Ticks and Diseases

Tick Life Cycle

Ticks have four life stages: egg, six-legged larva, eight-legged nymph and eight-legged adult. The "hard ticks" (the group that most commonly attack people) feed once during each stage. 

Egg to Larvae

Eggs are fertilized in the fall and deposited in leaf litter the following spring. They emerge as larvae in late summer of that year, seeking their first blood meal. The tiny larva crawls around the forest floor and onto low-lying vegetation looking for an appropriate host. Their first host is generally a mouse or other medium sized mammal or bird. Once attached, the larvae embed their mouth parts and feed for several days. If the host is infected with a disease such as Lyme, the tick may be infected during this feeding. The larvae then drop off their host into the leaf litter where they molt into the next stage, the nymph, remaining dormant until the following spring.

Larvae to Nymph

During the spring and early summer of the next year the nymphs end their dormancy and begin to seek a host. Nymphs are commonly found on the forest floor in leaf litter and on low lying vegetation. Their host primarily consists of mice and other rodents, deer, birds and unfortunately humans. Most cases of Lyme disease are reported from May through August, which corresponds to the peak activity period for nymphs. This suggests that the majority of Lyme disease cases are transmitted by nymphal Blacklegged (Deer) Ticks. After feeding for several days the nymph ticks drop off to the forest floor.

Nymph to Adult

Over the next few months the nymph molts into the larger adult tick, which emerges in fall, with a peak in October through November. Both male and female adults find and feed on a host, then the females lay eggs sometime after feeding.
 
Adult ticks wait for host animals from the tips of grasses and shrubs approximately one meter above the ground. When an animal or person brushes by the vegetation, they quickly let go and climb onto the host. Adult ticks feed on their host for five to seven days. The female will become engorged with blood, providing nourishment for her developing eggs. After feeding and mating, the female tick drops into the leaf litter where she lays thousands of eggs. She will become dormant as the temperature drops below 40° F.

Tick Facts

Ticks can only crawl; they cannot fly or jump. Ticks found on the scalp have usually crawled there from lower parts of the body. Some species of ticks will crawl several feet toward a host. Ticks can be active on winter days when the ground temperatures are above 45 degrees Fahrenheit.
 
There are two groups of ticks, sometimes called “hard” ticks and “soft” ticks. Hard ticks, like the common dog tick and blacklegged (Deer) tick, have a hard shield just behind the mouthparts (sometimes incorrectly called the “head”); unfed hard ticks are shaped like a flat seed. Soft ticks do not have the hard shield and they are shaped like a large raisin. Soft ticks prefer to feed on birds or bats and are seldom encountered unless these animals are nesting or roosting in an occupied building.
 
The most commonly encountered ticks are the American dog tick, lone star tick, blacklegged (deer) tick and brown dog tick.  

Tick Biology

Source: Richard Ostfeld, Ph.D., Dutchess County Department of Health, National Institute of Health, Illinois Dept. of Public Health.