Awesome Animal - Hammerhead Worm

Due to the Halloween season, I'm going with a rather creepy-themed Awesome Animal today. I present to you the hammerhead worm—the coolest worm most people have never heard of.

There's even a species with Halloween colors (see image below).

Honestly, I didn't know anything about these until recently, and I immediately decided I needed to feature them as an Awesome Animal.

What the heck is a Hammerhead Worm?

Actually, these are not worms like earthworms. Earthworms are segmented worms. Hammerhead worms, on the other hand, are planarians, a type of flatworm. Sometimes they are called broadhead planarians. Another common name--landchovy.

Most species of planarians live in freshwater or saltwater, but some types, like the hammerhead worms, live on land.

Perhaps the most distinguishing characteristic is the broad, shovel-shaped head.

Land planarians have what's called a creeping sole that allows them to move around. This creeping sole is on their ventral (belly) side, and it has a thick layer of cilia (moving, hairlike projections) that beat back and forth on a strip of mucus the worm lays down as it progresses forward.

What, you didn't expect these things to produce copious amounts of slime?

To top it all off, these worms are fierce predators, as well as cannibalistic. Oh, and they are invading North America, Europe, and many other parts of the world.

And... if you cut them into pieces, you end up with more hammerhead worms.

Oh... and some of them grow to 18 inches (half a meter) long.

Amazing Facts about Hammerhead Worms

Wait... what was that statement about cutting them up and ending up with more? Planarians are famously good at regeneration. You can literally slice one in half, either lengthwise or across its body, and in two to three weeks each half will grow a new planarian. If you cut one into five pieces, you might get five worms (this depends on several things, including how big the pieces are).

In fact, this splitting is the main way most hammerhead worms reproduce. Yeah, they are capable of sexual reproduction—you know, with a male and female—BUT, hammerhead worms are hermaphroditic, which means each individual has both male and female sexual organs. Therefore, any individual can mate with any other individual. Strangely, though, they usually don't. Instead, they seem to prefer to make new hammerhead worms by splitting their body apart. This is known as fragmentation and is a handy form of asexual reproduction.

How do they split themselves apart? Well, they stick the tail end part of their body to the ground (remember all that slimy mucus?), then they keep moving forward (remember that creeping sole?) until their body tears right in half. The broken piece they leave behind becomes a younger worm, growing longer and developing a broad hammer head in a few weeks. A hammerhead worm can break apart like this one or two times per month.

Lifespan of a hammerhead worm: Potentially immortal.

I know, that's weird, but get this—hammerhead worms have no respiratory system, no circulatory system, no skeleton, and their mouth is also their anus.

Let's consider those one at a time.

No respiratory system: There's no need. Oxygen enters and carbon dioxide leaves the worm's body by diffusing directly through the body wall.

No circulatory system: There's no need, for the exact same reason as above.

Mouth is also the anus: Now we're talking about the digestive system. It's a simple system. The mouth is located in the center of the ventral (belly) side. Food is taken in there and travels through a pharynx to a gastrovascular cavity, where it is digested, and because this cavity branches out to various parts of the body, that's how the nutrients get everywhere they need to be. Whatever is left over gets spit right back out the mouth. Nice.

Let's talk about how these creatures eat. As I stated above, they are predators. Unfortunately, many of them kill and eat earthworms. In case you didn't know, when it comes to almost every aspect of an ecosystem, earthworms are the good guys. gardeners know you can't have healthy soil without earthworms. That's why invading hammerhead worms could be bad news.

Hammerhead worms are vicious earthworm hunters. They glide around on the ground with their spade-like head held up, moving it back and forth like a radar. The broad head has special chemoreceptors that detect earthworm mucus. When they catch up to one, they subdue it with a coat of their own mucus (wow, there's a lot of mucus in this newsletter), then they tear it up into pieces. The hammerhead worm then extends its pharynx out of its mouth and secretes earthworm-dissolving enzymes all over the chopped-up prey. After the earthworm becomes soup, the predator sucks it all up, digests most of it, and spits the remains back out the mouth.

These creatures are an earthworm's worst nightmare (although it seems unlikely earthworms have nightmares—they have very primitive brains).

Hammerhead worms are also enthusiastically cannibalistic. They like eating each other.

Hammerhead worms are native to Asia and Australasia. However, as I stated above, they are becoming invasive worldwide, probably due to being transported on horticultural plants.

Possible solution: Maybe predators (or even people) could eat them. Nope. Many earthworms are edible, but these creatures are toxic. They contain a potent neurotoxin called tetrodotoxin, which is also found in some newts, pufferfish, and the blue-ringed octopus. Other than each other, they have few predators.

If you pick them up, their surface mucus can cause skin irritation. And, of course, don't even try chopping them up.

I know... I'm kind of making these creatures out to be overly creepy for this Halloween edition. But keep in mind that in their native habitats, hammerhead worms are important to the ecosystem and should not be killed. They are, after all, awesome animals.

When it comes to invasive hammerhead worms, they could become a problem. If you see an invasive hammerhead worm, you can pick it up with gloves or tweezers and put it in alcohol, or salt, or a sealed container. It might also help to report it to local authorities, who might be tracking sightings in your area.


So, the Hammerhead Worm deserves a place in the E.A.H.O.F.
(Elegant Animal Hall of Fame).

FUN FACT: The word elegant (meaning "tastefully ornate") originated in the late 1400s, and it came from the Old French élégant. Another definition, one that I think applies to the appearance of some of the hammerhead worms, is "graceful in form or movement." Yet another definition is "excellent; fine; superior," as in "This is an elegant wine." I suppose you could consider hammerhead worms to be nothing more than slimy, slug-like things, but you have to admit they have a rather delicate and graceful appearance, right?
So, elegant is another way to say awesome!

Photo Credits:
- Hammerhead worm from Borneo, orange, black, and white - DepositPhotos
- Hammerhead worm, black and white - DepositPhotos
- Hammerhead worm, black and orange #2 - Bernard DUPONT, Flickr, Creative Commons License (CC BY-SA 2.0)
- Hammerhead worm, long, thin, black - "Hammerhead worm - Carita - West Java_IMG_2708" by fveronesi1 is licensed under CC BY-SA 2.0
- Hammerhead worm head, brown and white - DepositPhotos