Unlike the araneomorphs, however, whose life is over in a year or so, mygalomorphs live for many years (15-25) and most don't reach maturity for 5-7 years. Once mature, the male spider has a relatively short life (maximally 3-6 months). His purpose is simply to locate a female and mate. Some, like the Redback Spider (Latrodectus hasseltii), die during or just after the mating, voraciously consumed by the females; others escape but die naturally soon after. Female mygalomorphs live up to 25 years, each year they shed their outer skin (moult) and mate; whereas female araneomorphs like their males reach maturity, mate, construct egg sacs and die.
1. Silken Experiments. In araneomorph spiders, evolution proceeded rapidly in three major characters: silk, claws and eyes. Silk spinning began to be explored. Each pair of spinnerets developed different kinds of silk glands with different functions and the spiders control that. Some silk is used only for the egg sac, some is only used to build the main web lines and some for the sticky drops that trap the prey. Young araneomorph spiders are smaller and lighter and as the liquid silk is pulled from the spinnerets it turns to the complex strand we see. As the strand lengthens in the wind, updrafts pull more silk from the spider until finally, the lift so created carried the spider skyward. Many young spiders disperse by this means called ballooning. Ballooning spiders have been recorded as high as the stratosphere.
Diverse Uses. Most spiders use silk as part of a snare to trap their prey. Often the snare is the complex and beautiful webs that we so often see. Some have found special trapping techniques. The Bolas spiders (Araneidae: Mastophorinae) spin a specially scented drop of silk on the end of a line. The scent is that of a female moth which attracts the male moth that is struck by the whirling silken drop. The Crab spider Phrynarache uses a variation on that in building a stinking smelly pad of silk to which flies are attracted. The Ray Spiders (family Theridiosomatidae) build a circular web with a line at right angles from the centre. The web is pulled back into a cone and the cone "fired" at insects that stray within the cone. Apart from its use in trapping prey, spider silk also used to wrap and subdue prey. Most spiders when they walk leave a strand of silk (dragline) which acts as a safety rope should they fall or jump.
How did the spider get the web over there? A variation on ballooning is that web-building spiders pay out silk with a special sticky silken drop on the tip. The wind carries the strand until finally it sticks to a nearby object whereupon the spider takes the line, attaches it firmly beside itself and proceed to cross the web and lay strengthening web and the beginning of the basic triangle. You can guess that the spider must pass along its own web more than once in construction. That only makes the span stronger.A spiders web can take about one hour to build, depending on the complexity. Silk is a strange and complex chemical and requires considerable energy to make. Hence, some spiders partially reclaim some of that silk by pulling down the web in the early dawn and digesting it. No doubt they also get benefit from consuming the tiny insects and even pollen that has stuck to the web through the night.
2. 'These boots were made for walking'. All spiders have 8 legs in 4 pairs that arise from the sides of the cephalothorax. One of the main functions of the legs is walking. However, the legs are often the first part of the spider to interact with the environment, prey and predators. Hence, many sensory structures are found on the legs. Some are raised as delicate hairs above the leg surface; others are chemical sensors on the cuticle surface and a few are internal detectors of cuticle stress. Also, the bases of the legs and palp (coxae) may be involved in generating sound and /or the discharge of waste products. In addition, legs may have ornamental structures or colour patterns that improve the mimicry of other organisms like wasps or ants or simply aid camouflage. In some trapdoor spiders (Mygalomorphae), the legs may be especially modified for burrow living, as is the case with the genus Conothele which has a reinforced saddle on the upper surface of the third tibia; that saddle is used to brace the spider more firmly against the walls of its burrow making it harder to dislodge by predators. In male mygalomorphs, the first and sometimes also the second leg bears structures on the tibia and metatarsus that are critical to ensure the safety of the spider through the mating process. During mating, males are often poised precariously under the opened fangs of the female. Spines on the legs lock open the female's fangs, preventing him from being "accidentally" killed during mating. Finally, web-building spiders use the vibrations in the web and detected through the legs as long range sensors. When prey strikes a web, it causes vibration. The spider responds to the vibration much as a fisherman with a fishing line. It tugs back to see whether the prey is alive or whether a leaf or stick have fallen into their web. Spiders with these extended methods of sensing are effectively blind; their eyes function primarily to detect movement, light and darkness. In this case, their eyes are their legs.
Perhaps one of the most dramatic changes, however, that evolved in spiders was the ability to climb smooth vertical surfaces. This occurred through the development of special flattened hairs with many fine hairs on them. Those hairs greatly increase the surface area over which the tip of spiders' legs contact the ground. The hairs occur both on the underside of the legs but the biggest improvement seems to be in those in which the hairs developed as dense tufts below the claws. Huntsman spiders (family Sparassidae) are a very good example of claw tufted spiders. See how easily they climb the wall and even walk upside down on the ceilings. So this was the start of another explosion — the development of claw tufts — that spawned another group of spiders.
3. The Eyes have it. The original complement is eight similar eyes and they formed a roughly rectangular group in two rows and that is a common condition in many spiders. Some spiders may have lost from one pair of eyes to all eyes, as is often the case in cave spiders. Spiders with that original eye configuration had poor vision; their eyes function primarily to detect movement, light and darkness. However, major changes occurred in the eyes — mostly in relative position and size. In many groups, the front row of eyes became small and the back row became bigger. The viewing angle of the back row improved to allow the spider to see to the side and back without turning. Many active hunting spiders like the Wolf spiders (family Lycosidae) and Water spiders (family Pisauridae) developed such eyes and are able to hunt even at night. Their big back eyes "shine" or reflect light when a torch light is held close to your eyes and pointed at the spider.
In some spiders, however, the front eyes became the big ones and perhaps one of the more spectacular is Net-casting spider (Deinopis, family Deinopidae) who stared at you when you started the Araneomorphae part of the key. Deinopis is most unusual among the web-building spiders as they alone have explored the massive enlargement of the eyes. An ancestor of the orb-weaving spiders, Deinopis builds a magnificent rectangular blue web which she holds and twirls with truly blinding speed around hapless moths that stray near her. Her hunting accuracy is possible only because of her sight.
But the development of giant front eyes is "owned" by the Jumping spiders (family Salticidae) whose vision is much studied and renowned. In fact, one Australian Jumping Spider, Portia fimbriata, has been found to have telephoto vision second only to the eagles. With its superior vision and painstaking "patience", it stalks spiders on their own webs. Jumping spiders have remarkable courtship behaviours in which the male raises and lowers legs in a semaphore fashion, showing his gaudy markings and signalling his intentions to the female. She in turn responds.
With their powerful vision, Jumping spiders are able to detect and launch upon prey from many times their body length. In the Jumping spiders, the synthesis of the two evolutionary explorations — the claw tufts and strong vision — come together in a spectacular way and many species quickly evolved. The family of Jumping spiders is one of the richest families in species and genera. Remarkably, many still have evolved mimicry and the ant-mimicks (Myrmarachninae) enjoy the rich plunder of seemingly neverending ants, especially in the tropics.
Spiders are one of the most seen and least known but most feared of the invertebrates
of Australia. Their full diversity is far from being mapped. Last estimates
are that the real number of species in Australia is around 10,000, i.e.,
about four times that presently named. That estimate was, however, conservative.
In a recent study on Australian White-tailed spiders (Lamponidae), Platnick
(2000) rebuilt the family and took it from 24 species (in 6 genera) to 186
species (in 21 genera). That continues to verify Raven's (1988) prediction that
the real number of species is closer to 7 times higher than present. Although it
seems academic, the question takes on an altogether different hue when it is
realised of these 10,000 or so species the venoms of only about 50 are well
known. Most are probably quite harmless but nevertheless the complex composition
of the venom may well again serve as a useful model for a drug or
insecticide.
Most native bush areas include about 300-400
spider species (about 50-100 occur in bushy suburbs). Some species are quite
tiny (totally little bigger than the full stop in a sentence) but remarkably
shaped. Despite their small size, those "micro" spiders are rare, exciting and
belong to families either endemic to Australia or southern continents. Indeed,
one family, Archaeidae or Pelican spiders were first discovered fossilised in
Baltic Amber but later found alive and well through coastal Australia, New
Zealand, Madagascar and Chile.
Diversity in different habitats
Different forests are habitats to different suites of species. The most diverse
and bizarrely populated forests are those of montane rainforests of south-east
Queensland and northern New South Wales where ancient species attract international
attention. Here the diversity on each mountaintop is relatively low, perhaps
200-300 species. However, of those species, many are endemic or known only from
that mountaintop. So the overall spider diversity in, for example, the entire
Wet Tropics Area of North Queensland, may total over 2000 species. In contrast,
in habitats least known for spiders (eucalypt forests, bottle tree scrubs, heath,
grasslands, mangroves and deserts) the diversity in any one may approach 400
species but those species may be widespread and hence when a number of such
areas (as in the case of the Wet Tropics) are surveyed the total diversity may
not exceed 800 species. Glamorous rainforests long distracted us from these
apparently leaner pickings. However, such forests, although perhaps not evidently
rich, have fostered high rates of speciation and different species have evolved
in the comparatively small geographic distances between forests.
Diversity in Microhabitats
Of course, the number of species and spiders each forest can support is related
to the diversity of three-dimensional microhabitats — because many spiders,
even the smallest, build webs, some in the cracks in the soil. Hence, about
one half of the diversity in a forest occurs in the leaf litter or below it.
In forests dominated with small-leaved trees (e.g. monocultures & needles
of introduced pine forests), the litter has no vertical space and hence is depauperate.
On the other hand in wallum, large-leaved Banksias support fewer species in
the foliage than smaller-leaved Melaleucas. Where, then, is the diversity in
spinifex? It is deep below the needles just above the soil and there, too, it
approaches the 300 species mark although finding them is both painful, hot and
arduous. In grasslands, the diversity is on the ground around the base. Our
least known and most neglected habitat is mangrove and wetlands. However much
we would like to advance on this new frontier we are restrained by human resources.
Despite the continuing pressure of our knowledge of species disappearing as
we speak, the most threatened and endangered of species are those who study
and name them, taxonomists. Good taxonomy, like that first mentioned, can be
done in a number of ways but the least popular with most (but the users!) are
very large (300 page) all-encompassing monographs that take an ferocious amount
of effort and dedication and the nett result is only one paper. Australia has
a mere handful of paid spider taxonomists but most are beleaguered by large
collections and many new species so we must resort to getting help overseas.
Even if it is not a new species, it can be a deep and complicated detective work to find out which species it is. In spiders, for example, there are over 34,000 species and some have travelled with humans as they colonised different parts of the world. So finding out the name of spider you found in Australia may require a lot of study of scientific papers on European spiders which may be written in German, French, Polish, Russian or even Japanese. But equally, the original specimen on which a species is based (holotype) was often collected by European collectors in the 19th century and the specimens are in European museums. Hence, in many cases, you must visit these museums and study the collections there. These can be exciting expeditions of discovery as you may discover holotypes long thought to be lost and ressurect a species from scientific anonymity.
Taxonomy also involves understanding the higher classification of animals and plants. A group of species is called a genus. A group of genera (plural of genus) is called a tribe. A group of tribes is a subfamily. So the heirarchy of names for, say, a Brush-footed trapdoor spider is like this:
However, we usually only use the two part or binomial name, Seqocrypta jakara Raven, 1994. Note that the genus name always begins with a capital letter but the species name does not and both are usually in italics. The name and year after that are the author of the species and year in which the species name was formally published; if they are in brackets it just means that the species has been moved to a different genus to which its author placed it.
Often a new genus is found, especially in invertebrates, and that requires determination of its relationships, i.e. where in the many families does it belong, why does it belong there and what is is closest relatives. One commonly used and widely accepted method used to answer these questions is cladistics. Using cladistics, we look at relationships usually the characters that are special or apomorphic to the species, genus, family; the groups are formed by those animals who share the most number of apomorphic characters. Because there so many different characters (each character is an evolutionary change or step) and so many species, scientists must now use computers to do these classifications. The rule that the computer uses is that it must find the solution with the fewest number of changes; that is called parsimony. Finding the fewest number of steps is a bit like trying to find the shortest way to join all the houses in a city into a electric power grid — there are literally billions of possibilities which the computer must assess to find the shortest.
We can get some understanding of the evolution of the animal through its relationships and that search can be one of the most exciting. We may discover an animal that breaks all our theories about what belongs to the family groups. It may have parts of one family and parts of another. Here the "fight" begins. We must form new theories about how evolution occurs and present such a strong argument to many will agree.
How names are constructed
The name of an animal basically consists of two parts — the species name
and the genus name. The species name is a little like a christian name but it
refers to a group of animals not just one individual. The genus name is a little
like the father's name. For a person called Geoff Smith then the genus name
is Smith and the species name is Geoff. When we form new scientific names, however,
we must not use a genus name that is already used in the animal kingdom. That
can be very difficult also because many people use Latin or Greek words
or names of Gods or combinations of them. Many are now using aboriginal names
for animals. We usually name animals using one of these combinations:
by adding to or rearranging part of an existing name, based on special parts
of the animal, based on the place from which it came, or to honour the person
who collected it or a scientist.
Raven, R.J. (1988). The current status of Australian spider systematics, pp. 37-47. In, Austin, A.D. & N.W. Heather, eds. Australian Arachnology. The Australian Entomological Society, Misc. Pub. 5.: Brisbane.