8 Unusual Facts About Spiders
How Many Eyes Do Spiders Have?
It depends on the spider! Some have up to 4 pairs of eyes, others have only 3 or 2 pairs. They are not compound eyes, like insects have and usually only one can form good images. The other eyes are only capable of detecting the direction from which the light is coming.
In the minds of most people spiders are dumped in the same set as other creepy crawlies, but they are not insects. They belong to the family of arachnids and are related to mites, scorpions and ticks
Spiders can be easily distinguished from insects because they have eight legs rather than six.
Spiders are the most numerous group of arachnids with 40,000 different species identified.
Spiders Digest Their Food Before Eating
Spiders cannot eat solid food. Instead they inject, or cover their prey with digestive enzymes, and wait for it to turn into a nutrient broth and then suck it up using their pharynx.
Once inside their stomachs the broth is digested further and nutrients are absorbed.
Most Spiders are Venomous
The vast majority of spiders produce neurotoxic venom with which they paralyse their prey. They have a pair of fangs, known as chelicerae, which are connected to a toxin gland. When the fangs stab their prey, they act as needles, injecting it with venom.
Most spider bites are no more dangerous to humans than a bee sting. In fact most spiders are too small, and their fangs too short to penetrate human skin. Of the 40,000 species, only about 200 have bites that are venomous to humans. In the US the most dangerous spiders are the black widow and the brown recluse spider.
Both species are actually very shy and they would much rather hide from humans than attack them. Unfortunately their hiding places can sometimes include places where a human will disturb them and they will bite in self defence.
Overall there are about 100 recorded deaths from spider bites in the last century. When you think of all the people who have died from other causes, this really represents a very small number.
The black widow spider venom is neurotoxic. It results in the release of excessive acetylcholine, norepinephrine and GABA neurotransmitters which prevent muscle relaxation. The venom initially causes severe pain around the bite area, but rapidly enters the circulatory system and affects muscles around the body, causing severe cramps. Complications can include severe kidney failure, heart problems or paralysis, but they are rare.
In contrast the bite of the brown recluse spider generally doesn't hurt. However the venom contains tissue destroying toxins, which lead to necrotic lesions, which leave scars even if they heal. There is no definitive treatment for the bites. It is thought that many lesions that are attributed to the bite of this spider, are in fact caused by other factors.
It is hard to definitely identify the most venomous spider. In 2010 the Guinness Book of Records bestowed that doubtful honour on the Brazylian wnadering spider found throughout South America. Its venom is definitely potentially deadly, it works by blocking calcium channels, leading to paralysis and possible asphyxiation.
However there is an effective antivenom against the spider, and experts believe that it often delivers dry bites, in which it doesn't inject venom, or only injects a small amount of venom. However, bites in which the spider injects a full does of its toxin are certainly very dangerous.
All Spiders Produce Silk
All spiders have spinnerets on their abdomen (tummy) which produce silk. Each spinneret has numerous spigots, each of which is connected to a silk gland.
Spider silk is made mainly of protein. It has a similar tensile strength to nylon but is much more elastic so can be stretched very far before breaking. The silk is first liquid but then solidifies as it is stretched.
A spider can produce different types of silk, which have different functions. Some threads can be covered with glue droplets which helps trap insect prey.
The most familiar use for spider silk is the big orb-shaped webs that they use to catch their prey. However only some spiders are orb weavers. Other spiders construct funnel webs, or horizontal sheets with a few upwards-extending threads. An insect is caught by the thread, and shaken into the web below where it becomes entrapped.
Only some spiders use their silk to trap prey. Others like the trapdoor spider and tarantulas are ambush predators.
Spiders use their silk for many other purposes, including building shelter, encasing prey to immobilise it, protecting their egg capsules, and building parachutes and aqualungs.
Yes, you read the last two points correctly. Spiderlings (baby spiders) move around using threads of their silk as parachutes. They produce a few very fine threads, called gossamer, which get blown by the wind, taking the baby spider with them.
How Jumping Spiders Catch Their Prey
Diving Bell Spiders Live Underwater
Diving bell spiders, Argyroneta aquatica, are the only species that spend their whole lives underwater. Like all other spiders, they still need to breathe atmospheric air. They get around this problem by having an air bubble, which is held to their bodies by the fine hairs that cover them.
The female, also builds a bell shaped dome, out of spider silk, which is filled with air. She spends most of her life in her dome, only venturing outside to catch prey. She also lays her her eggs in it, and sits there to digest her food.
Cobwebs Were Used in Traditional Medicine
Cobwebs, which form in the corners of any room, trapping dust and looking messy. However, in past centuries they were considered frequently used as dressings for wounds, because they were believed to stop bleeding.
I remember reading historical novels of valiant warriors in the 16th and 17th century, who would frequently sustain wounds in battle. Whenever they were hurt, there was always a call for cobwebs, which would be kneaded with bread and placed on the wounds.
So is there any truth in the ancient belief that cobwebs help? They are particularly rich in vitamin K, essential for blood clotting. So it is possible that they stopped brave heroes from bleeding to death. An important consideration in the days before blood transfusions.
Spiders Have Taken Part in Space Experiments
Yes, spiders have been astronauts. In 1973 experiments were conducted on how low gravity affects the structure of spider webs. Two European garden spiders, Anita and Arabella, were taken aboard skylab 3 and told to do their stuff.
The first attempt at spinning a web by Arabella was very unsuccessful. However later on she appeared to get her bearings and managed a much better web. It was still irregular compared to the orbs produced by these spiders under normal conditions. It appears that spiders require gravity to orient them when they are making their webs.
Some Female Spiders Eat the Males After Mating, But Most Don't
Cannibalism is which the female eats her partner after mating is not actually all that common. Most males survive several matings and die of causes other than being eaten by the female.
Males are usually much smaller than females. To ensure that they are not mistaken for just a potential food item, when they first approach their bride, most spiders engage in complicated mating rituals. These might include signalling through special vibrations through her web, so the female knows that a male is approaching.
However is some species it is usual for the female to consume the male after a successful mating. This habit has given the black widow its name. The males don't appear to do much to defend themselves. It is thought that the extra nutrition can help the female produce healthy eggs and offspring, so the male is sacrificing himself for the sake of his offspring, so to speak.