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Introduction to spiders

Spiders are small land-based predators with 8 jointed legs, external skeletons, two main body parts, simple eyes, no wings or antennae. They lay eggs but do not metamorphose. All spiders produce silk and many build beautiful webs.

They are probably the most abundant land-based predators and although insects are the primary prey, some can catch small birds, mammals, reptiles, amphibians and even fish. They are important biological control agents and because they occur in huge numbers they are really effective. You could call them natural insecticides!

Southern Africa with its varied topography, vegetation types and habitats from deserts to forests, mountains to wide grassy plains, man-altered landscapes and wilderness areas – has a huge number and diversity of these little predators. They range in size from the comparatively gigantic baboon spiders or African Tarantulas to adult spiders with body length of less than a millimetre. The majority are modest-sized, inoffensive and keep to themselves. There’s at least one and probably more not very far from you now. Don’t run away – they’re not out to get you! Spiders don’t eat people!

Something that is often a problem when trying to explain or identify spiders is their size. They range from really tiny, almost microscopic animals to comparative giants with body length of more than 30 mm. We measure spiders from the front of the head to the end of the abdomen.

Silk production

Their ability to produce silk has enabled spiders to colonise almost every terrestrial and some aquatic habitats. Silk has enabled them to modify the world for their own use and comfort. All spiders produce silk even those that don’t weave webs. It is used in a great variety of ways – to make homes (retreats), hiding places, line burrows, make trapdoors, safety nets,construct egg sacs and nursery webs, to spin drag-lines, safety lines, mating threads, “parachutes” and diving bells. It is a means of communication, both vibratory and olfactory and is often their first means of both offence and defence, more important to their predatory lifestyle than venom.

Venom

Most spiders produce venom which is a mixture of saliva, venom and digestive fluids, used to subdue, kill and digest their prey – usually invertebrates. In general it has little effect on large mammals including people. A bite may hurt at first, can itch for several days but if left to subside without being scratched will disappear with no lasting ill effects. Venom does not persist in the body and the effects of a bite will not recur later. Spiders will only bite if squashed against our skin – they don’t even bite in self-defence as some larger creatures do. They do not eat people. They do not make a living from sucking our blood and are not vectors of any human diseases. They cannot lay eggs under our skin and won’t make nests in our hair. In fact they will avoid contact with big, dangerous creatures like us. This means that spider bites are really rare and the effect venom of most spiders on humans is unknown because they simply don’t and often cannot bite us.

Most supposed spider bites turn out to be lesions from bacterial infections or less often to be tick, flea, mosquito or other arthropod bites. Fungal infections or lesions resulting from some underlying medical condition are also sometimes blamed on spiders. People with impaired immune systems are more susceptible to infections and such infections often cannot be diagnosed so medical practitioners take the cautious route of prescribing broad spectrum antibiotics. These work for most bacterial infections with the exception of the difficult to treat deep seated bacterial infections such as MRSA (methicillin-resistant Staphylococcus aureus). Of course antibiotics do not work on fungal or viral infections and need to be treated differently.

Author – Astri Leroy

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