Spiders, scorpions, ticks, and mites have two body parts
and four pairs of legs. They breathe using lung books (that look like an open
book) in the abdomen. The front part of the body, known as the cephalothorax,
bears the legs and two pairs of mouthparts: the chelicerae, which are like
either pincers or fangs, and the pedipalps, which look like either legs or
claws. Most arachnids live on land, but some live in water.
Most arachnids are predators, but some scavenge for food and a few
mites are parasitic (live on another animal and feed off that animal). There
are 75,500 species of arachnid, in 12 orders, including the following three
main ones.
(scorpions)
Features: predators, sting-bearing
tails, large, claw-like pedipalps, bear live young
(mites,
ticks)
Features: body not distinctively
segmented, many are pests and parasites
(spiders)
Features: mostly eight-eyed, able to
produce silk
A tick’s soft, flexible abdomen can expand to 10 times its
normal size as the tick sucks in blood with specialized piercing and sucking
mouthparts. The tick fastens itself to a sheep while it drinks in blood, then
drops to the ground. When it needs more food, it attaches itself to another
animal that is passing by.
The imperial scorpion is one of many arachnids that care for their
young. A female scorpion carries about 30 young on its back until they have
moulted (grown a new, larger skin) for the second time. The scorpion has a
hard, black carapace (shell), large claws, and a poisonous sting.
A spider’s spinnerets produce liquid silk that hardens in the
air. Many spiders spin a web with this silk, to catch prey. When an animal gets
caught in the web, the spider wraps it in silk and kills it with venom. Spider
silk is the strongest-known material – if a web were made with silk
threads the diameter of a pencil, it would be strong enough to stop a plane in
flight.
