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Canyon Creek Schoolhouse Laboratory 100th Anniversary

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Life cycle of ticks

Studying the life cycle of ticks provided important pieces of the RMSF puzzle. Knowing the life cycle meant that scientists could study questions such as: When did the ticks pick up the bacteria causing RMSF—was it when they were newly hatched? When they were adults? And was the infection passed on to a new generation of ticks through the eggs? The answers to these questions could be used in control efforts and in developing a new vaccine.

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Tick with eggs bunched together in bundle larger than tickImage Modified

The life cycle of the tick: a fertilized female lays thousands of eggs on the ground. When they hatch as larvae, they attach to small animals and feed. Then they drop off to digest their meal, and molt (shed their old shell) to become nymphs. The first winter they spend as unfed nymphs.

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Female and Male ticks on white background

In spring, the nymphs once again attach to an animal and feed, drop to the ground, and digest their meals. This time they molt to adults, like these Rocky Mountain wood ticks, Dermacentor andersoni. They spend their second winter as unfed adults.


Close up of ticks on grass stalks in meadow

The next spring they climb grass and bushes to attach to animals.


Engorged tick swollen many times its normal size

But as adults, ticks mate as well as feed. This is when the ticks can get the Rickettsia rickettsii bacteria from the animals they feed on. Even though the bacteria don’t hurt the ticks, it infects all of their cells, and is passed on through the egg. The next generation of ticks will be infected.

Images: Office of NIH History and Stetten Museum, 1554-58

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