“The Insects Remember” or: why am I doing all this?

As gardeners and landscape designers, we grow native plants for a variety of reasons. For their beauty of course, but also because of an innate sense that we’re helping to make ecosystems whole again - having been so ravaged by human exploitation. And while it gives us a good feeling inside to install a new native bed, and to see insects flocking to its blossoms, I suspect that most of us also believe in our hearts that our work has a meaningful impact on the broader picture, if only on a tiny scale.

I’ve been reading the scientific literature on the subject, and in particular, on the impact of bringing locally native plants back to urban spaces, even very small ones. In my research, one ecological entomologist’s work has stood out to me, that of Professor Luis Mata, at the University of Melbourne. Professor Mata has done some lovely and rigorous work on the question: can small native planting interventions in urban spaces promote local wildlife diversity?

If you’re reading this, you probably assume that the answer is “of course,” but that’s why we do science, to challenge or support our hypotheses. Across multiple studies though, Dr. Mata’s work has consistently answered, “Yes.” We already know, in part thanks to the extensive work of Doug Tallamy at the University of Delaware, that insects can be hyper-specific about the plants that they use, whether for egg laying, nectar and pollen feeding, or a host of other behaviors. But does that mean that restoring those plants to degraded landscapes will necessarily bring the insects back?

That’s where the marvelous quote in the title of this post comes in: as Dr. Mata said on a great podcast episode, “The insects remember.” In the case of Melbourne, a recent study by his group showed that many insects native to the grasslands which Melbourne displaced, suddenly reappeared when their co-evolved plant community returned, even to tiny urban parks completely surrounded by cityscape. The insects remembered. Crucial to this approach is determining what was local and native before humans disrupted the landscape, precisely the type of data available in Barton, 1818, and that makes Philadelphia an excellent location in which to replicate this sort of study.

And crucially, the insects that returned were overwhelmingly those that were indigenous to the region. While as gardeners we tend to focus on pollinators, and perhaps to a lesser extent on the larvae of insects that eat our plants, the species that returned in Melbourne broadly represented the entire ecological gamut, including detritivores, herbivores, predators, parasitoids, as well as pollinators (published separately). In fact, the most common returning species was the charismatically named “minute brown scavenger beetle,” reinforcing the idea that a functioning restored ecosystem relies on a wide range of insects, most of which we (or I at least) are completely unaware of, and the complex relationships among them.

Adapted from Mata et al., 2023, Fig. 2. The top row shows the change in the number of insect species in different ecological niches over a four-year period, with the baseline (BL), unplanted, condition compared to the “greening action” (GA) treatment where locally native species were planted. The second row similarly shows the increase in the frequency of those insect groups.

And so this is why I do this: with the hope that our local Philadelphia area insects remember as well. And by planting largely or exclusively wild-growing local natives, I have a strong intuition that the insects that use those plants are already here, and therefore may not need as much help remembering, but all the help they can get in accessing the resources that may have been hard to locate or unpredictable in the past, but that we can provide in abundance, forming the base of a strong ecosystem once again. And perhaps someday widening our palette of locally native plants in the hope of restoring an ecology that hasn’t existed here for centuries.

The Mata et al. paper described in this post can be accessed for free at: https://doi.org/10.1002/2688-8319.12259