Thomas Morris

Tongue replacers, mind controllers, castrators and body morphs … no, this isn’t a new episode of Black Mirror, but the adaptations of parasites in the oceans.

We all have that housemate. When it’s your turn to cook, you know you need to cater an extra serving if you want lunch the next day, as this person will finish whatever is in the kitchen come dinner time. You pack a separate lunch box before you call everyone for dinner just so you know you’re covered. However, you wake up in the morning and that lunch box is in the sink, empty, with remnants of the meal on your housemate’s hoodie. Some say your friend is a ‘little eccentric’, but they are your friend, so you deal with it.

In 16th century Greece, there was a name for such a person: Parasitos - ‘person eating at another’s table’. It was a term used to describe a person who would come over for dinner, eat your food, drink your wine and only provide pleasant company as payment. They were also known to receive good hearted complaints for this strange adaptation and may go as far as to be considered the ‘jester’ of the party.

However, gaining food from unsuspecting hosts is anything but a strange adaptation. Since the 16th century, this word has morphed to explain one of the most successful lifestyles on this planet. Having evolved in practically every animal phylum, parasites rule the environment and utilize animals as their primary source of food, not caring for their host’s wellbeing. These cryptic animals are hyper adapted to their jobs and, in some cases, do some truly scary things in order to survive.

In the interest of Halloween this week, let’s take a look at some of the more creepy adaptations that these truly fascinating survivors have evolved

To start, let’s look at the ‘tongue replacer’ parasite. This isopod swims around till it finds a suitable fish host. It moves into the mouth of the fish, attaches to the tongue and starts feeding off the blood. Eventually the tongue dies and is lost, with the parasite replacing the function of the tongue. These parasites can cause serious damage to their host, mostly in the form of tissue damage, anaemia, stunted growth, and in severe cases death.

Parasites are known to go to extremes in body simplification, and no parasite has gone through as drastic a morph as the Sacculina parasite. This barnacle shows absolutely no resemblance to its hard shelled brothers and sisters attached to rocks, boats and ships. This soft bodied animal attaches to the underside of crabs, extending filament like tentacles into the cavity of the host, wrapping them around organs and feeding off its host directly. In the process, the parasite prevents the crab from moulting and being able to reproduce. All energy the host has that would normally go toward its own reproduction, is directed to the parasite, even changing the behaviour of the crab host to assist in the parasite’s reproduction.

Finally, and this is a good one, an internal parasite of class Trematoda that infects the digestive tracts of shore birds. In its life cycle, the parasite needs to go through two intermediate hosts to get to the shorebird, its final host. It does this by infecting a snail and then a small fish. When in the snail, it does the same thing as the Sacculina parasite, castrating the snail and utilizing this energy to feed and reproduce itself, releasing millions of larvae into the water. When the larvae find a fish host, they move into the brain of the fish, causing it to swim closer to the surface. It also causes the fish to behave erratically, causing it to shimmy and jerk, making it easier for the bird predator to snap them up, completing the life cycle of the parasite.

Maybe some great inspiration for those Halloween costumes, or just some creepy stories when sitting around the dinner table with that Parasitos of a housemate. Perhaps this will get them to respect the lunch box.

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