Flatworms are generally unseen, un-celebrated critters. But there are more than 20,000 species of them and they are found just about everywhere there’s water. However, they can be hard to find because much of their life cycle is spent inside a host organism. That’s the yuck-factor (think tape-worm). Still, they are pretty fascinating.

The whoa-factor about flatworms was described to me by a young friend who shares my love of the natural world, especially the weirdly wonderful aspects of it. One evening this summer as we marveled at fireflies, she told me that most flatworms only have one opening in their body. Wait, what? It is true. These simple organisms only have a mouth. They eat with that mouth. Then their food moves through the simple digestive system. So…what happens to the stuff that isn’t digested? Well, it has to come out the mouth. Back to yuck. Other materials are also excreted through special cells called flame cells. Tapeworms, by the way, do not have a digestive system at all – they simply absorb the nutrients they need from their host.

Another interesting aspect of flatworms? Some species are actually quite pretty. Nonetheless, I think I still rather not be a host.