The branch of zoology that focuses on the scientific study of arachnids, a class of joint-legged invertebrates that includes spiders, scorpions, ticks, mites, harvestmen, and others.
Arachnology focuses on understanding these creatures’ anatomy, behavior, ecology, evolution, and their roles in ecosystems.
This field is crucial for various practical applications, including pest control, medical research, and environmental monitoring.
Scientific Classification
• Kingdom Animalia
• Phylum Arthropoda
• Clade Arachnomorpha
• Subphylum Chelicerata
• Class Arachnida
Arachnids are joint-legged arthropods of the class Arachnida, belonging to the subphylum Chelicerata.
They include spiders, scorpions, ticks, mites, pseudoscorpions, camel spiders, whip scorpions, and tailless whip scorpions.
The name ‘Arachnida’ is derived from the Greek word ‘Arachne,’ referring to the myth of the egotistic human weaver Arachne, who turned into a spider.
Unlike insects (subphylum: Insecta), almost all adult arachnids possess eight true appendages attached to their cephalothorax, which characteristically have six legs. While most arachnids, like spiders, scorpions, and harvestmen, are strictly terrestrial, sea spiders and water mites are fully aquatic.
About 1,50,000 arachnid species are found worldwide (of which about 51,000 are spiders) and are grouped into 16 extant orders.
Arachnids are animals that have:
• Eight walking legs
• One or two main body parts
• Often predatory habits
• Simple eyes
• A skeleton outside the body
Arachnids have a body usually divided into two parts, the prosoma (cephalothorax or prosoma) and opisthosoma (abdomen).
This contrasts with insects which have their body divided into three parts: head, thorax and abdomen.
Mites and harvestmen bodies are less obviously divided, having the prosoma (thorax) and opisthosoma (abdomen) fused together.
The prosoma carries six pairs of appendages: the four pairs of legs, pedipalps and chelicerae.
Pedipalps and chelicerae are modified in the different arachnid groups and may form spiny grasping limbs or lobster-like claws.
The prosoma also carry varying numbers of eyes.
Virtually all arachnids are terrestrial.
However, some spiders, mites and palpigrades occur in both fresh water and intertidally on the seashore in shallow salt water. Halacarid mites are known from 4000m depth seawater.
Key Areas of Study in Arachnology
1. Anatomy and Physiology:
Arachnids have distinct body structures, typically divided into two main parts: the cephalothorax (combining the head and thorax) and the abdomen.
They have eight legs and specialized mouthparts called chelicerae for feeding, along with pedipalps that often serve as sensory or reproductive appendages.
2. Ecological Role:
Arachnids play a critical role in ecosystems as predators, helping control insect populations and other small organisms.
Some, like ticks and mites, are parasitic and can impact human and animal health by spreading diseases.
3. Behavioral Studies:
Arachnologists study behaviors like web-building in spiders, mating rituals, and prey capture strategies, which offer insights into their survival techniques and adaptations.
4. Evolution and Biodiversity:
The diversity of arachnids, with over 100,000 described species, showcases their evolutionary success and adaptation to various environments worldwide.
Importance of Arachnology
1. Medical Applications: Understanding the venom of spiders and scorpions has led to the development of medicines and antivenoms.
2. Agricultural Impact: Some arachnids act as natural pest controllers, reducing the need for chemical pesticides.
3. Environmental Indicators: Arachnids are sensitive to environmental changes, making them valuable bioindicators in ecological studies.