From his office in the American Museum of Natural History in New York, Mark Siddall looks out over Central Park, sylvan home to two favorite creatures:
Somewhere deep in the lakes and ponds below, Erpobdella punctata and Helobdella robusta are awaiting spring.
Siddall is the world’s leading leech expert and the curator of “Life at the Limits,” a new show at the museum that presents animals that have adapted in unusual ways to places humans would find very stressful.
Unsurprisingly, the exhibition includes a leech plucked from a very deep Croatian cave. But it has competition from such extraordinary creatures as the noble elephant seal and the microscopic, shape-changing tardigrade, the show’s mascot.
In the dimming afternoon light, Siddall’s specimen jars took on an eerie glow.
We sat down near the imposing Haemopis grandis, which dines on earthworms. Not all leeches feast on blood.
Hoelterhoff: Generally speaking, what are leeches good for? I associate them with the dark days of medicine.
Siddall: Interestingly, the use of leeches was not as medieval as people think. Medieval bloodletting was fairly medieval. You would actually slice veins open -- let people bleed.
Leeches were really popularized in the 1800s by a French surgeon in Napoleon’s army named Broussais.
He associated all diseases with inflammation of the gastrointestinal tract. Broussais used about a half a million leeches in one hospital in one year. Some 54 million leeches were exported from France in a single year in the mid-1800s!
Hoelterhoff: That’s a lot of leeches.
Siddall: They were almost extirpated. In “Resolution and Independence” by William Wordsworth, an old man wanders over the moors lamenting the fact that he can’t find leeches.
Hoelterhoff: What did he do with them?
Siddall: Sold them. Leeches were for everything: Obesity through hysteria, melancholia. Someone even wrote a treatise on the use of leeches to treat nostalgia.
Hoelterhoff: Leeches seem to have made a comeback.
Siddal: In flap and reimplantation surgery you need a way to drain the blood. You could use a cannula, a straw-like thing, but that opens you up to infection and injury.
Hoelterhoff: So the leeches suck the excess blood.
Siddall: And keep the pressure down as the arteries are feeding the tissue and that will give time for the veins to grow back. So you can reattach a finger say. The process is also used in breast reconstruction after cancer, which I think is terrific.
Hoelterhoff: Any other uses? Didn’t Demi Moore’s beauty routine include leech therapy?
Sidall: She went to a spa in Austria and had leeches feed around her belly button to take the bad blood and leave the good blood? Does that happen? No!
There’s a difference between using leeches in a proper medical environment and using them in a spa.
Leeches have microbes -- they have bacteria that live inside them that if they regurgitate into the wound could give you cellulitis.
There’s even a case of meningitis. Some of them are antibiotic resistant. In a spa, it’s a real risk.
Hoelterhoff: Are there some leeches you like more than others?
Siddall: That’s kind of like asking which one is your favorite child.
Hoelterhoff: What’s the biggest leech you’ve ever seen?
Siddall: The giant Amazonian leech that can grow as big as your forearm.
Hoelterhoff: And that’s still a leech?
Siddall: They feed on anacondas.
Hoelterhoff: Can’t the anaconda eat them?
Siddall: It’s hard. The anaconda can’t bend everywhere. And they eat things much bigger than that.
Hoelterhoff: I wonder what they taste like, say stir-fried. Any idea?
Siddall: I don’t believe there are any people who eat leeches. Leeches are not particularly abundant. Caterpillars are much more abundant. Ants are more abundant. Termites are more abundant. Crickets are more abundant. I’ve eaten a lot of bugs.
Hoelterhoff: Do leeches show much action when they’re alive?
Siddall: Yes, yes, yes. Some have what’s called a looping gait when they’re moving on a solid surface. They use their front sucker and their back sucker to accomplish that.
The medicinal leeches can swim. And they swim in a highly coordinated fashion. The European medicinal leech swims in a perfect sine wave. The North American medicinal leech swims in a sine wave and a half.
Croatian Cave Dwellers
Hoelterhoff: Show-off leeches. Was it tough to decide which leeches to include in your show? I noticed the Croatian cave leech got in.
Siddall: The cave leech was an obvious choice because there is no other leech on the planet that we know of that has appendages that appear to be very clearly an adaptation to feeling around in a cave a kilometer and a half down.
Hoelterhoff: What’s the biggest discovery you made while preparing this show?
Siddall: In terms of personal discovery, I would have to go with the European kestrel, which is a bird of prey, which feeds on small mammals like voles. It follows their pee trail which happens to fluoresce in ultraviolet. Kestrels can see in ultraviolet. That’s awesome.
Hoelterhoff: How will climate change affect the creatures in your show?
Siddall: Life will continue to exist on this planet. That’s not what’s at stake with climate change. The real issue is will there be any people around to witness it.
This interview was adapted from a longer conversation.
Manuela Hoelterhoff is executive editor for Global Cities at Bloomberg.