Spiders

Kruger National Park | April 2017

Summer has now come to a close and autumn has arrived! The last rains of the season have probably fallen now and the temperatures are starting to drop again. With the lower temperatures and shorter daylight hours many of the insects and “goggas” start disappearing. We do not generally see a lot of invertebrates and arthropods during our winter months. As a result of the reduced presence of bugs we also see fewer spiders. This is not a bad thing as many people have a serious, irrational fear of these misunderstood creatures. The fear of spiders is known as “arachnophobia”. This is one of the more common phobias that may affect people (it is estimated that 50% of women and 10% of men show signs of arachnophobia). Other common phobias include the fear of heights (acrophobia), the fear of the dark (nyctophobia), the fear of enclosed spaces (claustrophobia), the fear of open spaces (agoraphobia), the fear of snakes (ophidiophobia), and recently one the more common phobias, ‘nomophobia’ – the fear of being without your mobile phone. Another amusing one is “hippopotomonstrosesquippedaliophobia” – the fear of long words.

The fear of spiders is generally, however, an irrational fear (there have been no known deaths from spider bites in South Africa in the past 60 years) and is most likely fuelled by the fact that people are afraid of the unknown and because spiders are so foreign-looking. The majority of spider-bites reported to hospitals are not even spider-related at all (many supposed spider bites are in fact in-grown hairs or infection from other small wounds).

In South Africa it is estimated that there are just over 2000 species (from approximately 70 families) of spiders. All these families, except those from the Uloboridae family (the feather-legged spiders or hackled orb-weavers), possess venom glands. However, in the whole of South Africa there are only six known groups/species of spiders that are thought to be considered of medical importance and can therefore be said to be harmful to humans.

These six are:

  • black widow / black button spider
  • brown widow / geometric button spider / rhodesian button spider
  • the violin spider
  • the long-legged sac spider (there is a big debate at the moment among southern African spider enthusiasts / specialists as to whether the long-legged sac spider is in fact dangerous at all)
  • the six-eyed sand spider / the six-eyed crab spider
  • Lightfoot’s lesser baboon spider / cape baboon spider
  • (Out of these species / groups only the violin spider is common in the Lebombo area. This spider is very shy and is usually only seen if one picks up rocks and logs. They generally do not go into buildings and very few people even notice that they are around).

The button spiders, the widow spiders and baboon spiders have a neurotoxic venom (affects the nervous system). The main symptoms of a neurotoxic spider bite include sharp burning pain at the site (the pain may spread to lymph nodes within 15 minutes), severe muscle pain and cramps, tightness of the chest, difficulty with walking, anxiety, sweating, fever, slurred speech, nausea and headaches.
The sac spider, the violin spider and the six-eyed sand spider all have a cytotoxic venom. Cytotoxic venom effects the cells and the tissue surrounding the bite. These may lead to a lesion forming and a wound of up to 10 cm developing. The symptoms develop gradually and often the person is unaware that he has been bitten until the area around the bite becomes painful.

Some interesting general facts about spiders:
Spiders fall under the Order Araneae and are arthropods that have eight legs, two body parts (the cephalothorax and the abdomen), breathe by means of book lungs and usually have spinnerets with which they produce silk. They are the largest order of arachnids and rank seventh in total species diversity among all other orders of organisms.

Spiders are found on every continent except Antarctica.

Although most spiders live for at most two years, tarantulas and other mygalomorph spiders can live up to 25 years in captivity.

Spiders are vital to a healthy ecosystem. They eat harmful insects (spiders eat more insects than birds and bats combined), pollinate plants, and recycle dead animal and plants back into the earth. They are also a valuable food source for many small mammals, birds and fish.

The biggest spider in the world is the goliath spider (Theraphosa blondi), which can get up to 28 cm wide.

The smallest spider in the world is the Samoan moss spider (Patu marplesi)– This spider has a body length of only 0.3 mm.

The most venomous spider in the world is the Brazilian Wandering Spider / Brazilian Banana Spider (Phoneutria sp.). Just a small amount of venom is enough to kill a human. The name “Phoneutria” comes Greek word meaning murderess. The neurotoxic venom from this spider may cause loss of muscle control and breathing problems, resulting in paralysis and eventual death by asphyxiation. Another effect of this venom on human males is priapism. The venom boosts nitric oxide, a chemical that increases blood flow. Several studies have looked at incorporating the venom into drugs for erectile dysfunction.

The majority of spiders are carnivorous, although a particular small jumping spider from Central America (Bagheera kiplingi) is notable for its peculiar diet (it feeds mainly on protein-rich parts of Vachellia/Acacia trees). No other known spider has such a thoroughly herbivorous diet.

Spiders are divided into two suborders, Mesothelae (the only living members of this suborder are from the family Liphistiidae and are found in Southeast Asia) and Opisthothelae (which can then be divided into the Mygalomorphs and the Araneomorphs). Areaneomorphs are often referred to as web-building spiders, usually have only 1 pair of book lungs and have a diaxial biting action (the fangs move sideways and inwards). Mygalomorphs, in contrast, usually do not build substantial webs (most are free-running and often live in holes or under rocks), have 2 pairs of book lungs and have a paraxial biting action (the fangs move forwards and downwards).

The silk in a spider’s web is supposedly five times stronger than a strand of steel (of the same thickness). Scientists are investigating the potential of artificially producing spider silk in order to use it to produce amongst other things bullet-proof vests and artificial tendons. Up to now scientists have been unable to replicate the strength and elasticity of a spider’s silk.
Spiders have blue blood. In humans, oxygen is bound to haemoglobin, a molecule that contains iron and gives blood its red colour. In spiders, oxygen is bound to haemocyanin (which contains copper rather than iron).

The name “Widow Spiders” comes from the behaviour of certain spiders where the female spider may eat her mate after or during mating. Spiders, therefore, often use elaborate courtship rituals to prevent the larger females from eating the smaller males before fertilization. In web-weaving species, precise patterns of vibrations in the web are a major part of the rituals, while patterns of touches on the female’s body are important in many spiders that hunt actively, and may “hypnotize” the female. Some jumping spiders gesticulate and dance in front of the females in order for them to be recognized as mates and not food. Some male spiders will even give the females gifts of insects to keep them occupied while the male takes advantage while she is busy feeding.

Male spiders weave a small “sperm” web. They then place a drop of semen on the web, suck it up with their pedipalps, and then use the pedipalp to insert the sperm into the female. The shape of a male’s pedipalp is specific to that species and therefore acts as a “lock and key mechanism” (so that other species cannot mate with the female).

Young spiders often disperse from the hatching site by releasing one or more silk threads into the wind. The wind then catches the thread and lifts the spiderling into the air and carries it away. This is known as “ballooning”. Ballooning can carry spiders up to hundreds of kilometres from their original point. Atmospheric data-collecting balloons (sent up by scientists and meteorologists) have collected samples of spiders ballooning at a height of over 5 km above the Earth.

Jumping spiders can leap up to 40 times their own body length. If humans could jump this far, they would be able to jump over 70 meters. They jump by contracting muscles in their abdomen, which forces liquid into their back legs (in a similar way to the way that hydraulics works). The back legs then straighten, which catapults the spider forward.

There are various species of Spider-hunting Wasps or Masonry Wasps that actively hunt down spiders. Once they find a spider they then sting it, which causes the spider to become paralysed. The wasp then bites off the spider’s legs and transports it to the wasp nest or a hole in the ground, where it lays its eggs on the still-living spider. The young wasps then devour the unfortunate spider upon hatching.

And one last spider story, based on ancient Greek mythology (taken from Encyclopaedia Mythica and written by Melissa Lee)…
“Arachne was a young woman from Lydia, sometimes said to be a princess, who offended Athena, and suffered the consequences. Her story helped serve as a warning to all to take care to not offend the gods.

Arachne was gifted in the art of weaving. Not only were her finished products beautiful to look at, but the very act of her weaving was a sight to behold. Nymphs were said to abandon their frolicking to come observe Arachne practice her magic. So remarkable were her works that observers often commented that she must have been trained by the very patron goddess of weaving, Athena herself. Arachne scoffed at this. She was disgusted at being placed in an inferior place to the goddess and proclaimed that Athena herself could not do better than her.

Athena was quite perturbed at Arachne’s bold claim, but she decided to give the young woman a chance to redeem herself. She came to Arachne disguised as an old woman and warned her to be careful not to
offend the gods, lest she incur their wrath. But Arachne told the old woman to save her breath. She welcomed a contest with Athena, and, if she lost, would suffer whatever punishment the goddess deemed necessary.

The goddess accepted the challenge and revealed her true form. The nymphs who had come to watch Arachne’s weaving shrunk back in fear, but Arachne stood her shaky ground. She had made a claim, and she was sticking to it. So the contest began, the mortal at her loom, the goddess at hers. Athena began to weave the scene of her contest with Poseidon for the city of Athens. A beautiful scene developed from the threads, showing Poseidon and the salt water spring, and Athena with an olive tree, gifts to the people who would name Athena as their patron, and their city after her. The bystanders marvelled at the goddess’ work.

Arachne, for her part, created a tapestry showcasing scenes of Zeus’ various infidelities: Leda with the Swan, Europa with the bull, Dana and the golden rain shower. So exquisite was the mortal’s work that the bull seemed lifelike, swimming across the tapestry with a real girl on his shoulders. Even Athena herself was forced to admit that Arachne’s work was flawless. (Whether or not Arachne was actually better than Athena is still a mystery.)

Angered at Arachne’s challenge, as well as the presumptuousness of her choice of subjects, Athena tore the tapestry to pieces and destroyed the loom. Then she touched Arachne’s forehead, making sure that she felt full guilt for her actions. Arachne was ashamed, but the guilt was far too deep for her poor, mortal mind. Depressed, she hanged herself.

Athena took pity on Arachne. She most likely did not expect that Arachne would commit suicide. She brought her back to life, but not as a human. By sprinkling her with the juices of aconite, Athena transformed the woman into a spider, her and her descendants to forever hang from threads and to be great weavers”.

Images are of the following spider species: Banded-legged Golden Orb-web Spider (main image), Wall crab spider, Horned baboon spider (photo by Tams Bissett), Garden orb-web spider, Tropical tent spider web, Banded legged golden orb-web spider, Violin spider, Fishing Spider, Slender crab spider, and the Orb web.