Parasites like this leech can be found all over the world, and anyone growing up near freshwater knows to check for them. But many consider these animals “gross”, so how can we motivate the public and scientists to care about them? (Image credit: John Douglas, CC BY-SA 2.0, Image Cropped)

As someone who works with parasites, I have to confess that I love them. They are beyond interesting, and I delight in telling people about them and what they do to their host organisms to survive. More often than not, people cringe or look like they would rather run away than hear more about such disgusting creatures. I know that as a disease ecologist I am very much in the minority when it comes to how I feel about parasites, but I think it’s important that we understand how vital these organisms are to the natural world, and the benefits they offer to scientists and their research.

I Walk Beside You

Parasites are one of the most successful life forms on this planet, infecting everything from microscopic bacteria to enormous whales. They are everywhere, and almost everybody in the world will have had one at some point. How many ticks do you think you’ve had in your lifetime? Mosquito bites? Leeches? Maybe even a tapeworm? So why don’t more people talk about them more, and why should we?

Why Avoid Parasites?

I think this question answers itself: parasites are by and large nasty to think about (and even harder to look at). These are organisms whose entire existence is dependent on sucking the life out of another organism, and this often involves some method of attachment to the host organism (lampreys, leeches, ticks, etc.) or even living inside of the host organisms (SO. MANY. WORMS.). Humans are prone to anthropogenizing the natural world, projecting our own feelings and thoughts onto the animals we are looking at. We see an eagle soaring through the sky (how majestic!), a pack of wolves working as a team to take down a much larger elk (how intelligent!), and then we see a young bird infested with nest fly larvae (how disgusting!!!). As Lara has pointed out before, humans care about pretty animals with faces. Parasites certainly aren’t pretty, and most people would struggle to find the face of a tapeworm (to be fair, they don’t really have one).

Why We Should Care

First and foremost, every organism on Earth is vulnerable to parasites. I’ll say that again: EVERY. SINGLE. ORGANISM. Even parasites sometimes have parasites (hyperparasites, check ‘em out). Not paying attention to parasites simply isn’t an option, it’s something that we as humans live with, and understanding the patterns and history behind these amazing organisms is imperative for the betterment of ecology.

Parasites, because they depend on host organisms to survive, offer one of the best natural systems in which to study coevolution. Hosts adapt to defend themselves from parasites, and unless the parasites can track these changes and overcome them, they die off. Because of this intimate relationship between hosts and parasites, we can use a host-parasite system to ask an incredibly diverse set of questions about evolution, ecology, disease dynamics, and food webs.

For example, did you know that there has been a rise in schistosomiasis in the areas around Lake Malawi in Africa because of a food web collapse? As human populations have grown and technology has improved, the lake has become increasingly overfished. Due to this, fishers have started illegally fishing in the shallower water where these fish normally eat snails. Because the fish (predators) are being removed from the population, the snails (prey) are much more numerous than before. These snails act as intermediate hosts for the schistosomiasis endoparasites, and they shed infectious flatworms into the water. Because people in this area use the water to wash, they come into contact with the flatworms and are infected.

Many parasites, like schistosomiasis, are complex and depend on more than one host to reach their final stage. Because they need to be able to adapt to and track more than one species, these parasites have to coevolve with multiple species all at the same time! This insanely complex coevolution has resulted in some fascinating adaptations to increase their success of transmission from one stage to the next (for a review of this see “Taken For a Ride”). In brief, parasites in the intermediate host are able to manipulate the host in such a way that the host dies, via suicide or predation. The parasite will then be inside of their final host aka the predator that ate their previous host.

Tropical mockingbird chick infested with nest flies (Philornis trinitensis). Case in point as to why many people don’t want to talk about parasites: THEY ARE GROSS. (Image credit: Jordan Herman, CC BY-SA 4.0)

The Benefits of Parasite Science

One issue that scientists struggle with is having large enough samples sizes to answer a particular question, and having the right study system can make or break an experiment. Because many parasites tend to be small it is relatively easy to collect and work with large numbers of them. For example, some of my colleagues work with birds and snakes (aka animals with spines) and they have to fill out mountains of paperwork verifying that they are treating the animals humanely, and even then they can only have dozens to (maybe) a couple hundred. Meanwhile, I go out in the field and in a single season I can collect THOUSANDS of parasites to use in my research, all with minimal paperwork. Additionally, many parasites (and plenty of host organisms) have very short generation times, so I can perform evolutionary experiments with multiple generations in the course of a year or two. Good luck doing that with a charismatic elephant (which have generation times of at least 15 years).

The complex dynamics that make up the lives of parasites have always been there, and it is something that we as scientists and as people in general need to make a better effort to understand. They may not be charismatic, they may be hard to look at, and they may even be deadly (looking at you, brain-eating amoeba…) but they are there and will likely ALWAYS be there. In addition to the ubiquity of parasites, we can also consider their practicality. They are easier to work with than charismatic organisms, can be used to answer endless scientific questions, and to put it simply they’re super cool (can a panda turn another animal into a zombie?). So settle in, prepare yourself, and get ready to welcome parasites into your life.