• Andy Davis

Food for thought - should monarchs be squished in countries where they don't belong?

Hello blog readers,

Whoa, right? Let me quickly ask you about your knee-jerk reaction to this blog title - did you read that and immediately feel horrified? Revolted? A sense of uneasiness? Like how could anyone think of squishing a beautiful monarch? Please do keep reading, because in today's blog I want to unpack why you feel this way, and hopefully, impart a little lesson or two in the process. Today I'll be talking about the issue of native and non-native species, as it relates to monarchs (yes, even monarchs can be non-native).

Let me first do a small sidebar here to add some context. The reason I'm bringing this topic up is because in the last year I've been deeply involved in some other research involving a non-native species to the United States, and so I guess this subject has been on my mind a lot. For those who don't know, I also study a variety of other critters in my lab, including a new one, which is not native to Georgia - the joro spider, Trichnephila clavata, which is from east Asia! You may have even seen some recent news about a new study about them. There were articles in just about every major newspaper, television and online organization in the U.S. and Canada. You can google this spider (or even just use my name) and literally find hundreds of articles by now. Below is a picture of this critter from the New York Times.

Anyway, I guess this media frenzy experience is still fresh in my mind. One thing that struck me about all of the articles, and the feedback from viewers, readers, etc., is that the vast majority of people out there apparently have no problem with squishing these (beautiful) non-native spiders. In fact, some people even considered this their duty, because that spider does not belong here. One person wrote a comment that they have squished hundreds of these spiders in their yard in the past couple of years. Do you see where I'm going with this? To such people, this spider represents a "threat" to the native fauna, or, that they are competing with the native spiders. Technically, these folks probably are not wrong. It's true that these spider are probably competing with native spiders for food. But on the other hand, these joro spiders could also become food for our native birds, or wasps. In fact, research from a colleague of mine here at the University of Georgia has shown that a lot of non-native species often become food for natives, given enough time.

Let's now talk about another non-native species that monarch folks are more familiar with - oleander aphids - and this is another good example of a species that brings about a lot of opinions. These are those tiny yellow bugs that sometimes cover milkweed plants. This species is not native to the U.S. or Canada, but it has successfully colonized both countries. To some people, these are a pest, because they are "eating" the milkweeds that had been planted for monarchs (technically, they don't eat the plant, but suck the juices of it). And once again, I have seen many comments by people who think this species deserves to be squished, because it doesn't belong here, or it is invasive, or whatever (exactly the sentiment about the spider). But one thing that never gets mentioned when people are ranting about these, is that as with the spider, these aphids do serve a beneficial role now, by becoming hosts to native Lysiphlebus testaceipes wasps, who use them to reproduce. And, there are even native ants that use these aphids to get honeydew. So in other words, even though they are indeed non-native, they are at least providing a benefit to some native species.

So, this brings me to the monarchs. I've pointed out in prior blogs that we now know that the "ancestral" monarch population (i.e. the first one) is the one in North America, and that all of the other subpopulations around the world are basically offshoots. This is another way to say that the monarch is not native to these other places. There are monarch populations in Australia, New Zealand, Spain, the Caribbean, Hawaii, Bermuda, and others. We actually don't know if monarchs arrived at these places on their own steam, or if they were transported by humans, but in the end it doesn't change the fact they they don't belong there.

This is a map from the monarch Wikipedia page, showing all of the places where they can be found around the world. I see that someone has also added dates to the map, which (I think) indicate the approximate timeline for when the monarchs arrived at these places.

So in these other countries, monarchs do what monarchs do - they lay eggs on milkweed plants and the caterpillars eat the plants. But, here is the rub - there are native insects in these places that need those milkweeds for their life cycles too. So in other words, monarch caterpillars are freeloaders in these countries, eating plants that mother nature had intended for the natives there. So...does that mean the monarch caterpillars deserve to be squished in these countries? See, this idea goes both ways. If non-native insects and spiders in North America should be squished, then why shouldn't non-native monarchs in other countries?

I bet I've got you thinking now! I can guess too that some readers may be thinking that maybe the non-native monarchs are providing a service in these places, by pollinating the native plants, at least. Wrong. It turns out that monarchs are really crummy pollinators in general. In fact they don't even pollinate milkweeds! Think about it - when is the last time you saw a monarch covered in pollen? So really, this is no justification for not squishing them.

I should make it clear that I am actually not advocating for doing this, since this blog post is more of a thought exercise, and where I am trying to get readers to question why they feel a certain way about things.

When it comes right down to it, I think the real reason people would feel horrified about squishing monarchs is simply because they find them pretty, or because of a variety of other "emotional" reasons - not because of any science. In fact, this same emotional issue also works in reverse toward the spiders - people "feel" negative emotions about the spiders, and so therefore have no compunction about squishing them. What really is the difference between these two species - is one good and the other bad?

Here is an example of how things can get dicey when we allow our emotions to rule our decisions about nature. In New Zealand right now, people are actively engaged in helping the monarch population there (where it is not native). Based on what I've read, people there are doing what everyone in North America does - buying milkweeds, planting gardens, etc., to help monarchs. But at the same time, the OE parasite levels in that country are rising - see a prior blog. And, we now know that this parasite can affect other Lepidopteran species - see another prior blog. So, what if the OE parasite starts killing off the native species in that country, all because people are trying to "help" monarchs (which are not supposed to be there)? We don't have any research on this yet, but this is something that I could easily see transpiring. Does this justify helping the monarchs there?

I guess the take-home message from this whole "thought exercise" is that we shouldn't be making decisions about matters related to the natural world based solely on emotions, or human attachments. Rather, we should be using evidence and science. And, if there is no research on a topic, then we should rectify that!

I hope this post made you think.



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The science of monarch butterflies

A blog about monarchs, written by a monarch scientist, for people who love monarchs