If you haven't been traumatized today, then you've come to the right place. Here you can meet members of the phylum Nematomorpha, creepy worm parasites that leave their victims scarred both physically and emotionally. Also known as horsehair worms, these disgusting parasitoid animals can be found in nearly every corner of the globe terrorizing their hosts and sucking the life right out of them. Many horsehair worms can even grow to be as heavy as the hosts they inhabit. Highly invasive, these creatures can take over a host's bodily functions, even going as far as rewiring their victims' brains.
Parasitic horsehair worms primarily target invertebrates like insects but scientists believe that the worms are increasingly becoming a concern for humans as well. Studies documenting the risk of horsehair worms infecting humans have been published recently and the results are more than a little disconcerting.
If we're going to make sure that a horrifying epidemic of mind-controlling worms doesn't take over humanity, we're going to have to get to know our enemy a little better.
Horsehair worms have a complicated and unsettling life cycle that plays out like a rejected movie script from the Alien franchise. Each one starts off as an egg, just one of 15 million laid by the mother. Once hatched, getting eaten becomes a worm's top priority so that they can start their parasitic life.
Some species choose hosts that are likely to become food for even larger insects, allowing them to infect the largest possible host.
A critical part of every horsehair worm's life is their eventual emergence from the host body but they can't emerge just anywhere. Because these worms are aquatic animals and need water to lay their eggs, they've developed an adaptation that allows them to take over their host's mind. It might sound like science fiction, but horsehair worms essentially "zombify" their hosts and force them to seek out water. Creatures that struggle to survive underwater will willingly throw themselves into the nearest creek, pond, or puddle at the command of the parasite.
The worms achieve this mind control effect by pumping brain-altering chemicals known as neurotransmitters into their victim.
It's almost impossible to tell on sight whether an animal or insect is playing host to a horsehair worm... unless the animal gets close to water. Then the animal will almost cannonball into the water source, prompted by the parasites that have infected its brain.
The survival rate of hosts often depends on whether they can swim or not: After dispensing their worms they're left on their own.