Day 1. It's alive; or is it?

Is a Parasite Alive? - Cian

Parasites are indeed alive! There are many different kinds. Some live inside a body, gaining entry when the host consumes contaminated water or food, or by digging their way through tissue. These are called endoparasites, and will survive by feeding off whatever the host itself or, the case of tapeworms, the food the host eats.

For all parasites, the host is the parasite’s meal ticket, but by stealing nutrition, destroying important tissues, and introducing toxins, the parasite can put both the host and itself in danger. Sometimes the parasite will end up killing the host and itself, but most often parasites cause damage but not death.  

Ectoparasites live outside the host. Leeches, fleas, and ticks are all examples of these nuisances. These parasites will survive by attaching themselves to the host’s body and find nourishment by eating skin or blood. The parasites themselves are usually not too dangerous or damaging, but the bacteria and viruses they carry can be deadly. 

But not all parasites are tiny bug-like creatures! Did you know that cuckoo birds are considered a parasite? They are known as a brood parasite, and will take advantage of another species of bird by laying their egg in another bird’s nest.

The baby cuckoo bird is clearly another species, but the warbler feeds it dutifully. Photo credit: Per Harald Olsen via Wikimedia commons.

The unsuspecting bird will care for the egg, along with its own eggs. The cuckoo bird egg generally hatches first, which is when the true nature of its parasitism shows. The baby cuckoo bird will often roll all the unhatched eggs out of the nest, killing off any of its competition. Yikes! If it fails to roll them out, it will outcompete the other hatchlings for food, growing at a much quicker rate.

One final parasite too cool not to mention is Cymothoa exigua, or the tongue-eating louse. This isopod starts life as a male living in fish gills. Once large enough, it becomes female and enters the fish's mouth where it carefully severs the blood vessels to the tongue. 

This causes the tongue to turn necrotic and fall off - but it's all part of the small crustacean's plan because now it can occupy that valuable real estate, which comes with a fabulous view and all the mucous and food bits an isopod could want. 

Near as we can tell, the fish doesn't seem to mind. The isopod attaches its hind legs to the tongue stump behaves as a semi-functional tongue for the rest of the fish's life. 

Three clownfish whose tongues have been replaced by the isopod C. exigua. The white head and eyes are visible peaking out from the fish's mouths. This photo by Quin Lin won a wildlife photographer of the year award in 2017.

Happily, C. exigua can't parasitize mammals. Your own tongue is safe! But for red snapper and a wide number of other ocean fish -- they might well end up with a tongue that has a mind (and eyes) of its own.

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