Invertebrate Zoology: Textbook - T. A. Dauda 2014

Metazoa
Arthropods
Subphylum Chelicerata - Class Arachnida - Order Acarina

These are small, sometimes microscopically tiny arachnids with highly diverse lifestyles. Some mites and ticks are secondarily aquatic, while many are parasites of plants and animals. About 10,000 species have been described, many of which are of significant practical importance. Ticks and mites exhibit various types of body segmentation, though most often their bodies are completely unsegmented.

The segments of the chelicerae and pedipalps are usually fused into a more or less mobile capitulum or gnathosoma, functioning as a piercing-sucking Mouth apparatus.

The majority of mites and ticks breathe through tracheae, while some lack respiratory Organs entirely and respire through their entire body surface. Their development is typically characterized by metamorphosis. A fertilized egg hatches into a larva with 3 pairs of legs, which then develops into an immature nymph possessing 4 pairs of legs, just like the adult. There are usually several nymphal stages.

Mites and ticks cause immense harm as parasites of humans, domestic animals, and crops, as well as vectors of many dangerous pathogens and pests of stored food products.

Among human parasitic mites, the itch mite (Sarcoptes scabiei) (Fig. 53) deserves special mention; it lives in the Skin of humans and various mammals and is extremely small. The Hair follicle mite (Demodex folliculorum) inhabits human Sebaceous Glands and hair follicles, causing pustular acne.

Even greater damage is caused by ixodid and argasid ticks, which lead an ectoparasitic lifestyle. These ticks act as vectors for highly dangerous diseases affecting humans and livestock, such as tick-borne typhus and relapsing fevers, tick-borne encephalitis, tularemia, and bovine piroplasmosis.

Widespread species include the taiga tick (Ixodes persulcatus) (Fig. 54), which is particularly abundant in the forests of the Russian Far East, and the castor bean tick (Ixodes ricinus), found throughout Europe.

Adult ticks typically inhabit grass and shrubs, from which they ambush humans and large mammals. Females engorged with Blood drop off the host and lay eggs in the leaf litter. These hatch into larvae that feed on the blood of lizards, birds, rodents, insectivores, and the like.

Engorged larvae retreat into the soil to molt. The resulting nymphs then prey on larger animals—hares, squirrels, chipmunks, and so forth. Upon completing their metamorphosis, the primary hosts for adult ticks are humans, cattle, moose, deer, and large predators. Thus, ticks of the genus Ixodes, like other members of the ixodid family, utilize multiple hosts throughout their life cycle. However, in some species, the larvae and nymphs inhabit a single host while the adults attack another.

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Fig. 53 Itch mite (Sarcoptes scabiei), female

Fig. 54 Taiga tick (Ixodes persulcatus)

Several forms spend their entire lives on a single host.

A large group of mites parasitizes plants, inducing The formation of abnormal growths known as galls.

Some mites serve as intermediate hosts for tapeworms. Many others infest and ruin stored grain and flour reserves.

Soil mites (such as Oribatida) feed on plant debris, participating in the decomposition of organic matter and ultimately contributing to soil formation.

QUESTIONS FOR SELF-assessment and review:

1. Where do arachnids live?

2. What are the General Structural Features of arachnids?

3. What organizational and ecological features characterize scorpions, harvestmen, spiders, and mites/ticks?