The class Arachnida is a group of more than 100,000 species, including spiders, scorpions, ticks, and mites. Most arachnids are adapted to kill their prey with venomous gills, stingers, or fangs. Like crustaceans, arachnids have a body divided into a cephalothorax and an abdomen.

Attached to the cephalothorax are 4 pairs of legs, a pair of chelicerae, and a pair of appendages called pedipalps. The pedipalps help chewing; in some species, the pedipalps are specialized to perform other functions. Arachnids undergo incomplete metamorphosis. The class Arachnida includes 3 orders of medical importance:

1. Order Scorpions

2. Order Araneae (spiders)

3. Order Acari (ticks and moths)

scorpio

Scorpions are a family group of arachnids whose pedipalps are modified into pincers. Scorpions use these pincers to manipulate their food and tear it apart. Scorpions’ venomous stings are used primarily to stun prey, and less often for self-defense. The stinger is found in the terminal segment of the body, which is thin towards the end. The elongated, jointed abdomens of scorpions are distinctive; in most chelicerates the abdominal segments are more or less fused and appear as a single unit. Adults of this order of arachnids range in size from 1 to 18 centimeters. There are some 1,200 species of scorpions, all terrestrial, found throughout the world, though they are common in tropical, subtropical, and desert regions. Scorpion courtship is elaborate, with spermatophores attached to a substrate by the male and then collected by the female. Young are born alive, with 1 to 95 in a given liter. Scorpions differ from spiders in two ways. Scorpions have greatly enlarged pedipalps, which they hold in a forward position. They also have a large stinger on the last segment of the abdomen. Most scorpions hide during the day and hunt at night. Scorpions grab their prey with their pincer-like pedipalps. Then the tusk injects paralyzing venom, the chelicerae tears the prey apart, the animal is ingested, and digestion begins. Only a few species have a stinger that can be fetal to humans. They do not bite a man unless they are attacked.

pathogenicity

Local bite symptoms include severe pain, inflammation, and swelling. Sweating, nausea, and vomiting are common systemic symptoms. In severe cases, muscle spasms and seizures can occur. The fatal outcome is caused by respiratory failure, pulmonary edema, and shock.

control

insecticide spraying

spiders

There are about 25,000 named spider species (order Araneae). These animals play important roles in all terrestrial ecosystems, where they are particularly important as predators of insects and other small animals. Spiders hunt their prey or trap it in webs. The silk in cobwebs is formed from a fluid protein that is expelled from spinnerets, modified appendages on the back of the spider’s abdomen. Spiders have venom glands running through their chelicerae, which are pointed and used to bite and paralyze their prey. Some members of this order, such as the black widow spider (Latrodectus mactans), the Australian black widow spider (Latrodectus seville), the scarlet spider (Latrodectus tredicimguttatus), the brown recluse (Loxosceles reclusa), the tarantula (Lycosa singoriensis), have stings that are venomous to humans and other large mammals.