Spiders should be called venomous not poisonous. This is because they inject a venom into the tissues of the body, the same applies to bees, wasps and snakes. Something that contains poisons that enter through your digestive system, or undamaged skin and makes you ill is poisonous, many fungi and the berries of numerous plants are poisonous. The Black Widow Spider is both venomous and poisonous, at least to camels.
Nearly all spiders (the family Uloboridae is the exception) produce some venom, however very few are actually able to bite a human because of the thickness of our skin. Further more of the nearly 40,000 species of spiders known to science, only about 30 are dangerous to humans. The images we hold in our mind of spiders as dangerous monsters is mostly untrue. For instance, despite what the majority people think, most species of tarantulas are timid and have only small poison glands. Getting bitten by a tarantula in the wild is quite difficult and there are no scientifically proven cases of death from tarantula bite.
Spiders produce their venoms to immobilise their prey so that they can feed without being hurt. Most spider venoms are far more effective against the invertebrates they feed on than they are against humans and other large animals. Even among the vertebrates some a re more vulnerable to spider toxins than others. For instance cows, horses and sheep are more sensitive to the venom of the Black Widow (Latrodectus mactans) than humans and many deaths of such animals from this spider's bite have been recorded. A different example is the Australian Funnel-web spider (Atrax robustus) whose venom is highly toxic to primates (12 human deaths pre 1980) but which has little effect on cats, dogs and rabbits.
Spider venoms can be divided into two different sorts Neurotoxic venoms that attack the nervous system, and Cytotoxic or Necrotic venoms that cause tissue damage. The venom of a particular spider may be a mixture of both types of toxins, but species normally specialise in one form or another.proteolytic enzymes and various amines and amino acids. Different species have different balances of substances and different toxins. Neurotoxins generally attack the synapses or the presynaptic receptors of the CNS, a-latrotoxin for instance over stimulates the body's acetylcholine and noradrenalin transmitters effectively paralysing both the sympathetic and parasympathetic nervous systems. Cytotoxic or Necrotic venoms contain proteolytic enzymes and other high molecular weight proteins that attack body tissues, causing sores, blisters and internal damage. Generally speaking neurotoxic venoms are more dangerous than cytotoxic venoms. Most snake and scorpion venoms are neurotoxic. However Cytotoxic venoms can kill, Recluse spiders produce Cytotoxic venoms.
Black Widow = Neurotoxic (Latrodectus mactans) = Bite painless = Toxin is called a-latrotoxin and it has a molecular weight of about 130,000 daltons. Pain begins 10 to 60 minutes after bite in lymph nodes. Then it spreads to muscles, muscular cramps follow, especially abdominal muscles. Contorted facial expression, swollen eyelids, inflamed lips, jaw clenched. If diaphragm and intercostal muscles affected death can follow. All this accompanied by severe anxiety. Without treatment symptoms last for up to five days and complete recovery can take weeks. Antidote and calcium gluconate will relieve symptoms in 10 to 20 minutes.
Recluse spiders = Cytotoxic (Loxosceles reclusa L. laeta, L. gaucho and L. rufescens) = Bite mildly painful = A burning stinging sensation, local swelling, and necrosis (often deep) of the skin from the enzyme sphingomyelinase, followed by restlessness and vomiting. The venom also includes haemolytic agents that turn the victims urine black and that can result in kidney failure and death. Finally it should be remembered when listening to people's spider stories that many injuries that are attributed to Loxosceles are not in fact the result of its bite. Proven mistakes include; other spiders, Chiracanthium and Steatoda, kissing bugs, pajarello ticks, poison ivy, bed sores and even allergic reactions.
Wandering Spiders = (Phoneutria spp.) = Bite extremely painful, can cause shock = sweating, accelerated heart rate, and feeling cold and tense. Bites to humans normally only involve a small amount of toxin and are seldomly fatal.
Australian Funnel-web = Neurotoxic (Atrax robustus) = Bite painful = severe pain, shivering, muscle cramps, loss of eyesight and eventually paralysis of the breathing centre which can lead to death.
Australian Redback Neurotoxic (Latrodectus hasselti), similar to Black Widow but less intense, it has caused fatalities but not since the antivenom was developed.
Man is an ingenious animal, and both the natives or North America and the Bushmen of the Kalahari (Africa), used spider venoms on their arrow heads. In the modern world scientists are looking into using spider venoms as insecticides.
|Spider Silk||Spider Anatomy||Bibliography and Reviews|
|The Fear of Spiders||Reproductive Ecology||Spiders and Man|
|Ecological Considerations||Tarantula Myths||Spiders and Evolution|
|Caring for your Tarantula||A House-spider Safari||Fear of Spiders|