Brainworm Life Cycle

Say hello to Parelaphostrongylus tenuis

If you thought your life was complicated, it pales in comparison to the lifecycle of the microscopic nematode formally known as Parelaphostrongylus tenuis, but usually called by its common name of brainworm or meningeal worm.  In order to reproduce, all you have to do is find someone of the same species but of the opposite sex.  The brainworm nematode needs to find not only another brainworm nematode, but a deer and a snail or slug.

The Worms and the Eggs

Adult brainworms live in the meniges of one specific deer species, the white-tailed deer.  The meninges are the tissues in between the brain and the skull, but brainworms have also been found in the meninges tissues around the spinal cord.  Amazingly, these worms do no damage to this specific species of deer. 

The adults then mate and release eggs in the tissues surrounding the spinal cord.  The larvae hatch in the nice warm environment and then wriggle down to the lungs.  It is vitally important that the larvae get into the deer’s mouth.  The quickest way that happens is for the deer to cough.  After coughing the larvae into its mouth, the deer swallows the larvae. 

The Significance of Deer Feces

The deer’s digestive system does not digest the brainworm larvae.  They pass right on through inside of the deer feces.  The larvae stay inside of the deer feces.  Why?  Because deer feces are the favored food of many types of slugs and snails.  The slugs and snails eat the deer poop and inadvertently eat the brainworm larvae.

The larvae then feed inside of the bodies of the snails and slugs. Sometimes these snails and slugs are eaten by other snails and slugs.  The nemtodes can survive even this digestive process.  By this time, the larvae are now adults.  Snails and slugs not only like to eat deer poop but plants that are often eaten by white-tailed deer, especially white-tailed deer that live in or around swamps.  While grazing or browsing, white-tailed deer often accidentally eat snails and slugs along with their more conventional diet of plant matter.  

The adult brainworms travel into the digestive system and enter the bloodstream and then use that to travel to the meinges, where its time to start the cycle again. 

Are Brainworms Found in Other Species?

Unfortunately, many other creatures eat the same foods as white-tailed deer, even snails and slugs.  These creatures include black-tailed deer, elk, moose, caribou, reindeer, llamas, goats, sheep and very rarely and often under laboratory conditions, guinea pigs.  But the brainworm is not in the one deer host it needs to survive.  Stranded in the wrong body, it not only dies, but often takes the host animal with it.


Michigan Department of Natural Resources and Environment. “Brainworm.”,1607,7-153-10370_12150_12220-26502-,00.html

Fairfax County Public Schools. “Brainworm Nematode.”

Michigan State University. “Meningeal Worms (Brain Worm) and Liver Flukes (Deer Flukes): Two Uncommon Internal Parasites.”

“Parelaphostrongylus (Brainworm) Infection in Deer and Elk.” Corry Jeanne Mortensen BSc, BEd & Murray Woodbury DVM, MSc.