What is a parasite, anyway? “A parasite is an organism that spends a significant portion of its life in or on the living tissue of a host organism and which causes harm to the host without immediately killing it.” (Source: parasitology.com) Parasites have evolved highly specialized adaptations allowing them to exploit their hosts, including some incredibly complex life cycles. “Parasitoids” tend to kill their hosts (but in nature things get complicated…)

We still know very little about the vast majority of parasites compared to other organisms. Why do you think this is true?

?v=vMG-LWyNcAs An (actual) example of a parasitoid (a species of ichneumon wasp) and its charming approach to reproduction. It’s an obligate parasitoid, meaning it needs its host organism to survive. Note the dramatic life cycle transitions…

“Every living thing has at least one parasite that lives inside or on it. Many, like leopard frogs and humans, have many more. There’s a parrot in Mexico that has thirty different species of mites on its feathers alone. And the parasites themselves have parasites, and some of those parasites have parasites of their own… Scientists have no idea just how many species of parasites there are, but they do know one dazzling thing: parasites make up the majority of species on Earth. According to one estimate, parasites may outnumber free-living species four to one. In other words, the study of life is, for the most part, parasitology.” - Carl Zimmer, Parasite Rex

Microparasites Viruses and Bacteria Protozoa (Eukaryotic critters) Macroparasites Animals (especially invertebrates) Fungi Plants

Giardia Plasmodium (causes malaria)

Plasmodium life cycle

Hookworms Roundworms Ascaris, the human roundworm, affects as many as 1 billion people worldwide

Flukes Tapeworms

Bed Bugs Fleas Head Lice

Ticks Demodex – “Eyelash mites”

the “Fish Tongue- Depressor” isopod

Tarantula Hawk Wasp

Indian Pipe

Cuckoos & Brown-headed cowbirds Obligate nest parasites

Not only do many parasites have incredibly complex life cycles (with multiple distinct stages that move between different host organisms); some can even alter their host’s behavior in bizarrely specific ways (i.e. creepy zombified mind-control…) From Snail to Bird Cordyceps fungi Liver flukes: from Ant to Cow

What role(s) might a parasite play in a food chain? What kinds of impacts might parasites have on an ecosystem? How might they contribute to an ecosystem’s health? How might they cause it to become unstable? Parasite Ecology

Parasites, in addition to causing major human human health issues, are incredibly weird, complex and fascinating. Like it or not, they are a fundamental part of life on Earth. We are only beginning to learn just how diverse parasites really are and to understand the many important ecological roles they play in nature. Looking at historical (and modern day) attitudes towards parasites can teach us lessons about human bias and subjectivity in the process of science.