Spiders - The University of New Mexico



Spiders

Introduction

Toxins

Medical Importance

First Aid

Folklore, Misconceptions

Melissa Wilson

University of New Mexico, Biology 445

April 30, 2008

Introduction

There are roughly 34,000 known species of spiders, 2000 of which may be found in the United States. It is expected, however, that there are as many as 200,000 species in the world and that arthropods in general compose about 75% of the world’s animal species. Nearly all of them use some sort of venom to subdue their prey. These venoms are mixtures of individual toxins that may include enzymes, nucleic acids, amino acids, inorganic salts, monoamines, proteinaceous and nonproteinaceous toxins.

Spider Milk…

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Research on spider toxins is seriously limited by the extremely small quantities that may be obtained. Milking a spider that is only a few millimeters in diameter clearly presents some difficulties. This is why most of the information on spider venom is limited to the large and those known to be dangerous.

Toxins

There are many components that make up each spider venom. The three main kinds are polyamines, polypeptides and large proteins.

Polyamines

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The aromatic region of the molecule is hydrophobic, while the tail is hydrophilic.

Polyamines block ion channels or receptors. The receptors that are targeted respond to amino acids, specifically N-methyl-D-aspartate (NMDA), quisqualate (QA), or kainate (KA). The toxins, therefore, are antagonists of these amino acids.

Some examples include AGI and AGII which are calcium antagonists found in Agelenopsis aperta venom. Joro spider toxin (JSTX) blocks postsynaptic glutamate receptors and is produced by Nephila clavata. Argiope lobata venom contains a similar toxin called argiopine, or argiotoxin, which also blocks glutamate receptors.

Polypeptides

The mass of the peptides is from about 3000 to 10000. These are the most effective parts of most spider toxins. They work by blocking the ion channels involved in neuronal communication: calcium, sodium, and potassium. The majority of these peptides have the same structure and fold to form a beta sheet.

This group is broken into three groups: alpha-toxins, mu-toxins, and omega-toxins. The alpha-toxins block the acetylcholine receptor on the postsynaptic cell which inhibits propagation of action potentials to communicate with muscles particularly. The mu-toxins are more direct in ending muscular action potentials by blocking sodium ion channels. Finally, omega-toxins keep calcium from being released to activate the SNARE complex, thus preventing release of acetylcholine.

Proteins

Proteins are anything with mass over 10000. The best example of a protein toxin is alpha-latrotoxin from the black widow spider. It causes excessive release of the calcium ions so that acetylcholine floods the synaptic gap. This results in hyperactivation of the postsynaptic cell. Enzymes are also commonly used, and sphingomyelinase D is a component of brown recluse venom, causing the cellular degradation.

Medical Importance … and other uses

This is a short list of the many uses that have been found for some of the toxins in spider venoms.

Tarantula Venom

Toxins found in tarantula venom have been found to be useful in treating strokes, heart attacks, and brain tumors.

There is a particular peptide that blocks ion channels involved in cellular responses to environment. This can make heart attacks and the growth of brain tumors slow down. The reason for this is that a heart attack causes the heart cells to stretch, opening the ion channels. Brain tumors actually cause release of growth factors from surrounding cells probably due to stretching. The peptide keeps the swelling down so that the ion channels do not open so much.

Strokes occur when there is a blockage of oxygen to the brain. This typically results in brain damage of the affected areas because of lactic acid accumulation. When oxygen is not available, the brain begins anaerobic glycolysis to obtain energy, resulting in lactic acid waste. Acidic conditions induce elevated release of calcium in the neurons, which is highly toxic to the cells. A toxin found in the tarantula spider actually blocks acid-sensing ion channels, limiting brain damage.

Male impotence

The wandering spider (Phoneutria nigriventer), which is actually a very dangerous species, may be useful in treating male impotence. The specific toxin is called Tx2-6 and is still being investigated at the Medical College of Georgia as of April 2008. Apparently, men who have been bitten reported long lasting, painful erections; then an improvement in their sex lives. The researchers are working on a method that may combine preexisting erectile dysfunction medications with the toxin to enhance their effects.

Insecticides

Spider venoms are specifically geared towards killing insects, which makes them rather perfect insecticides. The funnel web spider venom is what has been most studied for its use in this area. There are around 200 compounds in the venom, some of which are potentially fatal to humans. Most of them, however, kill insects without having any adverse effects on humans or other mammals. These insecticides could be genetically engineered to target specific pests, as well, by using a virus rather than just spraying the insecticide. Development of immunity would not be such an issue either. Not only would this method be more effective in controlling insect pests, but it is also far safer and more environmentally friendly. The studies have shown that although small quantities are lethal to insects like cockroaches, large quantities do not harm mice at all.

First Aid

Bites are most dangerous to the very young and the elderly, as well as those who are ill or in some other way immunocompromised. There is a general procedure that should be followed until medical help is available for anyone who has been bitten.

1. Keep the person still and calm. The bite will probably not be fatal, and there is most likely an antivenin available.

2. Wash the area thoroughly with soap and water, or apply an antiseptic.

3. Bandage firmly just above the bite to slow down the spread of the venom. Do not cut off blood circulation to the area, however. ***This should not be done if the spider is known to be a redback, since it will only make the wound more painful and does not help.

4. Ice the area.

5. Try to catch the spider…

The last step may seem odd, but it will help immensely at the hospital if the doctors know what antivenin to use. Even a crushed spider may be identified, though, so don’t get bitten again just trying to catch it. It is also very important to clean the bite to prevent infection and possibly necrosis. It is not uncommon that the bacterial infection that sets in is more dangerous than the venom itself.

The most important thing to remember is to keep the person calm. Oftentimes, this is the only treatment necessary.

Folklore, Misconceptions, and other Nonsense about Spiders

Spiders are usually not aggressive animals and will not bite unless provoked. In the US, even if a person is bitten by a spider the chances of it actually being dangerous are pretty slim. A bite should never be ignored, but there is no reason for the rampant arachnophobia.

There are a lot of strange stories about spiders that really have no facts behind them. For example, the daddy longlegs spider is commonly said to have the most potent venom of any spider, but its jaws are too small to be able to pierce our skin. Basically, if no one has ever been bitten by a certain spider, it is impossible to say how dangerous that spider is. Wolf spiders are also harmless, though they are somewhat frightening to look at especially if they are running towards you. By the way, not all hairy spiders are wolf spiders. Other harmless spiders include the white-tailed spiders, sac spiders, and even the jumping spiders. Though these spiders are harmless, there is some pain and swelling usually associated with the bite for some time.

(Figures from left to right: daddy long-legs, sac, wolf, jumping, and white-tailed spiders)

One myth that has been circulating for a while has to do with the camel spider in the Middle East, also known as the sun spider. I know that most of you have heard this one. Apparently there is a common belief that the camel spider can not only run at speeds comparable to a HumV, but also injects some sort of anesthetizing compound into its victims while they sleep so that they do not feel it eating their flesh and wake with a gaping wound. I even heard that it can disembowel camels and lay its eggs inside. Actually, the camel spider is pretty creepy looking and does reach speeds of up to 10mph, but it also does not have any venom, let alone an anesthetic.

Despite their imposing appearance, the tarantula does not have a venom that is dangerous to humans. The bite may be painful, however, since they have such large jaws. The only other risk associated with tarantulas is itchy hands if you neglect to wash after handling one.

I think my favorite myth of all is that a person swallows an average of 3 to 4 spiders a year while they sleep. Where did they come up with that one? How would you even go about trying to study it?

There are dangerous spiders, but deaths caused by spider bites or even symptoms beyond pain and irritation in the US are almost unheard of.

Those spiders that may actually cause damage are the brown recluse (Loxosceles), black widow and redback (Latrodectus), funnel web, mouse (Missulena), baboon (Harpactirella lightfoot) and wandering (Phoneutria nigriventer). The redback, funnel web, and mouse spiders are found in Australia, the baboon spider is from South Africa, and the wandering spider is from South America. The only spiders that may be cause for concern in the US are the first two: the brown recluse and the black widow. Though these spiders are dangerous, there is more paranoia about them than is justifiable.

Brown Recluse (Loxosceles Reclusa)

The brown recluse bites when disturbed, and often the bite may not be felt at all. The symptoms present after about 6-8 hours and include dermal necrosis with fever, hemolysis, thrombocytopenia, and renal failure. Clearly this spider’s venom is especially toxic and they should definitely be avoided, but the occurrence of brown recluse bites is ridiculously exaggerated. Just be careful when delving into dark closets that are seldom used, or cleaning out the woodpile in the backyard.

Infection by Staphylococcus aureus produces a wound very similar to the bite of the brown recluse spider. Oftentimes, the bacterial infection is misdiagnosed as a spider bite, which seems to justify peoples’ hysteria about spiders. This spider’s habitat is limited mainly to the Midwest and the South, though that does not stop many people from claiming the source of any odd mark on their bodies to be this spider. Confirmed bites are extremely rare.

Brown recluse Staphylococcus aureus

Other conditions that may produce similar symptoms include such varieties as fungal (ringworm), bacterial (Staphylococcus, Streptococcus), or viral (herpes) infections, arthropods like ticks (Lyme disease), lymphoma, vascular disorders, even chemical burns and bad reactions to drugs like warfarin. Yet the diagnosis generally involves a spider.

 

It is not impossible to see the brown recluse in other areas than those highlighted, but this is due to the movement with people. So we seem to be pretty safe from the brown recluse here. Just watch out for herpes and ticks to avoid the nasty looking sores.

Black Widow (Latrodectus hesperus)

The black widow (Latrodectus hesperus) is by far the most recognizable of all spiders. Though its venom is highly toxic, its reputation is somewhat exaggerated.

Bites are painful most of the time, though there are those who do not feel them at all. Symptoms last from 1 to 3 days and begin within about 2 hours. They include painful symptoms such as cramps in the torso and legs, weakness, itching, nausea and vomiting, respiratory difficulty, and increased blood pressure. Headache and anxiety have also been reported.

Like the brown recluse, however, the bites of the black widow are most dangerous to the very young, the elderly, and the ill. To others, the venom is not fatal and it is not even always necessary for hospitalization.

As may be seen from the map, the Latrodectus family is literally found worldwide.

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A few last things:

1. Just because you do not know the source of a bite does not make it a spider bite.

2. Two adjacent marks are not the telltale sign for a spider bite. The chelicerae are generally too small to leave marks at all. It’s probably from an insect or other arthropod that bit twice.

3. Spiders are rarely aggressive. If you leave them alone, they will not bite you.

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