Geographic Range
Westerm black widow spiders,
Latrodectus hesperus
, live in the warmer regions of the United States. This species can be found in all
four of the deserts of the American southwest.
Habitat
Black widow spiders live under ledges, rocks, plants, and different types of debris.
Webs are usually built near to the ground. Webs are sometimes built inside trash cans,
piles of trash, as well as under or around houses. When the weather changes from warm
to cold, black widows are most likely to find places inside of homes in which to live
or spin their webs. in order to prevent black widows from invaiding a home, home owners
should remove materials where these animals can hide. If a person happens to find
an egg sac, it should be removed with an object other than one's hand.
- Habitat Regions
- temperate
- terrestrial
- Terrestrial Biomes
- desert or dune
- Other Habitat Features
- urban
- suburban
- agricultural
Physical Description
Adult female black widow spiders are usually black and shiny. Black widows are most commonly recognized because of the reddish hourglass shape on the underside of the abdomen. Females measure an average of 3.5 cm in length, and typically have a very round abdomen.
Adult males are half the size of females. Their bodies are smaller, but they have longer legs than the females. Males have yellow and red bands and spots dorsally.
Newly hatched black widows are white, but can sometimes be a yellowish-white. As they
get older, they slowly turn black. Mature black widows can vary in the amounts of
red and white on their bodies.
- Other Physical Features
- ectothermic
- bilateral symmetry
- poisonous
- Sexual Dimorphism
- female larger
- sexes colored or patterned differently
Reproduction
Adult male black widows wander around in search of a female. During this time, males do not bite or feed. First, a male black widow spins a very small web, and then he places a drop of sperm on the web or the silk. He then takes the sperm into special receptacles on the ends of his pedipalps. Afterwards, he searches for a female so that he can place the sperm into the female's genital opening. After the female and male mate in this way, the female lays several bunches of eggs, which contain about 750 eggs. A single bunch of eggs is suspended in a web so that nothing happens to to the eggs before they hatch. A single egg case is about 1 cm in diameter. The egg sac can either be tan or white, and usually has a paper-like texture. Within a given summer, a female may make between 4 and 9 egg sacs. Incubation lasts about 14 days, and the young spiders are cannabalistic. Only one to twelve spiders from an egg sac actually live to be 30 days old.
After males are born, it takes about 70 days for them to mature, and then they die
after about a month to two months. In part, this is because females sometimes eat
a male after mating takes place. Females, on the other hand, only take about 90 days
to mature. Female black widows usually live up to a year and a half.
- Key Reproductive Features
- gonochoric/gonochoristic/dioecious (sexes separate)
- sexual
- fertilization
- oviparous
Lifespan/Longevity
Males live only a couple of months after reaching maturity. Females can live up to
a year after reaching maturity.
Behavior
Western black widow spiders spin webs that do not take on a definite shape or form. The webs vary in location, but more so in appearance. The silk that creates the web is made up of a liquid from the large abdominal glands. The glands open on the surface of the black widow's abdomen at the spinnerets. As the silk comes outside of the abdomen, it solidifies becuase of the stretching. Black widow silk is stronger than any other arachnid's.
These spiders are shy and nocturnal, and usually stay hidden inside of the web unless frightened. The belly is always facing the upward position. If a black widow is hidden inside a shoe, for example, and a person puts his/her foot inside of the shoe, the black widow will most likely bite. Females are not agressive, but will bite if disturbed.
These spiders produce a potent venom to which humans react, although the incidence
of death from a black widow bite is actually quite small.
Food Habits
Western black widows are like most arachnids in that they feed primarily on insects. Because of sticky substances in the silk of a web, black widows are able to catch their prey. The web is made of coarse silk.
The diet of
L. hesperus
includes beetles, cockroaches, and flies. Black widows kill by means of very small,
hollow fangs through which they inject a poisionous venom into their prey. Black widows
make small punctures all over the body of their prey, and then proceed to suck out
the liquid contents. Because the black widows only take food in the form of liquid,
the insect is not fully digested. However, digestive juices of the spider are injected
into the insect prey, helping to make more of the prey item edible to the spider.
Black widows leave behind the external skeleton of prey insects. These empty shells
can be seen near the spider's web. A female black widow may occasionally cannibalize
males of the species after mating.
- Primary Diet
- carnivore
- Animal Foods
- body fluids
- insects
- terrestrial non-insect arthropods
Predation
Economic Importance for Humans: Positive
Black widow spiders are not really beneficial to humans except for the fact that they
eat insects. Western black widows are often found around human habitations, which
makes them a potential predator of pest insects.
- Positive Impacts
- controls pest population
Economic Importance for Humans: Negative
Black widow spiders can be dangerous animals. They have a poisionous venom that is
fifteen times as toxic as a rattlesnake. When a spider bites, only a little bit of
the venom is injected into the prey. Rattlesnakes are considered more dangerous becuase
when they bite, more of the venom is injected into their victim. However, it is important
to note that if a large amount of the venom created by the black widow were to get
into a human, that person would most likely die. In spite of this, most bites are
not fatal. The bite of the black widow is more likely to be painful, and it can cause
internal problems. Such side effects include abdominal pain as well as swelling of
the muscles in the feet. The more mild symptoms include dry mouth, increased sweating,
and swollen eyelids. If a person younger than 16 or older than 60 is bitten, he/she
might have to go to the hospital. Most times death from black widow bites results
in people between these age ranges because of lung or heart failure. Healthy people
who are bitten usually recover in two to five days with the proper care. When a person
is first bitten, soap and water works well to clean the area, and one should also
apply a cold compress on the bitten area.
- Negative Impacts
-
injures humans
- bites or stings
- venomous
- household pest
Conservation Status
Latrodectus hesperus
is not an endangered species. These spiders can produce large numbers of offspring,
and people do not hunt them.
Other Comments
The most well known species of the black widow spider is Latrodectus mactans . The latin name means "murderous biting robber." This species occupies most southern areas. Latrodectus variolus is found in extreme parts of southeastern Canada. They live throughout the New England states and parts of Flordia. Latrodectus bishopi is also called a red widow. Brown widows, Latrodectus geometricus , are found in tropical areas. When this spider bites, it is not as severe as the other species of widows. The subspecies Latrodectus mactans tredecimguttatus is also known as a European black widow. Redback spiders, Latrodectus mactans hasselti , are found throughout Australia and some Southeast Asian countries.
When a woman's husband dies, she is called a widow. These spiders receive their common
name, "widows" because females sometimes kill their mates.
Additional Links
Contributors
Nancy Shefferly (editor), Animal Diversity Web.
Ashley Minus (author), University of Michigan-Ann Arbor, Phil Myers (editor), Museum of Zoology, University of Michigan-Ann Arbor.
- Nearctic
-
living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- temperate
-
that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).
- terrestrial
-
Living on the ground.
- desert or dunes
-
in deserts low (less than 30 cm per year) and unpredictable rainfall results in landscapes dominated by plants and animals adapted to aridity. Vegetation is typically sparse, though spectacular blooms may occur following rain. Deserts can be cold or warm and daily temperates typically fluctuate. In dune areas vegetation is also sparse and conditions are dry. This is because sand does not hold water well so little is available to plants. In dunes near seas and oceans this is compounded by the influence of salt in the air and soil. Salt limits the ability of plants to take up water through their roots.
- urban
-
living in cities and large towns, landscapes dominated by human structures and activity.
- suburban
-
living in residential areas on the outskirts of large cities or towns.
- agricultural
-
living in landscapes dominated by human agriculture.
- ectothermic
-
animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature
- bilateral symmetry
-
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
- poisonous
-
an animal which has a substance capable of killing, injuring, or impairing other animals through its chemical action (for example, the skin of poison dart frogs).
- sexual
-
reproduction that includes combining the genetic contribution of two individuals, a male and a female
- fertilization
-
union of egg and spermatozoan
- internal fertilization
-
fertilization takes place within the female's body
- oviparous
-
reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.
- diurnal
-
- active during the day, 2. lasting for one day.
- motile
-
having the capacity to move from one place to another.
- sedentary
-
remains in the same area
- solitary
-
lives alone
- venomous
-
an animal which has an organ capable of injecting a poisonous substance into a wound (for example, scorpions, jellyfish, and rattlesnakes).
- carnivore
-
an animal that mainly eats meat
- insectivore
-
An animal that eats mainly insects or spiders.
References
Bisacre, M., R. Carlisle, D. Robertson, J. Ruck. 1979. The Ilustrated Encyclopedia of Plants and Animals . New York: Exter Books.
Desert USA, 1996. "Black Widow Spiders/Latrodectus hesperus" (On-line). Accessed March 21, 2001 at http://www.desertusa.com/july97/du_bwindow.html .
Encyclopedia Britanica, 1999-2000. "Black Widow" (On-line). Accessed March 21, 2001 at http://www.britanica.com/b.../0,5716,15726+1+15522,00.html?query=latrodectus%20hesperu .
Jones, S. 1991. "Ohio State University Extension Factsheet/ Black Widow Spider" (On-line). Accessed February 15, 2005 at http://ohioline.osu.edu/hyg-fact/2000/2061A.html .
Vest, D., Eagle Rock Research. 1999. "The Widow Spiders" (On-line). Accessed March 23, 2001 at http://hobospider.org/widows.html .
Virtual Science Centre, 1996. "Latrodectus Hesperus" (On-line). Accessed March 21, 2001 at http://www.sci-ctr.edu.sg/events/exhibit/megabugs/blackwid.html .