Spinders

Southern Africa is home to over 64 families of spiders, representing more than 3,800
different species. These amazing creatures can be found in every kind of terrestrial habitat.
They spin intricate webs, mimic other animals and feed off a variety of prey. They are one
of the most successful predatory groups of arthropods on earth.
All spiders, except a single family, have a pair of venom glands that secrete venom.
Worldwide there are about 34,000 species of spider with only 20 or 30 species being
dangerously venomous to humans. Spiders do not target humans as prey but instead use
their venom as a defence mechanism. The primary function of venom is to immobilize
prey. As a secondary function, venom is used in defence against would-be predators.
It's well known that spiders have silk glands and spinnerets. They use these apparatus
not only to spin a web to catch prey but also to strengthen burrow walls, wrap up prey
remains, construct egg sacs, and build shelters. They are even used during courtship.
Spider silk does not consist of a single thread but is similar to a rope in structure with
many fibres making up the strand of silk.The strength and elasticity of a spider web depends
on the amount of water in the silk. Dry silk is stiff and snaps if stretched beyond 30% of its
original length. Wet silk is highly elastic and may stretch to 300% before breaking. Many
spiders use dry silk to construct the support lines in their webs and wet silk to provide the
sticky capture nets. In many cases spiders will eat their web in order to recycle the energy
used up to spin the web in the first place.
Large spiders may have unwanted guests in their webs. In many cases kleptoparasites
may be found in the webs of other spiders. These kleptoparasites do not spin their own web
nor do they capture their own prey. They simply inhabit the webs of other spiders and feed
on whatever the host has caught.
Spiders are preyed upon by various animals. Some spiders specialize in preying on their
fellow spiders. They have many physical and behavioural ways in which to evade predators.
Some species are camouflaged, not only to sneak up on prey but also to evade detection
from predators. Others break up their outline as they wait in the centre of their webs by
a very un-spider-like appearance, or by placing debris in the web, or construction of a
stabilimentum, which is often a zigzagging reinforcement in the centre of the web.
Some wasps parasitize spiders. They paralyze a spider and then place the spider in a
burrow or chamber. The wasp lays an egg on the paralyzed spider and when the wasp egg
hatches, the spider is eaten alive by the wasp larvae.
Spiders are adapted to their predatory lifestyles in some spectacular ways. They can go
without food for long periods of time. This enables them to maintain their normal activity
patterns in environments that have little prey. Many species live in specific habitats in
order to take advantage of specific prey found within that habitat. Hunting strategies
include sit-and-wait ambush tactics and deception. Their prey consists of many different
animals. Ground-dwelling species for example, feed on crawling insects and their larvae,
while spiders that construct webs often target flying prey such as locusts, flies and moths.
All stages of insects are preyed upon including the adult stage, larval stages and even the
eggs. Some spiders specialize in catching vertebrates such as small fish and tadpoles. Some
desert spiders are known to prey upon geckos.
Spiders display amazingly varied behavioural characteristics. These behaviours are
linked to their hunting strategies, courtship or social structure. Some jumping spiders
for instance mimic ants. These ant-like spiders not only look and behave like ants but-also
smell like ants. Other forms of mimicry include bird droppings, ladybirds, twigs and bark.
Some spiders even mimic other spiders in order to lure them out of their web and prey
upon them.
Many species of spiders display complex courtship rituals where the male entices the
female to mate. Courtship can include tactile behaviour such as plucking or strumming
the female's web, or may include waving of pedipalps in order to seduce the male's suitor.
Males are often very cautious during courtship. In many cases the female is substantially
larger than the male. Males often get eaten by the female but after millions of years of
evolution, many males have developed ingenious ways to avoid becoming a post-mating
snack.
Courtship among spiders can be an intricate and delicate affair. In many species,
a male will approach the female. and signal his intentions. Once the female has proved
receptive the male will approafhthe female and mate. In other species courtship is far
more complex.
Spiders represent a major influence in terrestrial habitats. Their success can be attributed
to their resilience to tough environments and their ability to exploit ecological niches that
no other creature occupies.
Many kinds of web-building spiders are distributed over large ranges while spiders that
burrow in the ground show definite preferences to specific substrate. Many spiders can be
simply identified by using their web, others can be identified by where they are found and
their behaviour. This text will allow you to identify the more common spiders that occur
in southern Africa. For the purposes of simplicity this chapter is limited to prominent and
common spiders that are easy to identify in the field. In this text the length of a spider is
taken from the f'Com of the carapace to-the end of the abdomen.