Photos: Wildlife-Friendly Garden and signage, © S Heard CC BY 4.0. Monarch caterpillars on milkweed (in Minnesota), Courtney Celley/USFWS, CC BY 2.0.
My university, like many, is concerned with appearing green, and among its projects is a series of small plantings that offer (mostly) native plants with educational signage. I pass by one of these every day on my walk to work: the “Wildlife-Friendly Garden”. It has Joe Pye weed, roses, goldenrod, and a few other things, and it has some signs introducing passers-by to its “frequent visitors”.
One of the “frequent visitors”, we’re told, is the monarch butterfly: it has a lovely and informative sign. This seems unremarkable: everyone loves monarch butterflies, everyone knows they’re common visitors to late-summer flowers like goldenrod and Joe Pye, and everyone knows they’re a species at risk* worth cherishing. So how could I possibly have a beef with this sign? Well, here’s the thing: my university is in Fredericton, New Brunswick – and we don’t have monarchs here. Or almost not.
Monarch butterflies, of course, are milkweed specialists as larvae (photo above the post). Common milkweed, Asclepias syriaca, reaches its northern range limit very close to Fredericton (and in fact, its occurrence here probably represents a fairly recent range expansion as a result of habitat alteration by humans). Unsurprisingly, where milkweed comes to a range margin, so does the monarch butterfly (and the rest of the specialist milkweed-feeding fauna too). In Fredericton, I see on average one adult monarch butterfly a year. I’ve never seen a caterpillar here, suggesting that our occasional adults are probably storm-blown or otherwise casual visitors. We aren’t terribly far from places with more monarchs – there’s a long-running study tagging migrating monarchs about an hour’s drive south – but the near-absence of local monarchs is nonetheless consistent.
And yet: the “frequent visitor” sign for monarchs is no outlier. Our local newspaper regularly prints exhortations to plant milkweed for monarchs; elementary schools plant and celebrate these milkweed gardens, and rear and release monarchs from farmed pupae; and I frequently hear members of the public talking about monarchs as if they were common members of our local fauna. In fact, I’d wager that people “remember” seeing monarchs in their gardens, despite the fact that such sightings are almost certainly imaginary. This is a fascinating failure of observation. Monarchs are common in public discourse and in people’s media experience, and so people just assume they’re common in their direct experience too – even if they aren’t.
This has always bugged me about monarchs. But I make the same failures of observation myself; and I bet you do too.
I was thinking about this after getting reviews back on a recent manuscript. One reviewer suggested that we were remiss in not citing the extensive literature that establishes point X. I was actually quite pleased to get this criticism, because point X really would have been stronger with citation. So off I went down an internet rabbithole searching for that literature. Guess what? No such thing. And I could be annoyed by this, but I know that more than a few times, I’ve been on the other end of this exchange. Usually, it’s when I suggest to one of my grad students that some point in their paper merits a citation, and I say “there are lots of papers about this”. And sometimes I’m right – but sometimes, I’m very, very wrong.
There are things we all know, and we presume that the reason we know them is that we’ve read papers saying so. As scientists, that’s generally how we know things, right? But sometimes, these things we know turn out to be just things we think we know. As a concrete example, I’ve been told a million times that insect herbivores can reduce performance of individual plants, but don’t impact plant population dynamics. I’ve lost track of the times someone has told me about the literature that supports this contention. The thing is, it doesn’t exist. Everyone thinks they’ve read papers demonstrating that herbivores don’t influence plant populations, but those papers are as imaginary as the Fredericton monarchs. In reality, nobody studies the question because we all think we know the answer; but we don’t know the answer because nobody studies the question**.
Failures of observation: imaginary monarchs, imaginary papers. We let things everyone says and everyone takes to be true override our own (lack of) observation. It’s a funny failing for scientists, who are supposed to favour evidence above all else. But then, scientists are just people, and when we aren’t deliberately vigilant, we do what people do. It will be good for me to think about this each time I pass the monarch-less Wildlife-Friendly Garden.
© Stephen Heard November 28, 2017
*^Largely due to issues with their overwintering range in Mexico, not with the availability of larval and adult resources in their summer range, but that’s another story.