"Animal" - what is it, definition of the term
The term designates a multicellular eukaryotic organism that obtains nutrients by consuming organic matter, possesses specialized tissues, and exhibits motility at some life stage; within this broad category, tick, bug, louse, and flea represent arthropod members that are ectoparasitic, characterized by segmented bodies, jointed appendages, and adaptations for feeding on the blood or tissues of vertebrate hosts.
Detailed information
Ticks are arachnids that parasitize vertebrate hosts to obtain blood meals. Their life cycle includes egg, larva, nymph, and adult stages; each active stage requires a blood source. Saliva contains anticoagulants and immunomodulatory compounds, facilitating prolonged feeding and pathogen transmission. Common disease agents carried by ticks include Borrelia spp. (Lyme disease), Rickettsia spp., and Babesia spp.
Bugs, specifically true bugs (order Hemiptera), exhibit piercing‑sucking mouthparts adapted for extracting plant sap or animal fluids. Many species possess scent glands that release defensive chemicals. Agricultural impact is significant: aphids, stink bugs, and shield bugs can damage crops through direct feeding and vectoring plant pathogens such as phytoplasmas.
Lice are obligate ectoparasites of mammals and birds. They belong to the order Phthiraptera and are divided into chewing and sucking forms. Chewing lice consume epidermal debris, while sucking lice ingest blood. Infestations cause irritation, skin lesions, and can facilitate secondary bacterial infections. Human body louse (Pediculus humanus corporis) is known for transmitting epidemic typhus, trench fever, and relapsing fever.
Fleas are small, wingless insects (order Siphonaptera) that specialize in hematophagy. Their laterally compressed bodies enable movement through host fur. Life stages comprise egg, larva, pupa, and adult; the latter requires a blood meal to reproduce. Flea saliva contains anticoagulants and anesthetic agents, allowing stealthy feeding. Key disease vectors include Yersinia pestis (plague) and Rickettsia spp. (murine typhus).
Key characteristics shared by these four groups:
- External parasitism on vertebrate hosts
- Specialized mouthparts for fluid extraction
- Complex life cycles with multiple developmental stages
- Capacity to transmit microbial pathogens
Control measures focus on environmental sanitation, host treatment with insecticides or acaricides, and monitoring of vector populations to reduce disease risk.