Secernenteans: Secernentea

Physical characteristics: Female canine heartworms are 10 to 12 inches (25 to 30 centimeters) long and about 0.2 inch (5 millimeters) wide. Males are about half the size of females.

Geographic range: Canine heartworms live all over the world. Because they are found throughout the world, no distribution map is provided.

Habitat: Canine heartworms live mainly in warm areas. The primary hosts, also called final hosts, are dogs, cats, ferrets, foxes, wolves, sea lions, and humans. In their hosts adult worms live in the right ventricle of the heart and the blood vessels that connect to it. The intermediate hosts are mosquitoes.

Diet: Canine heartworms feed on their hosts' nutrients, primarily through blood in and around the heart and lungs.

In their hosts adult canine heartworms live in the right ventricle of the heart and the blood vessels that connect to it. (Illustration by John Megahan. Reproduced by permission.)

Behavior and reproduction: Adult canine heartworms live in the pulmonary arteries of their primary hosts. The pulmonary (PULL-muh-NAIR-ee) arteries take blood from the heart to the lungs. Rather than releasing eggs, the females release large numbers of microscopic young worms—as many as five thousand a day—into the host's bloodstream. These microscopic worms can stay in the host for a year or more but cannot develop further until they enter a mosquito. A mosquito bites the host and sucks in the worms with the hosts' blood. The worms start maturing inside the mosquito, which bites another animal and injects the young worms into it. The worms travel to the heart, become adults, and start releasing microscopic young in the new host. Adults can live in a host and continue to produce microscopic young for several years.

Canine heartworms and people: Canine heartworms are dangerous to people and their animals.

Conservation status: Canine heartworms are not considered threatened or endangered. ∎