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Understanding the Ecology of Tick-Borne Disease

The natural process that leads to tick-borne disease involves deer ticks (the black-legged tick)—how they eat and how they reproduce. For ticks to survive, they need plenty of blood to feed on and a place to mate. During their quest for these two things, they can infect humans and animals with the bacteria that causes tick-borne disease.

The Life of a Deer Tick

The life span of a tick is 2–3 years.

First year

● Previously mated female ticks deposit eggs in late May–early June and die.● Larvae hatch from the eggs in August. They are not infected with the bacteria that causes Lyme disease, anaplasmosis, or babesiosis.● During the fall they feed mostly on small mammals—mice, chipmunks, squirrels, voles, or shrews. Some of the small mammals carry the tick-borne disease bacteria, and they infect the larvae.● Larvae over-winter under leaf litter.

Second year

● In the spring larvae molt into nymphs. They are the size of a poppy seed.● In June and July the nymphs feed on small mammals, birds, deer, people, dogs, and horses. Nymphs that have molted from larvae infected with disease-causing bacteria will infect the new year's crop of small mammals, which, in turn, will infect the next generation of larvae.● In August–September most nymphs molt into male or female adults. A few will delay molting until the next year.● In October–November females feed primarily on deer, but also on humans, dogs, cats, and horses.● Males do not feed, but collect primarily on deer to mate. After mating, the males die.● The females fall to the ground where they over-winter.

Third year

● Females that have fed and mated deposit about 3000 eggs in late May–early June and die.● The nymphs that did not feed at the end of the second year seek hosts from May through July. In September/October they molt into adults.

The Role of Deer

It is important to understand the role that deer play in a tick's life.

● Deer provide the two things that ticks need in order to survive—a place to mate and, for the females, blood that nourishes their egg production.● Although ticks will feed on medium or large-sized animals such as dogs, cats, foxes, horses, moose, and humans, research has shown that their strong preference is for deer.● Deer do not carry or transmit tick-borne disease bacteria. Their only role is to accommodate the ticks.● The size of the tick population in a given area is tied directly to the size of the deer population—the more deer there are, the more ticks there are.● According to scientific consensus, if a deer population is reduced to about 10 per square mile in a given area, adult ticks cannot find a blood meal and a place to mate. After a couple of years, the tick population is greatly reduced.