Ticks are small arachnid parasites that feed on the blood of animals and humans. This article explores their ancient history, global spread, and how they find hosts.
The Ancient Origins of Ticks
Ticks are not insects, but rather arachnids, placing them in the same class as spiders and mites. Their bodies are typically unsegmented. Ticks share a common ancestry with mites, and some genomic studies suggest they form a single evolutionary lineage with mites, making them a diverse group of chelicerates.
The fossil record indicates that ticks have an ancient lineage, with their earliest known fossils dating back approximately 100 million years to the Cretaceous period. These early ticks likely fed on slow-moving, smooth-skinned reptiles and amphibians. Molecular data suggests the last common ancestor of all living ticks may have existed even earlier, around 195 million years ago, in the Southern Hemisphere landmass known as Gondwana.
From Ancient Past to Global Presence
From their ancient origins, ticks diversified and spread across the globe. The breakup of the supercontinent Gondwana played a role in their early dispersal. Ticks adapted to various environments, evolving into the two major families recognized today: hard ticks (Ixodidae) and soft ticks (Argasidae). Hard ticks are characterized by a scutum, or hard shield, which soft ticks lack.
The global distribution of ticks has been influenced by climate changes and the migration patterns of their host animals. Ticks are primarily dispersed by their hosts, as they cannot fly or move long distances independently. Birds and mammals, including deer, have been significant in transporting ticks to new regions. This host-mediated dispersal has been a primary mechanism for their spread and the establishment of new tick populations.
How Ticks Find Their Way To Us
Ticks are commonly found outdoors, favoring wooded areas, tall grasses, and leaf litter. They thrive in warm, humid locations with low-lying vegetation. Ticks do not fly or jump; instead, they employ “questing” to find a host.
During questing, a tick climbs onto vegetation and extends its front legs, waiting for a host to brush by. When an animal or human makes contact, the tick quickly grabs on. Ticks detect potential hosts through sensory cues, including breath, body odors, carbon dioxide, body heat, and vibrations. They can also sense lactic acid. Once attached, some ticks may wander on the host’s body to find a suitable feeding spot, often preferring concealed or thin-skinned areas like the armpits, groin, or scalp.