Why is a tick dry? - briefly
Ticks have a hardened, waxy cuticle that repels external moisture, giving them a dry appearance. They acquire water primarily from the blood of their hosts and ambient humidity, eliminating the need for a wet surface.
Why is a tick dry? - in detail
Ticks survive in environments where moisture is limited. Their exoskeleton is covered by a waxy cuticle that limits evaporation. The dorsal shield (scutum) is composed of rigid chitin, creating a barrier that reduces water loss through the integument. Spiracles, the openings for respiration, are equipped with valves that close when humidity drops, preventing desiccation.
Physiological mechanisms support dryness tolerance. Ticks store water in the hemolymph, where proteins such as hygroscopic trehalose bind moisture and maintain internal pressure. Malpighian tubules concentrate waste and reclaim water, limiting excretion. During periods without a host, metabolic activity declines, lowering respiratory water loss.
Behavioral strategies further protect against dehydration. Ticks position themselves in leaf litter or shaded microhabitats where relative humidity remains high. When questing, they extend forelegs only briefly, reducing exposure time. Some species ascend vegetation during humid mornings and retreat when conditions dry.
Life‑stage differences affect water requirements. Larvae and nymphs possess thinner cuticles and rely more on humid microclimates, while adult females develop a larger engorged abdomen after feeding, allowing them to store substantial fluid volumes for egg production.
Host attachment resolves dryness instantly. Blood ingestion supplies large quantities of water and solutes, replenishing hemolymph and rehydrating tissues. After feeding, ticks retreat to protected sites to digest the meal, during which they restore internal moisture balance.
In summary, the combination of a waterproof exoskeleton, regulated spiracles, osmotic control, reduced metabolism, and selective habitat use enables ticks to remain dry for extended periods until they locate a host.