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Photo of Mark Siddall.
Photo by AMNH/D. Finnin

The Leech Guy

Mark Siddall takes an interest in creatures most of us avoid: leeches

Mark Siddall (BSc 1988 St. Michael’s, MSc 1991, PhD 1994) is a molecular evolutionary biology and biodiversity specialist at the American Museum of Natural History in New York who takes a passionate interest in creatures most of us strive to avoid: leeches. Here, he tells Janet Rowe about coming to grips with these unappreciated little suckers.

Why leeches? Were all the cute critters taken?
No, few had bothered with these cute critters yet!

So… you wade through the Amazon barefoot…?
It’s fieldwork in remote places, yes. But actually, the job is not just about discovering species. It used to happen a lot that several different people would find something and describe a new species and it turns out it’s the same one, and now it’s got three names. Sorting that out is also part of the job, and this is why natural history museums are important. They are libraries of biodiversity.

Why is it important to study even unloved animals, such as leeches, and promote biodiversity?
Because we don’t want to live in a world that’s just full of pandas and pine trees. That’s boring. And quite frankly, the movement towards any and all research having to be directed toward some sort of economic goal, I think is – can I use the word asinine? If discovery is no longer interesting, we should just go home and watch reality television.

Why are people scared of leeches?
It’s learned. If someone screams “Oh my God, you’ve got a leech on you,” you automatically have negative thoughts associated with it. My daughter has grown up with leeches and she thinks they’re awesome.

So tell me some awesome stuff about leeches.
They’re incredibly beautiful swimmers, they have gorgeous colour patterns. Their ability to detect movement from huge distances is really quite powerful. And when they’re feeding, their whole body goes limp. It’s like they’re paralyzed.

I don’t know! I’ve asked them and they don’t answer.

What else is awesome about leeches?
How much time have you got? The leeches that I worked on in my master’s and my PhD, when they produce their young, they’ll stay with those eggs, and they’ll fan the eggs, until the eggs hatch. And then the young will attach to the underside of the parent, the young then get taken to their first blood meal. So there’s parental care!

Are leeches still used medicinally? There are some legitimate uses for them that have to do with removing blood congestion, usually from things like reattached fingers, ears. The purpose is really to remove blood that’s accumulating in an area to give veins the time to regrow back into the tissue. It works! Your other options are to stick the area with needles over and over again for seven days. No fun and painful. Leeches, not so painful.

Why does salt work, to get leeches off?
You’re basically dehydrating the leech. It’s a very bad idea, though.

For the leech?
For you. The research we’ve done has demonstrated that leeches have bacteria that live in their gut. If you salt the leech, in addition to the unhappy eventuality that you’ve just poured salt into a wound, it could cause the leech to regurgitate into the wound and establish an infection. Just let them finish, or push their face – at the skinny end – to the side and then peel off the sucker at the fat end.

When you name a leech species, do you name it after your enemies?
I don’t have any enemies! I’ve named one after my daughter, Ali, because she found it: Placobdella ali. Then there’s Tyrannobdella rex; we named it so we could say that T. rex was alive and well, feeding on children in the Amazon.

Your thoughts on U of T?
I’ve obviously really enjoyed my time at U of T, so much so that I did all three degrees there and it doesn’t seem to have harmed my career at all.

Watch Mark Siddall hunt leeches in Rwanda in 2009, and explain their fascinating medicinal uses:

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