Arachnid, also known as class Arachnida, any member of the arthropod group including spiders, longhorns, scorpions, mites, and ticks (in the subclass Acari), as well as lesser-known subgroups.
Only some species of Arachnids are of economic importance – for example, mites and ticks that transmit diseases to humans, other animals, and plants.
Well many arachnids are more like creeps to most of us, so we may wonder what role do they have in the ecosystem – can they be of importance? you may ask, yes they are.

General Characteristics

A common characteristic is the absence of antennae and a body consisting of a cephalothorax and abdomen, the latter may appear as a single part without divisions.

The cephalothorax bears four pairs of walking legs and 6-8 eyes raised on tubercles.

Head appendages include chelicerae, which resemble jaws with claws and venomous duct openings at their ends. The basal part of the pedipalps has both foraging and sensory functions.

Arachnida are air-breathing arthropods whose body is divided into two parts: the cephalothorax, which includes the fused head and thorax, and the abdomen.

The abdomen may be segmented or unsegmented. In mites and ticks the whole body is fused and forms a sac.

The head appendages are highly altered. The whiskers are lateral and the eyes, when present, are simple and sessile.

Adults have four pairs of ambulatory legs, which are attached to the cephalothorax.

The first stage of development is the larva, which has three pairs of legs. The respiratory organs are represented by either book lungs or trachea.

The sexes differ in structure and metamorphosis is incomplete. The immature individuals resemble small adults.

Arachnids absorb fluid from their prey using a ‘sucking stomach’. The mouth organs serve either to crush the prey and absorb liquid portions, or to puncture and cut through host tissue to obtain blood .

The oral organs consist of a pair of chelicerae located in front of the mouth opening; a pair of pedipalps located on the sides of the mouth or immediately in front of them.

Some parasitic species have a structure called the hypostoma, which is located immediately below the mouth opening.

The chelicerae differ structurally in different orders. In spiders (Araneida), each chelicera consists of a large basal segment and a claw-shaped terminal segment.

Spiders use these structures to capture and kill their prey. The venom gland is located near the tip of the claw. Parasitic species (e.g. mites) use the pincers as stabbing and cutting tools.

Pedipalps are similar to legs and have 4-6 segments in all groups.

In spiders, the pedipalps of 4 male spiders are highly modified into very specialized insemination organs for females. Among many mites they are the defence of highly developed stabbing organs .

Roles Of Arachnids

Arachnids range in size from tiny ticks measuring 0.08 mm (0.003 in) to the huge African scorpion Hadogenes troglodytes, which can be as long as 21 cm (8 in) or more.

In appearance they range from short-necked, round-bodied mites and tick-equipped scorpions with coiled tails to graceful, long-legged dadgies and sturdy, hairy tarantulas.

Spiders (order Araneida), daddy longlegs (order Opiliones), false scorpions (order Pseudoscorpiones), and ticks and mites (subclass Acari) are nearly worldwide in distribution.

Spider

However, most arachnids are rarely seen, as they inhabit foliage, bedding or soil. The most common of these are the fruticose lichen Cladonia rangiferina (deer moss) and other tundra lichens, which serve as food for reindeer, caribou, musk oxen and other Arctic tundra wildlife.

Although many arachnids actively search for their prey, lying in wait is a more common method.

In warm regions, some groups (e.g. whiptail scorpions, tailless whiptail scorpions, scorpions, sun spiders and tarantulas) live for more than one year.

In spiders, silk is stored as a viscous liquid in the silk glands, which are located within the abdomen.

As of recent, spider webs have been discovered as an additional material that can be used in fishing nets, surgical stitches and adhesives because it contains natural antiseptics, which allows its use for medical purposes.

The venom of spiders (40,000 different species are known) serves as chemical material for creating new insecticides.

Spiders are predators that feed mainly on insects. Therefore, spiders benefit humans by keeping some insect populations under control.Spiders are obligate predators, meaning they must eat other animals to stay alive.

By limiting the population on unwanted pests around the household, spiders can actually decrease the risk of many common deceases that people can obtain. An example of this is when spiders consume mosquitoes, they are highly reducing the risk of spreading malaria.

It is estimated that one spider can eat up to 2,000 insects in a year. Due to their wide appetite, many spiders play an important role in their communities by regulating the density of other invertebrate herbivores and predators. When you consider the diversity of food species they consume and their huge numbers, spiders are among the most important invertebrate predators in terrestrial ecosystems.

Ticks and mites are important medically due to their ability to carry disease . Scorpions are studied for scientific research in most universities.

Scorpion venom is used for pharmacological, biochemical and immunological research.

This may sound abnormal, but many places in the world actually consume spiders in their diets. An example of this lye’s in Cambodia where humans actually fry and consume spiders on a regular basis.

Ticks and mites feed mainly on fluids derived either from living animals or plants or from decomposing organic matter.

Predatory mites prey on nematodes, springtails, other mites, and the larvae of insects.

Order Of Arachnids