This is on point. I'm Megna Chacrobardi. What do you think of when I say the word

parasite? I'm betting it's maybe something slimy or gross. Well, there are a lot

of different kinds of parasites out there and parasite ecologists Chelsea

Wood spends a lot of time looking at them and studying them and she joins us

today. Chelsea, what do you think of when you think of parasites? The word

parasite evokes for me this beautiful, netherworld of organisms that most

people are unfamiliar with that exists just under the surface of everything

that's familiar and that are beautiful. They play by their own rules. They do

things that are out of a sci-fi movie and yet they're more common than pretty

much any other organisms that surround us. Wow. Well, Chelsea Wood is an associate

professor in the School of Aquatic and Fishery Sciences at the University of

Washington and Professor Wood does study parasites. So I'm delighted to have you

today because in a sense the fact that parasites occupy this netherworld as you

talk about means that we need to pay more attention to them. So first of all,

let's start with some of the basics. When we see parasites, how should we define

them? What part of the kingdom of life are we talking about? Let's a special

thing about parasites. It's a term that describes a group of consumers a way of

living. So it's not necessarily about one particular branch of the tree of life

but about a lifestyle that's evolved many, many times all across the tree of

life. I define parasites as organisms that live in or on a host and cause that

host of fitness costs. Basically, they take energy from their host and that means

that the term parasite encompasses everything from viruses and bacteria to

...