A Global Plan for Parasite Conservation

Why should we conserve parasites?

If you’re a long-time follower, you probably already know why we should conserve parasites. But for those of you who are new, welcome, and please enjoy this short journey into posts from the past!

Parasitism is a common consumer strategy in the natural world; so much so that 40-50% of all animals might be parasites! That’s perhaps millions of parasitic animal species spread across 15 phyla, including animals as diverse as ticks, intestinal worms, and bot flies. There are also parasitic plants and fungi. Parasites might have especially high extinction risks, because they are at risk from both primary extinction pressures, like the direct effects of climate change, and secondary extinction, or co-extinction, when their host species decline or disappear. If conservation efforts are supposed to conserve all species based on their intrinsic value, then parasite species should be a large target for conservation activities.

But maybe you’re more of a utilitarian, and you want to know what parasites do for ecosystems and for us. The short answer? A lot, and probably a lot more than we know. We know the most about parasite species that harm people, harm our domestic species, and threaten wildlife species, but those parasite species are just drop in the bucket of global parasite biodiversity. We haven’t discovered and described most of those other, relatively benign parasite species, even in groups that we know provide important ecosystem services, like the parasitoid wasps that provide pest control. And some parasite species have already gone extinct due to human activities—science didn’t even give them a name before we didn’t have them any moa. All of this is to say that we do not know everything about parasites, so we do not know exactly what a world without parasites would look like.

But we do know that parasites play important roles in ecosystems. For example, parasite biomass is a large and important part of food webs. Within food webs, parasites link many species together in ways that we might not even expect, like the nematomorphs that cause crickets to jump into streams, where the crickets are eaten by endangered Japanese trout. Every non-parasitic species that you can think of evolved with parasites and interacts with parasites, which is why sex and immune systems evolved. In humans, immune systems might totally freak out in the absence of parasites, leading to auto-immune disorders. While no one wants to conserve detrimental human parasites, a few relatively benign parasites might be good for people and other species, too. Parasites are so central to the biology and ecology of non-parasitic species that some question whether we can even conserve hosts without their parasites: if we brought back mammoths from extinction, but couldn’t bring back mammoth parasites, would we really have brought back mammoths?      

What steps do we need to take to conserve parasites?

There are strong arguments for conserving parasites, but unfortunately, we are not conserving parasites yet. In fact, in some cases, we are driving parasites to extinction when we try to conserve other species, like when we delouse or deworm host species brought into captivity. Given how little we know about most parasite species and how little we are currently doing to conserve them, what immediate steps can we take to conserve parasite biodiversity?

We suggest that 12 steps should be taken in the next decade to conserve parasite biodiversity. Some of these steps will appeal most to researchers interested in fundamental science and people who want to participate in community science programs, because they involve data collection and synthesis. For instance, we need more research about how parasite biodiversity responds to changes in host biodiversity. Other steps are geared more towards practitioners, because they involve risk assessment and prioritization and conservation practice, like creating ways to assess parasites’ extinction risks and building red lists of threatened parasite species. And everyone can enjoy and be involved with the steps related to education and outreach, like including parasite-themed lessons in K-12 and college education.

If you’re interested in learning more about the 12 steps in The Global Parasite Conservation Plan, check out our recently published paper! This was a wonderful group effort from an international team of researchers, many of whom you might have seen at our ESA Organized Oral Session in 2018. And for a bunch of new papers about parasite conservation, check out our whole “Parasite Conservation in a Changing World” special issue that was just published in Biological Conservation!

This was, of course, a shameless plug for my own research, but it was for a good cause. Let’s save the parasites.

50%-ish of life = Parasites

Ecologically Oriented very kindly linked to my blog today.  While I was over there visiting, I realized that I haven’t blogged about the ubiquity of parasites yet!  If I’m going to talk about parasite ecology, I should probably emphasize how common parasites are.  Though this is a topic that might well span multiple blog posts, a good starting point is this 2008 PNAS paper.  The paper is pretty much a gold mine of interesting tidbits, so I highly recommend reading it (the link is to the full-text).  Here are some of my favorite points:

Dobson et al. (2008) start the paper by pointing out that if you want to know the proportion of the world’s biodiversity that is parasitic, you probably need to know how many species there are in the world.  Unfortunately, we don’t know how many species there are.  A temporary answer is:  a lot, and a lot more than we have currently described.

There are estimates that something like 40-50% of organisms are parasites.  I don’t know what percentage of organisms are “predators,” or “prey,” or “predators AND prey” – is that review paper out there? – but 50% is probably comparable.  Parasitism is a common strategy!

Don’t forget that those 50% of organisms actually have to parasitize other organisms.  So, how many species are parasite hosts?  Well…all of them, probably.  Even parasites have their own (hyper)parasites!

I like this line from the Dobson et al. (2008) paper:  “In the best-studied taxa, an average mammalian host species appears to harbor two cestodes, two trematodes, and four nematodes, and an acanthocephalan is found in every fourth mammalian species examined.”  You’ve probably spent your life striving to do better than average, but maybe in this case you’ll settle for falling behind the curve?

So, pretty much every organism is either a parasite or has parasites or both.  That is a wonderful reason to frequently read a blog about parasite ecology!  😛  But why else should we care about parasites and parasite biodiversity loss?  Here are some reasons outlined by Dobson et al. (2008).  First, parasites are important in host population regulation.  Second, they’re important parts of food webs; I’ll blog about that separately in the future.  Third, helminth parasites bioaccumulate pollutants.  Again, that’s a story for another blog post, or you can check out the paper for more details.



Dobson, A., K.D. Lafferty, A. Kuris, R. Hechinger, and W. Jetz. 2008. Homage to Linnaeus: How many parasites?  How many hosts? PNAS 105(S1):11482-11489.