Climate change could make flea collars obsolete.

A mass extinction of fleas, ticks and roundworms and other parasites might sound like a good idea to pet owners, but it could have devastating consequences for the Earth.

It could happen. And as soon as 2070, according to a new international study of 457 parasitic species, published this month in the journal Science Advances. Seventeen researchers from eight countries spent years tracking down different parasite specimens in order to understand the species’ habitat and needs.They found that one-third of all parasites are endangered by habitat loss due to climate change. And it’s possible that some parasites may be in greater danger than their hosts.

Parasites may have a bad reputation, but researchers say a mass extinction could accelerate the spread of diseases and enable the hardier parasites that do survive to proliferate. The parasites included in the study are diverse group. They include tapeworms, roundworms, ticks, fleas, lice, and other organisms generally considered to be pests best known for causing disease in humans, livestock, and other animals, including household pets. Their negative image is easy to understand—parasites, by definition, live and thrive at the expense of a host.

But at the same time, parasites play important roles in complex ecosystems. Among other benefits, they help control wildlife populations and keep energy flowing through food chains. Many parasites have complicated life cycles that require them to pass from one host to another.

Which means, perhaps paradoxically, that a strong parasite population often indicates a healthy ecosystem.

And there such things as good parasites. We just don’t tend to think of them as parasites. Some you can eat, like fungi, which include mushrooms. Then there’s yeast, which is used to make bread and beverages. Some parasites, like leeches and maggots, are used in medicine. Grown in special laboratories, they can be used to keep blood flowing or to clean up dead tissue when treating people after accidents. 

The study points out that if parasites face a high risk of extinction due to climate change, the cascading impact on ecosystems could be profound. Many parasites play an important role in regulating the immune systems of their hosts, and a higher diversity of parasites can act as a partial buffer against the invasion of a virulent pathogen.

One thing is certain. A mass extinction due to climate change won’t necessarily favor good parasites over bad parasites. They’re all at risk.

“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,” said Colin Carlson from the University of California Berkeley, lead author of the study.