Ticks

Definition

Parasitic arachnids of the order Ixodida, within the superorder Parasitiformes. Adults possess a fused gnathosoma (capitulum) bearing piercing mouthparts and a sac-like idiosoma that expands markedly during blood-feeding. All post-larval stages are obligate hematophages of vertebrates, with many species serving as vectors of bacterial, viral, and protozoan pathogens. Hard ticks (family Ixodidae) bear a dorsal scutum and exhibit prolonged host contact; soft ticks (family Argasidae) lack a scutum and feed rapidly in sheltered microhabitats.

Etymology

Middle English tek, tike, perhaps from Old English ticia or related to Dutch teek, German Zecke.

Example

Ixodes scapularis, the blacklegged tick, transmits the Lyme disease spirochete Borrelia burgdorferi to humans during its nymphal and adult blood meals.

Synonyms

• Ixodida

Related Terms

• Ixodidae
• Argasidae
• Acari
• Parasitiformes
• hematophagy
• vector
• Engorgement
• Capitulum
• scutum

Usage Notes

In strict taxonomy, 'tick' refers specifically to the order Ixodida, excluding the numerous non-parasitic mites also within Parasitiformes. In medical and veterinary contexts, 'tick' often implies disease-vector species, though most tick species are not known to transmit pathogens. The common distinction between 'hard ticks' (Ixodidae) and 'soft ticks' (Argasidae) reflects both morphology and divergent feeding strategies, not phylogenetic proximity alone.