuildings like sheds or barns.
Range: Widow
Spiders live on all continents except Antarctica. Worldwide, about 31 species
belong to this genus.
Facts: Widow
spiders are widely feared but poorly known. They are a medically important
group with a worldwide distribution. Most species favor xeric conditions. Some
species adapt well to human-altered conditions and are readily dispersed by
humans. They have remarkably diverse sexual biology involving cannibalism, mate
guarding, mating plugs, post-copulatory sterility, and varying degrees of sexual
size dimorphism.
There are currently 31 valid species of
Latrodectus. Widow spiders are most diverse in Argentina (7 species), the
Middle East (7 species), South Africa (76 species), and North America (5
species).
Characteristics:
The male palp is distinctive with a long spiral embolus. The female
genitalia feature an atrium and dumbbell-shaped sperm thecae (female sperm
storage organs). The famous red hourglass marking on the ventral part of the
abdomen is not present in all species.
Their Medical Importance: Black widow venom is a neurotoxin that can
cause latrodectism, a mild to severe medical syndrome. The bite itself is
usually not perceived but local pain may occur several minutes after the bite.
Typical symptoms include swelling of the lymphatic nodes, profuse sweating, and
rigidity of the abdominal muscles, facial contortions, and hypertension.
Antivenin is available to counteract the effects. Cases of latrodectism are
known from all geographic regions where widow spiders occur. Across the globe bites
appear to be patchy. Actual or alleged bites in the various geographic regions
are attributed to the various local widow species, which differ significantly
in toxicity, aggressiveness, and ecology.
One of the key factors influencing the
epidemiology of latrodectism is the ecology of local Latrodectus species.
Latrodectus tends to be urbanized in North America and Australia, while in
Argentina and the Mediterranean region, Latrodectus is more likely to be found in
rural or natural areas. In regions where
Latrodectus is not urbanized, latrodectism is often associated with farm
workers and summer months, when farming is most intensive. In regions with
urbanized Latrodectus species, latrodectism affects a broader cross section of
the population, and bites may occur at almost any time of the year.
Size: Latrodectus
spp. spiders are the largest of the Theridiidae (cobweb weaver) spiders. The
size of a Latrodectus can vary across species.
·
Adult females: 1/2-inch long, not including the
legs (about 1-1/2 inches when legs are spread).
·
Adult male: About half the female’s size, with
smaller bodies and proportionally longer legs.
Scientific Identification: An important
characteristic of the Latrodectus is its “comb foot.” The spider has a row of
strong, curved bristles on the hind pair of legs, which form a distinct comb.
The comb is used for flinging silk over its prey.
The Adult Female: The coloration of the spider
can vary by species (brown, black, red), but all females (of the species found
in the US and Canada) are shiny black, brown-black, or red with possibly a row
of red spots on the top of the abdomen along the midline. Two reddish triangles
resembling an hourglass are present on the underside of the abdomen of all
species except the Red Widow (L. bishopi). Females are sedentary, staying on or
near their web. They will bite if molested.
The Adult Male: Are harmless. The male’s abdomen usually has
red spots along the upper midline and white lines or bars radiating out to the
sides. Males almost exclusively wander in search of females.
Immature black widows: Of both genders are
harmless. Newly hatched spiders 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. The males
will mature faster, causing the spider to maintain more of its juvenile
coloration; whereas females mature slower, allowing the spider to obtain the darker,
shinier appearance.
Their Web:
These spiders are nocturnal and build a three-dimensional tangled web,
often with a conical tent of dense silk in a corner where the spider (female)
hides during the day.
The Species: There are five species of Latrodectus
in North America, which can generally be identified by location, markings
(style of hourglass), sometimes and coloration. The Southern Black Widow: Southern black
widows have a longer than wide second orange spot on the abdomen. The Northern
Black Widow: Northern black widows have a wider than long 2nd orange spot
The Range:
Throughout the US and Southern Canada. It is more common in the southern
and western US states. Black Widows are
not found on the mainland of Northwestern Washington. There have been a few
populations recorded from Whidbey Island and some of the San Juan Islands.
Their Habitat:
In nature, it is a fairly common spider; most species are found in
recesses under rocks, or logs in a woodpile, in crevices or holes in dirt embankments,
in dark sheltered spots, and in barns & outbuildings, where it builds
strong-walled retreats quite close to the ground. However, they readily adapt to human-altered
environments, and are most commonly found in outbuildings (sheds, barns, privies),
water meter holes, nursery cans, around lids of dust bins, around seats of
outdoor privies, spaces under chips of wood, around stacked materials of any
kind, in deserted animal burrows or rodent holes, entwined in grape arbors, and
under any item or structure (e.g., barbeque grill, slide, sand box) that has
been undisturbed for a lengthy period. Additionally, in the eastern US,
Latrodectus mactans is associated with littered areas, with dumps of large
cities, with garages, and storage sheds. In arid parts of Arizona, this spider
inhabits almost every crevice in the soil and its nests are found in cholla
cacti and agave plants.
CAUTION: This spider may also find its way into
clothing or shoes and occasionally seeks a spot in a house to build a web, but
it is usually not found indoors. When it does seek shelter in a building, it is
due to cold weather and a need for a dry shelter. For the Red Widow, the webs
are generally located 3' to 10' above the ground, (spiderlings and immature
spiders build their webs close to the ground) and the main area of the web can
extend up to 4' from the females retreat. It is basically a cobweb sheet with a
large number of snare lines extending upwards. Their prey flies into these
snares, and usually falls to the sheet. The widow then rushes out to make the
capture.
Food: They
typically prey on a variety of insects, but occasionally they do feed upon
other arachnids. When the prey is entangled by the web, the spider quickly
comes out of its retreat, punctures and poisons its prey. The poison takes
about 10 min. to take effect, meanwhile the prey is held tight by the spider.
When movements of the prey cease, digestive enzymes are released into the wound.
The black widow spider then carries its prey back to its retreat before
feeding.
Their Life Cycle: Black widows mature in two to four months. At
first the young appear white or yellowish, but with each molt their coloration
darkens. Until maturity both sexes resemble the male and are harmless to
humans. Females usually mature within 90 days, and live for another 180 days,
while males usually mature about 70 days and live only about a month longer.
Males generally require fewer molts to mature than females.
Reproduction:
Female black widows commonly lay about 400 (occasionally up to 900) eggs
in oval, papery sacs, about 1/2 inch long. A single female can produce nine egg
sacs in a summer. Eggs incubate for 20-30 days, after which the spiderlings
hatch; however, more than 12 rarely survive this process, due to cannibalism. The female black widow's notorious habit of
eating the male after mating is a misconception, but there are observed cases
where the female will consume the male during or after mating. This behavior
has actually been observed in many species of spiders other than just widows.
Females are nocturnal, shy and rarely leave their web, from which they hang,
belly upward. Males and females feed on insects and other arthropods and are
preyed upon by mud-dauber wasps.
Being Bitten:
Caution: Female Black Widow Spiders are very venomous, and can be
harmful to people. Bites occur most frequently when the spider is trapped
against human skin, either by reaching under objects where the spider is hiding
or when putting on clothing, gloves or shoes containing the spider. Widow
spiders are generally very timid and only bite in self-defense when they
accidentally contact humans. The bite from the widow spider causes a set of
symptoms in the bite victim known collectively as latrodectism. Latrodectism is
caused by the neurotoxic venom injected by the widow. The severity of a Latrodectus bite varies
with the species, the age and health of the victim, and the amount of venom
injected into the victim. The most severe bites have been reported to be from
the Southern Black Widow. The Brown Widow is suspected to have the least severe
bite (it is considered to possibly be medically insignificant). It is suspected
that the brown widow either is more hesitant to bite, or the amount of venom
injected (a process called envenomation) is less than the amount injected by
its cousins.
For the most part, the black widow's bite may be
felt only as a pin prick, during which the spider's fangs inject a minute
amount of highly toxic venom under the skin. The severity of the victim's
reaction depends on his or her age and health, and on the area of the body that
is bitten. Local swelling and redness at the site may be followed in one to
three hours by intense spasmodic pain, which can travel throughout the affected
limbs and body, settling in the abdomen and back (intense abdominal cramping,
described as similar to appendicitis), and can last 48 hours or longer. Elderly
patients or young children run a higher risk of severe reactions, but it is
rare for bites to result in death; only sixty-three has been reported in the US
between 1950 and 1959. Other symptoms can include nausea and profuse
perspiration. If left untreated, tremors, convulsions and unconsciousness may
result. When death does occur, it is due to suffocation.
Note: Male Black Widow Spiders (and the
juveniles of either gender) do not bite and are not dangerous; only bites from
the adult female present a medical concern.
If you are bitten by a Black Widow Spider: Contact
your physician, hospital or poison center immediately and follow their
instructions. Poison Centers across the country now have a new national
emergency phone number - 1-800-222-1222.
Collect the spider if possible for identification. Your physician may
administer an anti-venom treatment and calcium gluconate to alleviate pain, and
will probably treat the site with antiseptic to prevent infection. If you have a heart condition or are
otherwise vulnerable, you may require a hospital stay until symptoms subside.
Usually bite victims recover fully within two to five days.
Precautions:
Be very careful when working around areas where widow spiders may be
established. Take proper precautions-wear gloves and pay attention to where you
are working. The reaction to a widow bite can be painful, and the victim should
go to the doctor immediately for treatment.
Note:
This is the Third in a series that I am doing on Spiders, enjoy - Bird
