Brainworm Nematode

Parelaphostrongylus tenuis


Oklahoma State University

The Brainworm Nematode is one of many species of nematodes. Nematodes, also called "roundworms," are a large group of tiny, microscopic worms. Nematodes are not related to earthworms or any other worms other than nematodes. Nematodes, even though they are tiny, have long skinny, hair-like bodies. They do not have segments like earthworms.

Nematodes live just about everywhere, even though you don't see them. They live in soil and in water. Some are parasites and live inside other animals. The Brainworm Nematode is one of these parasites.

The Brainworm Nematode has an interesting life cycle because it depends on other animals to live, especially snails, slugs, and White-tailed Deer. Here's how it works:

Adult brainworms live in the blood and tissue that covers the brain of a White-tailed Deer. Even though they live in such a sensitive place, they don't seem to cause the deer too many problems. Adult brainworms lay eggs near the brain, and the eggs are then carried through the deer's bloodstream to its lungs.

Inside the deer's lungs, the eggs now hatch into larvae (baby nematodes). The larvae begin a long journey from the lungs (the deer's breathing organs) up the trachea (the deer's windpipe). Once the larvae crawl out of the deer's trachea into its mouth, they then get swallowed and pass through the deer's stomach and out in the deer's poop.

Grossed out yet? We're just getting to the good part!


Roberta Stacy

Oklahoma State University

Now that the Brainworm Nematode larvae are outside the deer, they wait in the deer poop for their next ride.

Snails and slugs, such as the Eastern Forest Snail or the Leopard Slug, are plant-eaters. Sometimes they eat living plants (especially young ones), and sometimes they eat dead plant material, such as old leaves and stems. Since White-tailed Deer are also plant-eaters, they usually have bits of old plants in their poop. These bits are just the right size for a snail or slug to eat.

When a snail or slug eats the deer poop, they sometimes eat tiny nematode larvae. Now the larvae are inside the body of a new host (snail or slug). Sometimes a snail, such as the Eastern Forest Snail, is eaten by another snail, such as the Disc Cannibal Snail. If this happens, the larvae then enter a new host.

Inside their host, the nematode larvae continue to develop and grow. They have almost become adult nematodes, and they could not do this anywhere else except in snail or slug bodies. They do not seem to harm the snails or slugs either! In fact, the snails and slugs continue to crawl around looking for more plants to eat.

There is one more step in the life cycle of the Brainworm Nematode. They must find their way back inside a White-tailed Deer's body in order to finally become an adult nematode and lay new eggs. Fortunately for them, since snails, slugs, and deer eat mostly the same foods, they have a decent chance. A deer may come along and, while munching on plants, accidentally munch on a snail or slug or two. When this happens, the nematode larvae are back inside a deer.

Now all the larvae have to do is work their way through the deer's bloodstream back to the brain. There they can lay eggs and start the cycle all over again!

Copyright, University of Pennsylvania

Brainworm Nematodes cannot live without both the White-tailed Deer and their snail and slug hosts. They need to live inside each animal in order to develop and grow.

Nematodes also depend on the temperature. They need a warm evironment to grow. Therefore, in the Winter, when snails and slugs hibernate, the nematodes have to wait. In the heat of summer, the nematodes have to wait again, since many snails and slugs estivate (hide from the heat under dead leaves and logs so they don't dry out).

Ohio State University, College of Veterinary Medicine

The picture above shows some Brainworm Nematode eggs under a powerful microscope. There are eggs of other species in this picture as well. The brainworm eggs are the medium-sized, oval-shaped ones (Not the ones with the pointy ends).

Relationships in Nature:


Predatory Nematode

White-tailed Deer H


Eastern Forest Snail H

Leopard Slug H

Disc Cannibal Snail H

Relationship to Humans:

Brainworm Nematodes, for the most part, have little effect on people. They are not transferred from deer to people (although other dangerous nematodes are, so it is important to cook deer meat thoroughly).

Sometimes brainworms end up in grazing animals, such as goats or sheep. Since these are not deer, the nematodes get lost and end up in the wrong places. This can cause a goat to get sick and die.


Parelaphostrongylus tenuis


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