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to today’s info. In our world there is lots of animals and livings and each one
have their own Secrets and beauties. Today we are going to know about a spider
that has a big horn. Yes a big horn spider
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Classification
Kingdom: Animalia Phylum: Arthropoda
Subphylum: Chelicerata Class: Arachnida
Order: Araneae Infraorder: Araneomorphae
Superfamily: Araneoidea Family: Araneidae
So let’s know about him, spiders
are among the craftiest and most beautiful of arthropods, entirely undeserving
of their maligned reputation. Some signal their presence with massive horns or
brilliant colors, others attempt to blend into the scenery.
Many spin intricate
traps of sticky silk, but some chase their prey -- or ambush it, bursting out
of burrows hidden beneath Earth's surface.
With its massive antenna-like horns, the spiny Macracantha
arcuata looks like some sort of WiFi-equipped gadget. Nobody is really sure
what purpose the horns actually serve, but it's possible that they are mostly
for show, to make the spider look more intimidating to predators. Orb-weaver spiders or araneids are members
of the spider family Araneidae. They are the most common group of builders of
spiral wheel-shaped webs often found in gardens, fields and forests.
"Orb" was previously used in English to mean "circular",
hence the English name of the group. Araneids have eight similar eyes, hairy or
spiny legs, and no stridulating organs.The family is cosmopolitan, including many well-known large or
brightly colored garden spiders. With 3122 species in 172 genera worldwide,
Araneidae is the third-largest family of spiders (behind Salticidae and Linyphiidae).
Araneid webs are constructed in a stereotyped fashion. A framework of nonsticky
silk is built up before the spider adds a final spiral of silk covered in
sticky droplets.Orb-webs are also produced by members of other spider families.
The long-jawed orb weavers (Tetragnathidae) were formerly included in the
Araneidae;
they are closely related, being part of the superfamily Araneoidea.
The family Arkyidae has been split off from the Araneidae.The cribellate or
hackled orb-weavers (Uloboridae) belong to a different group of spiders.
Their
webs are strikingly similar, but use a different kind of sticky silk. Generally, orb-weaving spiders are
three-clawed builders of flat webs with sticky spiral capture silk. The
building of a web is an engineering feat, begun when the spider floats a line
on the wind to another surface. The spider secures the line and then drops
another line from the center, making a "Y". The rest of the
scaffolding follows with many radii of nonsticky silk being constructed before
a final spiral of sticky capture silk.The third claw is used to walk on the nonsticky part of the
web. Characteristically, the prey insect that blunders into the sticky lines is
stunned by a quick bite, and then wrapped in silk.
If the prey is a venomous
insect, such as a wasp, wrapping may precede biting and/or stinging. Araneids species either mate at the central hub of the web,
where the male slowly traverses the web, trying not to get eaten, and when
reaching the hub, mounts the female; or the male constructs a mating thread
inside or outside the web to attract the female via vibratory courtship, and if
successful, mating occurs on the thread.In the cannibalistic and polyandrous
orb-web spider Argiope bruennichi, the much smaller males are attacked during
their first copulation and are cannibalized in up to 80% of the cases. All
surviving males die after their second copulation, a pattern observed on other
Argiope species. Whether a male survives his first copulation depends on the
duration of the genital contact: males that jump off early (before 5 seconds)
have a chance of surviving, while males that copulate longer (greater than 10
seconds) invariably die.
Prolonged copulation, although associated with
cannibalism, enhances sperm transfer and relative paternity. Sexual dimorphism refers to physical
differences between males and females of the same species. One such difference
can be in size.Araneids often exhibit size dimorphism typically known as
extreme sexual size dimorphism, due to the extent of differences in size. The
size difference among species of Araneidae ranges greatly. Some females, such
as those of the Nephila pilipes, can be at least 9 times larger than the male,
while others are only slightly larger than the male. The larger size female is
typically thought to be selected through fecundity selection,the idea that
bigger females can produce more eggs, thus more offspring.
Although a great
deal of evidence points towards the greatest selection pressure on larger
female size, there is some evidence that selection can favor small male size as
well.Araneids also exhibit a phenomenon called sexual cannibalism, which is
commonly found throughout Araneidae.Evidence suggests a negative correlation
between sexual size dimorphism and incidences of sexual cannibalism. Other
evidence, however, has shown that differences in cannibalistic events among
araneids when having smaller or slightly larger males is advantageous.
The oldest known true orb-weaver is
Mesozygiella dunlopi, from the Lower Cretaceous. Several fossils provide direct
evidence that the three major orb-weaving families, namely Araneidae, Tetragnathidae
and Uloboridae, had evolved by this time, about 140 million years ago.They
probably originated during the Jurassic (200 to 140 million years ago). Based
on new molecular evidence in silk genes, all three families are likely to have
a common origin.The two families, Deinopoidea and Araneoidea, have similar
behavioral sequences and spinning apparatuses to produce architecturally
similar webs. The Araneidae weave true viscid silk with an aqueous glue
property, and the Deinopoidea use dry fibrils and sticky silk. The Deinopoidea
(including the Uloboridae), have a cribellum – a flat, complex spinning plate
from which the cribellate silk is released.
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