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Spiders: Snare Specialists
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Did You Know...?
- …that spiders are not insects—insects have six legs, and a three-part
body; spiders have eight legs, and a two-part body.
- …that a single spider may kill as many as 2000 insects in its short lifetime.
Without spiders, we would be overrun with insects.
- …that spiders range in body length from 3 1/2 inches (in warm climates) down
to species that are almost microscopic.
- …that not all spiders make webs, but all produce silk,. Some use their silk
to make cases for their eggs, or to spin strands for ballooning—drifting long
distances on the wind.
- …that jumping spiders can jump up to forty times the length of their bodies.
- …that spider silk can be as sticky as glue or as slippery as ice, depending
on what the spider needs..
- …that all spiders have poison fangs, used to subdue their prey. The venom of
only a few (e.g., black widow, brown spider), is harmful to man, and is seldom deadly.
- …that the silk of certain spiders is the strongest natural fiber known; steel
drawn out to a similar diameter would not be as strong.
- …that spider silk is also elastic—some can be stretched to three times
its length without breaking.
- …that in most species, the female spider is larger than the male—sometimes
as much as 100 times larger.
- …that species of spiders which must hunt prey have excellent eyesight.
Some have eight eyes.
- …that spiders are found throughout the world; no climate is too rugged for
them. They have been seen at an altitude of 22,000 feet on Mount Everest—a
full mile above the vegetation line, and in caves two thousand feet below the earth's
surface.
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Spiders are one of the most numerous species inhabiting the
earth. Scientists have named about 34,000 species, but it is thought that these
represent only about one quarter of all the different spiders in the world. A
British naturalist took a spider census on a one acre plot in the English
countryside and determined that more than two million were in residence there,
either above or below ground.
Why so many spiders? It may be that our great Designer saw a
need for them in controlling the insect population. Spiders eat quantities of
insects—grasshoppers, mosquitoes, pesky flies, locusts, beetles, caterpillars.
A single spider may kill 2000 insects in a year. Without spiders, harmful insects
might take over our summer landscapes. Someone calculated that spiders in England
each year destroy insects equal to more than the weight of the human population of
the area!
Even spiders are not chance creatures but show highly
specialized design. They have jointed legs (a spider's leg has eight sections) and a
skeleton on the outside of their body. As the baby spider grows, its hard outer
skeleton splits and a new one takes its place (a process called molting). This may
happen as many as 10 or 12 times, and within a relatively short period of time
(the average life of a spider is less than a year).
Skilled Silkmakers
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All spiders make silk, and many use their silk to build webs.
Most accomplished among web-building spiders is the orb-weaver. Its webs, marvels
of geometric design, are real death traps for flying insects, and the snared prey
seldom escape. At the end of the day, the orb weaver spider often eats its web and,
working in darkness, builds a new one (in about an hour). Baby orb spiders spin
miniature versions of the same webs.
Shall we think that this tiny creature had to learn the art of
web-building by trial and error?—or shall we believe that it has been equipped
by its Creator with all the engineering skills and tools it needs to spin near perfect
silk strands which are marvels of strength. The web stgrands are also very elastic.
The finest strands can be stretched by at least a third without breaking!
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Orb Weaver Spider
Image courtesy of Wikipedia.org and Creative Commons (Attribution Sharealike 2.0) |
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Spider silk is no mean product. It can be as sticky as glue
(yet the spider itself never seems to get “stuck” in it) or as slippery
as ice. And it is one of the strongest natural fibers known. Steel drawn out to a
similar diameter would not be as strong. Why? because what looks like a single strand
of spider silk is not single at all but many strands drawn together to form a cable.
How does the spider make silk? The spider has six different
kinds of glands, each of which produces a different kind of silk for a different
purpose—one type for wrapping its prey, another for producing sticky globules,
another for making the cross strands of the web, etc. The spider is a true silk
specialist. Heavier cable-like silk strands are used to support the web. Lighter
weight strands make up the web itself.
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The spider forms the silk threads in 3 or 4 pairs of spinnerets
located at the end of its abdomen, which open to the outside through tiny spigots. A
single spinneret may open through thousands of spigots. As the spider spins silk, the
streams of silk from the different spigots unite into a single cable-like strand.
When starting a web, the orb spider attaches a strand of silk
to a weed stalk, porch railing, pole, or whatever, then drops down with the strand
attached to its body, crosses to the desired location and climbs up and pulls the
line taut from the point of beginning. This is called the bridge line. Once the
bridge line is up, the spider drops a plumb line to create one side, crosses back
to the first side, adds another plumb line, completing the frame with a lower bridge
line. Within this square this artistic weaver, without architect or blueprint,
constructs a perfectly proportioned web.
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Web of an orb spider |
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Then it is time for the spider to wait. Spiders are very patient.
Many spend most of their lives just waiting for the hapless insect to fall—or
jump, or fly—into its trap.
Immediately when an insect touches the web, the watching spider
springs into action. Examining its captive, it covers it with sticky silk, turning it
as on a spit as though to punish it before giving it a lethal bite and carrying it off
to a place of storage for later meals—unless the captive is a butterfly or moth.
If the spider finds a moth in its web, it bites the moth first, as though knowing that
the moth has remarkable ability for getting free of the web, due to its scales.
(How did the spider learn this wary tactic?)
Insects usually leave the web in need of repair.
The spider may repair it, or if the damage is too great, he simply abandons it,
rests awhile, then makes another web.
Some very large spiders in tropical climates produce silk in
huge quantities. A scientist once stripped 6 feet of silk a minute from one of these
spiders and stopped only after he had extracted 450 feet! A naturalist exploring the
jungles of Central America noted a large spider dangling on a line attached to a tree
limb more than a hundred feet above the ground. As he watched, the spider began taking
up the silken strand, reeling itself up into the canopy of the jungle. The spider
could take up the line, store it by consuming it, then recycle and reuse it.
Chance or Design?
Various types of spiders are variously equipped for their hunting
tasks. If the spider is a type that depends on its web-building skills, it has a
larger brain, keener sensitivity, and poorer eyesight. The highly sensitive legs of
the web builders can feel even very minute vibrations on their webs—that is how
they locate their prey. Spiders that seek prey by sight have keener eyesight and a
smaller brain. (Did the spider decide how much brainpower, sense of touch, or eyepower
it needed?)
Spiders that climb slippery leaves and branches have pads of
sticky hair on the bottoms of their feet to keep them from slipping.
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Crab spiders wait for prey on flowers, then use their legs to
grasp the victim and give it a lethal bite.
Jumping Spiders locate their prey, then pounce on it. These
spiders are able to jump very far and very accurately. If we could jump as far in
relation to our size, we could spring the length of a city block in a single bound.
Wandering Spiders have two claws on each foot. Between the claws
is a pad of hair, which gives them a firmer footing.
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Jumping Spider |
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Web building spiders have three claws on each foot. The middle
claw hooks over the silk threads of their webs.
Web building spiders have larger and more powerful jaws—
because they have to grab and hold their prey without the aid of a web.
What human hand has fashioned these wonders? What human mind
can even comprehend them all? Who will say there is no great Designer? Truly, the
hand that made even the lowly spider is Divine!
For Scientific Data in this Article, we are indebted to:
- The Book of Popular Science, Volume 2, pp. 259ff
- Marvels and Mysteries of Our Animal World, “Spiders,” by L. Hemingway, published by the Reader's Digest Association, Pleasantville, New York, pp. 101-103
- Zoobooks, “Spiders,” published by Wildlife Education, Ltd., March, 1988
- Encyclopedia Britannica, Fifteenth Edition, 11:94-95; 13:924ff.
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