Parasitism’s Charisma Deficit

The medicinal leech, Hirudo medicinalis, is one of the few parasites formally protected. Photograph: Stephen Dalton/Alamy

By the time I was welcoming guests to a place where they would experience them in the wild, I had become accustomed to leeches. I did not enjoy feeling them in my hiking boot or elsewhere on my body, but after a few times I stopped being freaked out by it. As unlikely as it sounds, I eventually found them fascinating, if not charismatic. I could appreciate their place in the ecosystem we were working to protect, but I could not bring myself to celebrate them in public. A photograph like the one above would not win them new friends but illustrations like the one below might help. Phoebe Weston’s article about the challenges of protecting parasites rings true:

Overlooked and unloved: how a global project could unlock the world of parasites

The tiny freeloaders may be considered disgusting by many but new research shows they are crucial in shaping ecosystems

A coloured aquatint from the early 19th century shows three women gathering leeches in a stream. Photograph: Wellcome Collection

The leech craze of the 1800s put parasites on the map. Collectors (usually women and sometimes old horses) would stand in ponds waiting for medicinal leeches to come and suck their blood. They were then picked off and sold for bloodletting.

The parasites were so popular that by the early 1900s they were nearly extinct, and there was a coordinated effort to save them. Even so, the European medicinal leech, Hirudo medicinalishas been labelled as near threatened on the IUCN red list since 1996, and remains one of the few parasites with formal protections.

Only 4% of known parasites infect humans but it is no surprise that these freeloaders are not in favour. Conservation funding tends to follow charismatic creatures, and ticks, tapeworms and fleas are not good PR for parasitism. Malaria, which is caused by a bite from a mosquito infected by the plasmodium parasite, killed an estimated 408,000 people in 2018.

“It’s not the sort of thing WWF or Conservation International is going to be doing work on,” says Colin Carlson, a biologist at Georgetown University in the US who has just published a paper in the journal Proceedings of the Royal Society B arguing for a global parasite project to record parasitic life on Earth.

Parasitism refers to a type of ecology – or lifestyle – where a living thing feeds off a host. Because parasites hide in hosts, they are difficult to study (often you do not know they are there) so it was assumed they were not that important and probably did not have much impact on overall food chains. More recent research has shown that this assumption is wrong, as parasites significantly alter food chains.

Increasingly, scientists are finding that parasites are puppet masters, shaping ecosystems by changing the behaviour of their host species. Research in California showed parasites were involved in 78% of links in the food chain. Rough estimates suggest there could be 80 million parasites, but only 10% have been identified…

Read the whole story here.

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