Every other Friday on Morning Edition, Outside/In host Sam Evans-Brown tackles a question from a listener.
Cindy from Chichester asks: "Every year I have a skunk that comes around and makes divots all over my yard looking for grubs. The question is this: Do they actually know that there is a grub in the place that they dig, or do they just randomly dig holes until they find something? I have not been able to get an answer to this question, so it’s your turn."
Challenge accepted, Cindy.
Cindy is not wrong in pointing out that there are not a huge number of skunk experts out in the world, who are not “pest control professionals” and therefore perhaps not terribly interested in the finer points of skunk behavior.
Now — if you’ll allow me a brief tangent to rant about how our personal biases skew the accumulation of scientific knowledge — this is part of a pattern. Generally speaking, biology as a field has a bias towards the rare, the unusual and the charismatic. The common, the mundane, the everyday are often largely ignored.
But fortunately for Cindy, skunks fall into a liminal space: while they are quite common, they are also considered a pest — another category of species we devote a lot of attentiong to. As such there is skunk research out there. So, I did find a skunk expert, Dr. Ted Stankowich, who introduced himself as someone who does research on “the evolution of armor and weaponry in mammals,” which is pretty awesome.
(Unfortunately, the gentleman that several people have pointed to as the nation’s preeminent skunk evangelist, the delightfully named Jerry Dragoo, did not get back to me. But his website, in all its late 90s formatting glory, is worth the click.)
Wow, that was a long tangent.
Ok! To Cindy’s question!
Ted says skunks have terrible vision and very good noses. As such, they use their nose to decide where to dig. But do they get a grub every time? That is a question we could design a study to answer, but no one has. “Whether or not they actually find anything underground is really hard to tell unless you’re actually watching them up close with a scope or binoculars and seeing if they’re actually chewing after they dig up a hole,” explains Ted.
But is it reasonable to think they might be able to smell grubs through the soil? Rick says skunks sense of smell is roughly as good as that of dogs. And if you think that some dogs can smell underground mushrooms that are worth $2,000 a pound, or perhaps even smell diseases like cancer, it’s not unreasonable to think skunks only dig when they smell a grub and are not just randomly creating chaos in your yard.
Back to the evolution of weapons and armor
Okay, now that I’ve got you here thinking about skunks, can I take this opportunity to pose a question?
This defense that skunks have evolved is obviously really really useful. Most predators learn very quickly to leave them alone, and owls are apparently the one species that attacks them with any regularity. So if being able to spray horrible smelling goo is such an advantage, why haven’t more species evolved the ability?
Stankowich has found that defenses like skunk spray or porcupine quills or armadillo armor are much more likely in medium-sized mammals that live in open habitats.
“If you’re too big to hide naturally in your environment, and you’re too small to size out of being killed by all the carnivores around you, then you’re in this perfect size range to be a tasty morsel,” he says. “And if you add on top of that, living in an open environment like a grassland or a desert these animals are going to be much more at risk of being seen by predators and they’re living a much more dangerous lifestyle.”
All of that exerts powerful evolutionary pressure to develop a stinky spray.
Sam Evans-Brown, is host of NHPR’s Outside/In which you can subscribe to where-ever you get your podcasts. If you’d like to submit a question you can record it as a voice memo on your smartphone and send it to firstname.lastname@example.org, OR call the hotline, 1-844-GO-OTTER, OR submit it here.