Even unpopular parasites are sometimes important to ecosystems, and global warming is wiping them out.

Parasites are a tough sell, and it’s easy to understand why. An eclectic mix of specimens from the Smithsonian’s parasite collection. Credits: Paul Fetters for the Smithsonian Institution/Courtesy of Science Advances

Parasites such as lice, ticks, and fleas are disliked for good reasons — they can sting or bite you and sometimes carry nasty diseases, but they often serve important roles in ecosystems. A new study found that as climate change kicks in more and more, up to a third of all these parasites could be wiped off, with dramatic consequences for everybody.

The evil you know

The first concern is that as some parasites are killed off, their place will be taken by others, and this will almost certainly lead to invasions from the surviving ones. They also keep other creatures in check and fill in some very important links in the food chain. If they go away, other creatures which dine on these parasites will be left without their favorite food and this can propagate on the food chain, much like a domino effect.

In order to reach this conclusion, researchers across eight countries spent years pinpointing the habitats, needs, and current environmental situation of 457 parasite species. They also analyzed the collection of 20 million parasites held at the Smithsonian Institution’s Museum of National History in the US to map their distribution.

Our action (or lack of action) will have a huge impact on the planet’s wildlife — including ecosystems. Different scenarios will carry different outcomes. Image via Wikipedia.

They came up with startling numbers — depending on the future climate scenarios, between 20% and 37% of all parasites will meet their end, making them one of the most threatened groups on the planet.

“It is a staggering number,” said Colin Carlson at the University of California, Berkeley, who led the new work. “Parasites seem like one of the most threatened groups on Earth.”

Ignored

Because of their bad reputation, parasites are massively understudied. No one wants to fund research, no one really wants to dedicate their career towards studying them, and people overall just don’t like them. Especially in relation to climate change, we don’t really know what the impact on parasites would be, and this is shaping up to be a massive problem.

“Parasites are obviously a hard sell,” said Carlson. “Even if you are grossed out by them – and there are obviously downsides for individual hosts and for humans – parasites play a huge role in ecosystems.”

But they do provide up to 80% of the food web in many ecosystems, and having a wide range of parasites means they compete with one another and keep each other in check.

“If parasites go extinct, we are looking at a potential massive destabilisation of ecosystems [which] could have huge unexpected consequences,” Carlson said, with other parasites moving in to take advantage. “That doesn’t necessarily work out well for anyone, wildlife or humans.”

This is just one of the first studies to focus on this aspect; 457 species is not that much, and we’re just getting a glimpse into what is certainly a complex puzzle. Hopefully, things will change in the future.

The bottom line is even if we don’t like them, understanding parasites is almost certainly useful.

“It is difficult to summarise the net consequence, as we know so little about most parasites,” Carlson said. “Climate change will make some parasites extinct and make some do better. But we would argue the overall phenomenon is dangerous, because extinctions and invasions go hand in hand.”

Journal Reference: Colin J. Carlson et al. Parasite biodiversity faces extinction and redistribution in a changing climate. DOI: 10.1126/sciadv.1602422