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Native plants are not always best for native insects

Wildlife of a garden,Jennifer Owen. Image ©RHS Native plants are not always best for native insects, non-natives also have an important role. That’s the message following a thirty year study in a British garden. For thirty years award-winning ecologist Dr Jennifer Owen studied, identified – and counted! – the insects and other creatures that visited her suburban garden in the English Midlands. And detailed it all in her invaluable book Wildlife of A Garden (Available in North America, and available in Britain) published by the Royal Horticultural Society.

She grew well over 400 different plant species - garden plants and weeds, natives and non-natives - in her garden (below, click to enlarge) which measures just 741square meters (8000 square feet). And she counted 23 species of butterflies, 375 species of moths, 94 species of hoverflies, 121 species of bees and wasps, 305 species of bugs, sawflies, lacewings and related creatures; 21 species of beetles, 122 species of other insects including two ants – all in her suburban garden. And 138 other invertebrates. And 57 birds and six mammals. Wildlife of a garden,Jennifer Owen,garden,Leicester. Image ©RHS

And as well as counting with extraordinary determination and great skill at identifying this vast variety of creatures – she also studied their food plants. And what did she find?

Dr Owens found that non-native species were better as food plants for moth larvae than native species. Moth larvae used 27% of the native species in the garden as food plants, and 35% of the alien plants. And 46 species of moth fed on 40 native plants in the garden, while 75 alien plants provided food for 38 species of moth.

She also looked at the four moth species with the most varied diets and the plants they ate. One ate 78% non-native plants, one ate 83% non-native plants, one 62% and one 79% non-native plants. They definitely didn’t favor natives. Of course, we don’t know how much of each plant each moth actually ate – after all, Dr Owen needs to get a few hours sleep each night.

And finally, what were the most popular food plants for moths? Plants in the rose family come out top, with seven native species and five non-native species used by 27 species of moth. And one of those native species, Potentilla fruticosa, is so rare in Britain it might almost be non-native. Next comes the Buddleja family represented only by the Chinese Buddleja davidii and used by 19 species of moth. The daisy family, the largest family of garden plants, hosts just 13 moth species all of which feed on aliens and only two of which feed on natives. And just to be clear: these are all British native moth species.

Wildlife of a garden,Jennifer Owen,tortoiseshell,aster. Image ©RHS You get the picture. I could go on, but this is just a blog post of a few hundred words. Read the book. OK then, one more thing. Dr Owen reports that of the 15 most widely used food plants in the garden nine are non-natives and only six are native. And some people think that introduced plants have no native larvae feeding on them at all!

This really throws the “natives are best” notion out of the window. We may like to think that natives are best, but they’re just not. And can’t we trust the insects know what they like to eat – wherever the plants come from? So why don’t we plant what the larvae actually like to eat, instead of what we think they ought to like?

This is an extraordinary piece of research summarized in a very readable and well illustrated book.

In my next post here, I’ll be looking at which buddlejas are best for adult butterflies. Because now we know.

           

 

* This post was originally headlined: "Alien plants are better for insects than natives – it’s official!" But after reflecting on the comments below, I modified it and substituted a less sensationalist headline. I also modified the introduction.

* At present, for some reason, amazon.com and amazon.co.uk don't seem to realize they have the books in their own warehouses and are not listing them as being available. They are available for shipping anywhere in the world from The Royal Horticultural Society.

Comments

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Graham Rice

Vincent, Genevieve. I really appreciate your thoughtful input.

I've looked at it again - and, on reflection, I think you're right. The headline was unnecessarily sensational in its language and while it clearly caught people's attention it wasn't the most constructive way to introduce what I believe is important research.

So I've changed both the headline and the introduction to the piece. I've also also added a note at the end explaining what I've done.

Thank you for taking the time to persuade me.

Genevieve

Graham, I admire you for taking a more reflective tone with your post and trying to be more accurate. The new title and intro helped me to read your post and subsequent comments with a more open mind, and I'm fascinated by this research. I hope that more scientists will study these complex relationships between plants.

I know as a landscaper it is extremely hard to create artistic places using a limited palette of primarily natives, much as I do love the regional flair they bring, so any deeper study of this topic would be enormously beneficial to people like us who make a career out of dealing with plants in some way. Thanks for bringing this to our attention.

Carole Sevilla Brown

I'm with Genevieve and Vincent. A general statement that says "Insects Prefer Exotic Plants" when it pertains to generalist insects is not the whole truth. As a Wildlife Gardener I do advocate the planting of more native plants in our landscapes because proportionally there are very few native plants in our gardens. Many people across the country are discovering the fact that increasing the proportion of native plants in their gardens means that they are seeing more wildlife species in their gardens. Since so many species of wildlife are threatened by habitat loss, it only makes sense to create welcoming habitat for them in our gardens. Otherwise, the only species we'll be left with are these generalist species.

Also, Doug Tallamy has responded to this research. You can see his thoughts here: http://nativeplantwildlifegarden.com/315/insects-prefer-exotic-plants.html

UrsulaV

Um. I'm an artist, math is absolutely not my strong suit, but no matter how I slice it, I'm getting 46 moths on 40 native plants, and 38 moths on 75 non-native plants, and I can't make that parse to anything but slightly more moths on a whole lot less native plants.

Was there a typo somewhere in those numbers?

Peter Scholtens

I haven't read Owen's book, but I wonder if, when she refers to moths using plants, she means adults using them as sources for nectar.

Tallamy's main point is that native plants have a far higher number of relationships within the ecosystems where they are found. Most of these relationships are different species of insects that feed on native plants as larvae. This makes native plants crucial in passing the sun's energy up into the rest of the biological pyramid. This process is something non-natives are not near as effective at doing because they do not have the same number of relationships.

Tallamy goes on to argue that this makes native plants crucial to breeding birds. Breeding birds need high protein diets to feed their young. A landscape with few native plants, such as most urban and suburban environments around the world, becomes a functional wasteland for breeding birds because they cannot find insect larvae to feed their young.

Graham Rice

Dr Owen's book is full of records of her counts, I really recommend reading it and thinking about her full argument. And she's definitely taking about larvae.

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