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Thursday, June 1, 2023

Column: World’s scariest parasites

Every now and then, I like to take a break from looking at the beauty of nature to look at the weirder, more terrifying things. For all the beautiful creativity that nature shows in the world around us, a close look can also find creatures that we find horrifying.

The most likely kind of creature to inspire this feeling is the parasite. A parasite is any organism that lives at the expense of another organism. Within that huge definition are two categories: endoparasites and ectoparasites. Endoparasites are parasites that live inside of the cells of host organisms, such as viruses and some species of bacteria. Ectoparasites, by contrast, are parasites that live outside of the host organisms, such as ticks.

These definitions are all well and good, but let’s see some real life examples of parasites.

Common Cuckoo: At their worst times, perhaps after weeks of little sleep, a parent may be forgiven for wanting someone else to take care of their children, at least for a while. For humans, that’s what grandparents or aunts and uncles are for.

Cuckoos, a species of small bird, take this wish quite a few steps further. Cuckoos will take their eggs to the nest of another bird species, push the other bird’s eggs out of the nest and replace them with cuckoo eggs. When the other bird returns to the nest, they take care of the baby cuckoos while some or all of their own eggs have vanished.

There’s a connection here to the old legends of fairies taking human babies and replacing them with fairy look-alike children for the human mother to take care of.

Leucochloridium: Leucochloridium is a genus of flatworm that matures in the intestines of songbirds. Well, that’s no fun for the songbird, but how is that any different from the myriad of parasites that infect animals in a similar way?

The Leucochloridium has to take an indirect and strange path to get to the intestine of the songbird. The worm lays its eggs in the intestine, which the songbird then passes out in its feces. A snail then makes its way to the feces and eats. The worm eggs are now inside the snail; they hatch, and now must get back into the songbird. However, songbirds don’t eat snails. How do they get there?

The answer is amazingly creative, though disturbing. The parasite forces its way into the snail’s eyestalks and begins pulsating. The eyestalk becomes enlarged from the parasite and makes the snail want to crawl toward sunlight. The songbird, thinking the snail’s eyestalks are a different creature it would like to eat, snatches the eyestalks.

Point: leucochloridium.

Slave-Driving Ant: Common names of animals are very helpful for understanding certain characteristics of the animal. The most obvious is the slave-driving ant. The slave-driving ants, officially called Anergates, invade the nests of Tetramorium and steal their pupae. When they hatch, the slave-driving ants make the Tetramorium ants work for them. Anergates do not make workers of their own and cannot even feed themselves without the slaves.

Unequal Conjoined Twin: In contrast to slave-driving ants, the official name of conjoined twins is much more informative than the common name of Siamese twins. For reasons not completely understood, most likely incomplete splitting of a fertilized egg, causes two individuals to share one or more organs. They could be attached at the hips, head or any other variety of locations.

An unequal conjoined twin, also called a parasitic twin, is when one twin is stronger and healthier than the other. The stronger twin eventually takes all of the nutrition from the other twin, resulting in the eventual death of the weaker one.

Why is this creepy? If you were one of the unequal conjoined twins, you were the strong one that absorbed the other. Think of the episode of “The Simpsons” in which Bart discovers that he had an evil twin, only to discover at the end of the episode (spoiler alert) that he had been the evil twin all along. Obviously, there’s no real good-evil binary in this situation; the stronger twin isn’t trying to cause harm, it’s just trying to survive.

Why do parasites act in the way that they do? While it is tempting to assign the parasite an “evil” role, that’s not really telling the full story. Take the cuckoo; the only reason the adult cuckoo knows which bird species to invade is because it remembers what species raised it as a hatchling.

While these are interesting cases, and fun to assign them horror movie plot-lines, keep in mind these organisms are only trying to do the same thing that we are — to survive.

AMY STEWART can be reached at science@theaggie.org.