Spiders are the largest group of arachnids. There are more than 35,000 species throughout the world that are named including 3,000 in North America. There are hundreds more that have not yet been identified. They are all predators and live on plants, in trees, under rocks, on the ground and water.
A spider's eyes are on top and near the front of its head. The size, number, and position of the eyes vary among different species. Most species have 8 eyes, arranged in 2 rows of 4 each. Other kinds have 6, 4, or 2 eyes. Some spiders have better vision than others. For example, hunting spiders have good eyesight at short distances. Their eyesight emables them to form images of their prey and mate. Web-building spiders have poor eyesight. Their eyes are used for detecting changes in light. Some species of spiders that live in caves or other dark places have no eyesight at all.
A spider's mouth opening is bellow its eyes. Spiders do not have chewing mouth parts, and they eat only liquids. Various appendages around the mouth opening form a short "straw" through which the spider sucks the body fluid of its victim.
The spider can eat some of the solid tissue of its prey by
predigesting it. To do this, the spider sprays digestive juices on the tissue. By
predigesting and sucking, a large tarantula can reduce a mouse to a small pile of hair and
bones in about 36 hours.
Chelicerae are a pair of appendages that the spider uses to seize and kill its prey. The chelicerae are above the mouth opening and just below the spider's eyes. Each chelicera ends in a hard, hollow, pointed claw, and these claws are the spider's fangs.
An opening in the tip of the fang connects with the poison
glands. When a spider stabs an insect with its chelicerae, poison flows into the wound and
paralyzes or kills the victim.
The fangs of tarantulas point straight down from the head, and the poison glands are in the chelicerae. In true spiders, the fangs point crosswise, and the poison glands extend back into the cephalothorax. Spiders also crush thier prey with their chelicerae. Some species use their chelicerae to dig burrows in the ground as nests.
Pedipalpi are a pair of appendages that look like small legs. One pedipalp is attached to each side of the spider's mouth, and they form the sides of the mouth. Each pedipalp has six segments (parts). In most kinds of spiders, the segment closest to the body bears a sharp plate with jagged edges. The spider uses this plate to cut and crush its food. In adult male spiders, the last segment of each pedipalp bears a reproductive organ.
A spider has 4 pairs of legs, which are attached to its cephalothorax. Each leg has 7 segments. In most kinds of spiders, the tip of the last segment has 2 or 3 claws. A pad of hairs called a scopula may surround the claws. The scopula sticks to smooth surfaces and helps the spider walk on ceilings and walls. Each leg is also covered with sensitive bristiles that serve as organs of touch and perhaps organs of smell. Some bristles pick up vibrations from the ground or air, or the spider's leg. Others detect chemicals in the environment.
Mabel Orchard Spider
When a spider walks, the first and third leg on one side of its body move with the second and forth leg on the other side. Muscles in the legs make the legs bend at the joints. But spiders have no muscles to extend their legs. The pressure of the blood in their bodies makes their legs extend. If a spider's body does not contain enough fluids, its blood pressure drops. The legs draw up under the body, and the animal cannot walk.
This picture was taken by our good friend Paul Oliver. Any reproduction is not permitted without our permission.
Spinnerets are short, fingerlike organs with which the spider spins silk. They are attached to the rear of the abdomen. Most kinds of spiders have 6 spinnerets, but some have 4 or 2. The tip of a spinneret is called the spinning field.
The surface of each spinning field is covered by as many as a
hundred spinning tubes. Through these tubes, liquid silk flows from silk glands in the
spider's abdomen to the outside of its body. The silk then hardens into a thread.
Spiders have 2 kinds of breathing organs-tracheae and book lungs . Tracheae, found in almost all kinds of true spiders, are small tubes which carry air to the body tissues. Air enters the tubes through 1 or, rarely, 2 spiracles. A spiracles is an opening in front of the spinnerets in most true spiders.
Book lungs are in cavities in the spider's abdomen. Air enters the cavities through a tiny slit on each side and near the front of the abdomen. Each lung consist of 15 or more thin, flat folds of tissue arranged like the blood vessels. As air circulates between the sheets, oxygen passes into the blood. Tarantulas have two pairs of book lungs. Most true spiders have 1 pair.
The blood of spiders contains many pale blood cells and is slightly bluish in color. The heart, a long, slender tube in the abdomen, pumps the blood to all parts of the body. The blood returns to the heart through open passsages instead of closed tubes, such as those of the human body. If the spider's skin is broken, the blood quickly drains from its body.
A digestive tube extends the length of the spiders body. In the cephalothorax, the tube is larger and forms a sucking stomach. When the stomach's powerful muscles contract, the size of the stomach increases. This causes a strong sucking action that pulls the food through the stomach into the intestine. Juices in the digestive tube break the liquid food into molecules small enough to pass through the walls of the intestine into the blood. The food is then distributed to all parts of the body. Food is also pulled through the stomach into a fingerlike cavity called the caeca. The ability to store food in the caeca enables spiders to go for long periods of time, over a year in some cases, without eating.
The central nervous system of a spider is in the cephalothorax. It includes the brain, which is connected to a large group of nerve cells called the gandlion. Nerve fibers from the brain and gandlion run throughout a spider's body. The nerve fibers carry information to the brain from sense organs on the head, legs, and other parts of the body. The brain can also send signals through the nerve fibers to control the activities of the body.
Spiders that bite!
Just to clear up the vocabulary. A plant or animal is considered poisonous if when ingested it causes an adverse reaction. An animal is considered venomous if it can inject a poison into another animal. Plants are not classified as venomous, although you could say that plants like stinging nettles and poison ivy, which produce toxins, could be classified as such.
Spiders known to cause problems (U.S.A.)
There are two spiders in particular of which homeowners should be wary. They are the black widow and the brown recluse. The homeowner should not handle either spider. They are easily recognized, even from a distance.
The black widow is most easily recognized by the hourglass marking on the underside of its abdomen. When bitten, a neurotoxin is released that can cause dull pain and cramping in muscles, that can be accompanied by sweating and vomiting. Less than 1% of black widow bites result in death.
First aid for someone who has been venomized by a black widow can include the following:
Use an ice pack or alcohol to reduce the swelling in the area where the bite is located.
Sanitize the area with hydrogen peroxide or alcohol to prevent infection.
Attempt to collect the spider for proper identification.
Seek medical attention at an emergency room.
Black widow spiders are usually not aggressive. If disturbed, they will retreat to a corner of their web. These spiders are more aggressive if they are protecting an egg sac. The natural habitat of a black widow is outdoors, under rocks, brush or piles of debris. Indoors, these spiders can usually be found behind furniture, in storage boxes, etc.
Control of the black widow includes doing a thorough inspection of the premises to determine breeding areas inside buildings. When spiders are found, they can be vacuumed up easily. The bag should be disposed of outside. Webs should be removed so that potential spider activity can be monitored in future inspections. Outdoors, breeding habitats should be removed (e.g., piles of debris discarded). Pesticides labeled for spider control are warranted for serious black widow infestations. Spot treating corners in a house with a labeled pesticide, and dusting crawl spaces are some techniques available. Enlisting the services of a professional pest control operator is an option to be seriously considered for black widow infestations.
Brown recluse spiders are tan to yellowish brown with a "fiddle" marking on the cephalothorax. These spiders have a body that is about 5/8 inch long. Most spiders have eight eyes, but the brown recluse has six eyes arranged in a distinctive pattern. This eye pattern is the most helpful in identification, more than the violin or fiddle shape on the cephalothorax.
Brown recluse bites are different from black widow bites. Recall that black widow bites are neurotoxins that affect the nervous system. Brown recluse bites are cytotoxins that cause tissue death or necrosis of the bite area. Often the bite itself is unnoticed. Thirty minutes or an hour after the bite, the person will feel a burning sensation. Within eight hours, a pustule will develop. This infected area can enlarge to the size of a silver dollar. It will become ulcerated and sunken. In rare instances, the reaction could become systemic after 12 hours. A systemic reaction is characterized by fever, nausea, and vomiting. Children are most prone to systemic reactions.
First aid is generally the same as with black widow bites:
The person who was bitten should be taken to a medical care facility as soon as possible.
If the spider can be found, it should be collected and taken with the patient to the doctor.
Doctors may prescribe corticosteroids, such as prednizone, along with antibiotics to prevent bacterial infections in the lesion.
Lesions may take months to heal.
Control of the brown recluse spider is critical. The services of a professional pest control service should be enlisted if a severe infestation is in the house because of the medical importance of this spider. Until the brown recluse is completely controlled in a home, occupants should carefully check their beds before going to sleep. Bites are often inflicted when someone rolls onto a spider during sleep. A favorite hiding place is the folds of sheets. Bed skirts should also be removed so these spiders cannot use them to crawl onto the bed.
The brown recluse normally live outdoors under rocks, logs and other like debris. These habitats should be eliminated. Thorough inspections are critical to the successful control of this spider indoors. The inspection can include the use of stickyboards for monitoring purposes. These traps should be placed along the walls. Flushing agents and a flashlight are useful inspection tools.
During the inspection, rubber bands should be placed at the bottom of pant legs to prevent spiders from crawling up. A service technician may even consider wearing a bee veil in severely infested homes to prevent spiders from dropping down from above into shirts.
As with the black widow spider, the brown recluse is often found in storage areas (e.g., boxes). When discovered, these spiders should be removed by vacuuming them up and discarding them promptly outside. Chemical applications may be required to control and prevent future infestations. These chemicals should be used according to the label.
Most spiders are beneficial and should be left alone. The black widow and brown recluse however, have serious medical consequences and warrant professional pest control services.
(NW US, Utah) This is often seen as an aggressive house spider. The bite does not especially hurt - feels like a pin-prick (which is what one would expect from the physical action of the fangs). Many people get nasty necrotic lesions because of the bite, since they figure, "oh, didn't hurt, it doesn't matter", or they are bitten in bed, and never feel the bite. By the time the wound necroses, it is too late to treat!
Occasionally found on bananas from South America in U.S. grocery stores. Not known to be native, but is dangerous. Also referred to as the Brazilian wandering spider. Guiness Book of World Records has this spider listed as the most "poisonous" (should be venomous) spider in the world.
Other spiders to avoid...
Sydney Funnel Web
(Australia) The most dangerous spider in the world. They are quite common - and can survive underwater in swimming pools for several days! Supposedly quite aggressive, attacking people (and other animals, too), especially during its mating season.
(Australia) Closely related to the black widow (the red mark is on the back) and a similarly dangerous New Zealand spider.
White-tailed spider -
(Australia) The venom in its bite causes
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