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– Game Ranging / Field Guiding Course

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Invertebrates © Copyright

Module # 2 – Component # 4

Spiders

Objectives:

To achieve an introduction to and understanding of the Order Aranae within the Class Arachnida.

Expected Outcomes:

To be able to recognise all spiders based on their external anatomy

To gain insight into their general anatomy and physiology

To become familiar with the different ecologies of spiders

Sac Spider



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Spiders (Order: Araneae) There are over 32 thousand species of spiders known world-wide. In a similar

scenario with ticks and mites (Component # 3) this number probably only represents a portion of their number, the majority remaining undiscovered. Spider

populations may be extraordinarily large. One scientific study estimated that in an undisturbed acre of grassland, meadow or forest, there may be upward of 2 million individuals. In Africa, spiders have been divided up taxonomically into two sub-

orders, viz. the Orthognatha and the Labidognatha.

Orthognathous species are usually large, primitive free-living spiders. All have four lungs and chelicerae that move in a vertical plane parallel to the long axis of the body. They therefore deliver a “stabbing” bite.

Labidognathous species are usually the web-spinning species. They have

only two lungs and their chelicerae move at right angles to the long axis of the body. They deliver a “pinching” bite.

Some survival strategies which spiders have evolved are examined here.



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Silk and Spinnerets The silk spinning apparatus of spiders is known as spinnerets. These are

independently mobile appendages at the end of the abdomen. Each spinneret is supplied with silk by a silk-producing gland located in the abdomen.

Silk is a liquid protein (glycine, alanine, serine and tyrosine) that can only be formed into a thread by stretching. This the spider does with its legs, or by

anchoring the silk and then moving off, thereby stretching it. The stretching action changes the molecular structure of the silk and allows it to harden.

Different glands produce different types of silk such as adhesive silk, stabilimenta and draglines. Silk has the approximate tensile strength of nylon of the same thickness, although it’s far more elastic.

All spiders produce a dragline as they move about. This is designed as a safety

precaution, but has reproductive uses as well. As the spider moves, it draws out a long line of non-adhesive silk that it attaches to the ground at various intervals using adhesive silk. Should the spider fall off the branch it is always able to climb

up the thread back to its original position.



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Food and Feeding All spiders are predatory. Most species feed on small creatures such as

arthropods, but others are known to take lizards, birds and fish.

Orthognatha – Free living species

Cursorial species are those that wander around in search of prey. Once they locate a suitable victim, it is chased down and killed with bites of the large stabbing chelicerae. Included in this group are the:

Wolf spiders

Lynx spiders

Fisher spiders

Crab spiders

Jumping spiders

Baboon spiders

Tarantulas

Trap door spiders

Spiders belonging to this group have evolved a variety of ‘hunting’ strategies:

Some are opportunistic roamers. They wander around simply catching insects they happen to encounter, Wolf spiders hunt in this manner.

Others prefer a sit and wait strategy. They find a suitable, hidden location and wait for suitable prey to wander past them.

Crab spiders take this method to the next level, by sitting in flower heads and

ambushing visiting insects.

Trap door spiders construct a burrow from which to ambush unsuspecting

prey. Their burrow is constructed with a silk hinged trap door, which they cover with moss and soil to camouflage it. The spider then waits just beneath the lid

and is alerted to the presence of prey either by the vibrations of their movement or a strategically placed dragline, functioning in much the same way a trip-wire does. Successful trap door spiders may remain in the same location for many

years.



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Labdiognatha – Web spinning species The construction of a spider web is truly one of the special wonders of nature. Web

spinning relies on several different factors and applications. These include:

Weight

Leg length

Silk supply

Appetite

Instinctive behaviour

Locomotor activities

However, most bizarre of all is the

fact that visual information is not necessary at all! Blinded spiders can build flawless webs. No aspects of

web construction are learnt and the most complex of web designs can

immediately be built by hatchlings. The entire web, or at least the

adhesive spirals is replaced every 24 hours, as silk loses its stickiness

every few days. The old silk is eaten, and the protein is re-assimilated back into the spider’s protein

glands. If a web is destroyed by birds or weather for example and

cannot be eaten, some species may only be able to spin a new web sometime later, when their silk

glands have had an opportunity to manufacture more protein.

Spiders with an ample amount of protein may be able to replace their entire web in a remarkably short period. In one study a spider was seen to be able to complete

an entire web in less than an hour, using more than 20 meters (66 Feet) of silk.



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How a spider web saved a man’s life

During the second Anglo-Boer war (1899) a

young British soldier found himself on the run from a group of Boer scouts. The young

man was a few hours ahead of the scouting party and in desperation decided to hide at the bottom of an abandoned well. When the

scouting party came across the well, they looked down and saw a web covering the

entire entrance to the well, with the bottom being in darkness. Seeing the web, the scouts wrongly assumed that the man they

were searching for could not have been at the bottom since a spider had long since taken up residence in the mouth of the well, and if the man had jumped into it,

there certainly could not be a spider web there. The young British soldier climbed out much later and related this tale in his diary.

Web-weaving species are sedentary (largely never moving away from a chosen point) and rely on their webs to entangle their prey. There is a great deal of

variation in web designs, the web of each species differing from the next. Webs may be made in a horizontal or vertical plane, of thick or thin silk, of adhesive or non-adhesive silk, of single strands or woolly strands. Some species’ webs have

stabilimentum – a quite visible zigzag feature at the centre of the web thought to warn birds and other animals of the presence of the web.

It is still not fully understood how spiders can cut silk with their chelicerae, and

why they do not stick to their own webs. The function of the web is to trap insects and other arthropods on its sticky

surface where the spider can deliver the coup de grace (killing action). Many spiders wrap their prey up in a silk bag and store it for later consumption. Moths

and butterflies frequently escape from webs because of the loose scales that they have on their wings. These stick to the adhesive silk, allowing the victim to fly free.

Kleptoparasites are species that live in the webs of others and steal the prey

that is too small for the owner of the web to bother about. Mercury spiders are Kleptoparasites that are frequently seen in the webs of the various orb-weaving spiders.

Most spiders live a solitary lifestyle, only seeking out others to mate. A few families

however have evolved some form of social organisation. These social spider species build and share a communal web and co-operate in the capture, killing and sharing of prey. Communal spider webs may be of significant dimensions, some

being more than 3 meters (10 Feet) across.



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Spider Venom Venom is produced in a gland at the base of the

chelicerae, and is used to subdue prey. Only a few species have venom that is dangerous to man.

A detailed discussion on spider bites – the diagnosis, treatment and management thereof can be found in

Module # 11, component # 5.

The button spiders (Latrodectus genus), the violin spiders (Loxosceles genus) and the six-eyed crab spider (Sicarius genus) are the only South African species with the potential to kill a person.

North American tarantulas, despite their

size, reputation and look are not particularly venomous. Their venom is a cytotoxin with the approximate strength of

a bee sting. Their reputation is also somewhat unfounded with Arizona guide

Steven Rich who frequently demonstrated their gentleness to clients by allowing male tarantulas to crawl all over him (Pers.

Comm → S. Rich, March 2006).

Spiders feed in the distinctive arachnid fashion. Preliminary digestion takes place outside the body. After prey has been captured and immobilised by the

chelicerae and pedipalps, digestive juices are poured from the midgut onto the open wounds caused by the mouthparts. The soft internal parts of the prey are

rapidly digested into a “soup” that is then sucked into the mouth and alimentary canal, where it is further processed.

Although not as spectacular as some of the Acari (ticks and mites), some spider species can go without food for relatively long periods. This is an adaptation to a

predatory lifestyle that inherently has an uncertain food supply. In addition to this many spider have extremely low metabolisms.

We have said before that spiders play a predatory role in any given ecosystem. This is only half true. Spiders are also the chosen prey for many species. These

include small mammals like the suricate, insectivores and other rodents. Many bird species regularly prey upon spiders as do lizards and other reptiles. In some cases, spiders find themselves as being prey specific. The Pompilid wasp actively hunts

large spiders to kill them, drag them to an underground nest and lay her eggs on them.

Therefore, when defining the role of spiders in an ecosystem, it is important to understand that like many other groups of animal, they function as both predator

and prey.



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Medically Important Spiders in South Africa By: Jonathan Leeming

Introduction Spiders have fascinated humans for thousands of years. Often a symbol of evil and fear, spiders have sparked the public imagination for all the wrong reasons. The media portrays them as deadly venomous, we’ve all received the shocking

emails, read the horror stories in newspapers, but how venomous are these creatures really?

All spiders except one family, the Feather legged spiders (Uloboridae) have a pair of venom glands that secrete venom. Worldwide there are about 34,000

species of spider with only 20 to 30 species being dangerously venomous to humans. The primary function of venom is to immobilize prey. Prey is

considered to be insects although some spiders are known to target small vertebrates. Some spiders have venom that is particularly effective against certain prey.

Spiders have a pair of venom glands which secrete venom. Muscles around the

venom gland squeeze venom out, through the venom duct and out of the spider’s fangs. Large spiders such as Baboon Spiders do not necessarily have

large venom glands. Many spiders rely on their brute strength to subdue prey until the venom takes effect. These spiders often have spines on their legs which provide extra grip on struggling prey.

Their venom is also used in defence against larger animals such as humans and

would-be predators. Statistically, spider bites are less dangerous than wasp and bee stings. Some animals such as cows, sheep and horses are more sensitive to spider venom. There have been cases of fatalities in dogs from Baboon spider

bites. Other animals are known to be more resistant.

There are many spiders that are found in houses and outbuildings. It’s only a matter of time before they come into contact with people in some form or manner. Most spiders are shy and reclusive and avoid physical contact. Only when

the spider is squeezed, touched or threatened do they defend themselves and bite. It must be noted that the majority of spiders possess fangs that are too

small to pierce through human skin. Spiders have 2 types of venom either cytotoxic or neurotoxic.

Note that the length of a spider is measured from the tip of the carapace to the end of the abdomen.

Another interesting statistic is that there have been no fatalities in South Africa due to spiders in the past 60 years.



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Venom Types Spiders have either cytotoxic or neurotoxic venom. Each kind of venom exhibits characteristic, signs and symptoms and warrants different medical treatment.

Note that spiders are venomous, not poisonous. Poison must be ingested to have

any effect. Venom needs to be injected into tissue. Theoretically, venom can be drunk without any ill effects, unless of course you have mouth or stomach cuts, sores or ulcers.

Cytotoxic Venom

Results in the death of tissue cells, causes tissue damage and

blood vessel leakage.

Bites result in tissue necrosis and often go unnoticed until a lesion develops. Bite symptoms often

develop slowly and the area becomes painful and

discoloured. The spider responsible for the bite is often difficult to identify since bites

usually happen at night. Bites are painless so the culprit is

rarely captured.

In southern Africa, two genera of cytotoxic spiders are medically important - the Sac spider (Cheiracanthium sp.), the Violin Spider (Loxosceles sp.).

Neurotoxic Venom

Affects the nervous system of the victim causing acute pain. The nervous system is affected through heart palpitations, respiratory problems, blurred vision and slurred speech. Southern African Button Spider (Latrodectus sp) possesses

neurotoxic venom of medical importance. Southern Africa is home to 6 species of Button spider. These spiders are divided into two groups based on their

appearance, the Black Button spiders and the Brown button spiders. Note

Another spider, the Six eyed sand spider is also reputed to be highly venomous.

This spider has cytotoxic venom. Although research indicates that these spiders are highly venomous there are no authenticated records of bites from this spider in southern Africa. This spider has been included due to its potential for

being medically important.



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Factors Influencing Spider Bite Symptoms Different individuals can have different reactions to spider bites. Spider

envenomations are influenced by the following factors:

Health and age of the victim. Venom will affect someone with a small body mass more than a person with a large body mass as well as the aged.

Some people are sensitive to spider venom. In these people, bite symptoms

develop at a faster rate and are more extensive. Note that there are no records of anyone being allergic to spider venom.

Amount of venom injected during the bite is related to the size of the spider. Spiders may also give a dry bite.

Species of spider responsible for the bite. Many spiders are harmless. In the

case of a serious spider bite, collecting the culprit may help in giving the correct treatment and a speedy recovery.

Use these symptoms as guidelines and be aware of pre-existing conditions that may complicate or add to the normal symptoms.

Dry Bites

As with many venomous creatures, spiders can bite but inject no venom whatsoever. Venom is the only defence that a spider may have towards predators.

They would never just waste their venom because of the time required to produce new venom and fill up their venom glands. Therefore, spiders only bite and inject venom as a last resort.

They can regulate the amount of venom injected. In some instances, a bite

from a spider may have very little or no effect. In such cases the spider injected very little venom. In other cases, however, the spider may inject a full dose. This occurs when the spider feels threatened.



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When to Seek Medical Intervention Most spider bites are not of medical importance and can be easily treated at home. However, there is a time when we all ask ourselves if we should be contacting a

professional medical doctor for advice about treatment or even hospitalisation? It must be noted that most doctors are not experienced in spider bites and

often misidentify spider bites and their treatment. If you have been bitten by a Button Spider (either Brown button spider or Black

Button Spider) then you should get help immediately. Signs and symptoms from Button spider bite present within 15-60 minutes and may be particularly

debilitating. Luckily, Button spider bites are painful, so the culprit is usually collected and identified.

In other kinds of spiders, the bite can be managed at home if you have the knowledge. If you are

consider yourself capable of medically treating a spider bite, you need only call a doctor if the situation deteriorates. If you feel you are not

capable of treating a spider bite yourself then as a first line measure, seek medical help at the first

sign of a spider bite or spider bite like symptoms. If the bite becomes infected, or you suspect that the bite is infected then go get

medical advice. If you have any pre-existing medical conditions that you think may be amplified by a spider bite then get medical help. If symptoms are more than

localised and consist of muscle cramps, headaches, rashes or any other symptom that causes discomfort, then get medical help.



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About the Author of this section Jonathan Leeming

Born in England, Jonathan immigrated to South Africa in 1984. Fascinated by

the smaller things in nature he started a lifelong exploration into the more misunderstood creatures.

Author of Scorpions of southern Africa, Co-author of The Bushveld – a

comprehensive field guide to the Waterberg, and the Sasol First Field Guide to Spiders and Scorpions. Jonathan is also a free-lance writer

who has published many articles in mainstream publications.

Jonathan spends his time giving lectures, training field

guides, writing about his beloved creepy crawlies and professional guiding.

Jonathan is an accomplished professional speaker,

photographer, travel and nature writer. In this course, he shares his intimate knowledge and enthusiasm of

southern African spiders in a unique and refreshing way.

http://jonathanleeming.com/



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Sensory Organs Most spiders have eight eyes, often in two rows of four eyes each. Spiders’ eyes are the most efficient of all the arachnids.

The eyes of many cursorial species have a well-developed tapetum that aids in

gathering light onto the retina and therefore improves night vision. The eyes of these species are often seen in the beam of a spotlight during night drives in the bush. It remains uncertain whether spiders can differentiate colour.

Hairs and slit organs on the legs of most species are used in the tactile location

of mates and prey. For the Labdiognatha species this tactile sense is of the utmost important. An exceptional tactile sense is necessary for interpreting vibrations on webs.



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Reproduction Correct mate recognition is important for spiders for if they make a mistake, it

is likely that they will be eaten by their so-called mate. Mate recognition is therefore accomplished by several tried and tested methods.

It is generally untrue that spiders eat their mates after copulation. This only takes place infrequently, and is usually accidental.

One method of mate recognition is the analysis of the pheromone cocktail left

behind on the dragline by a female. This allows the male to find out what the:

Species

Gender

Receptiveness

of the female are before he approaches her. Web-weaving spiders have a “Morse-code” system of mate recognition. A male will approach the web of a female and

give a series of tugs to the strands.

These tugs have a code that is unique to that species, and will be answered by the female if everything appears correct.

The male’s pedipalps are adapted into sex organs.

Sperm is collected in special sacs in the pedipalps, and these are introduced into the female’s genital opening. In some species, the pedipalps break off

the male, rendering him reproductively useless afterwards.

The eggs are only fertilised as they leave the female’s body. Up to three thousand eggs are

laid at a time in a silk casing, where the newly hatched young remain until they have undergone

their first moult.

After moulting, the spiderlings of many species are known to climb to the top of

the nearest high point and release a strand of silk into the air. Once the wind tugs the thread hard enough, the spiderling releases its hold and floats away using the

silk strand as a balloon. This ensures the dispersal of the species throughout the area.

On average spiders live for between one and two years. In some remarkable cases, though, captive individuals have been known to live as pets for more than 20

years. This illustrates the often harsh conditions of the wild as compared to the almost stress free environment occasionally provided by people.

spiders - wildlifecampus · the silk spinning apparatus of spiders is known as spinnerets. these...

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