By Deborah Lebow Aal
If you are reading this, you have some familiarity with, and/or, some interest in the interdependence of native plants and native insects. Some native plants provide the ecosystem with more benefits for insects than others. The measure I am using for ecosystem benefits is how many species of caterpillars a native plant hosts, because it is the best metric for ecosystem benefits that we have right now.* A review of why we are using this metric: Doug Tallamy, entomologist at University of Delaware, and native plant promoter extraordinaire, has researched and publicized this issue. The oversimplified explanation is that baby birds need an extraordinary number of caterpillars to fledge. Fewer caterpillars equals fewer birds. In general, native plants support caterpillars in much greater numbers than non-native species.
The best system we know of to find the number of caterpillar species hosted by each plant is the National Wildlife Federation’s (NWF) Native Plant Finder. This fantastic site lets you put in your zip code and find out which plants get you the biggest bang, or largest caterpillar species number, per plant. I will show you what came up for my zip code, in Denver, and I will contrast that with a Boulder zip, and a high altitude zip, in Silverthorne, CO (altitude 8,790). You will see that there is a difference between native plants in areas that are not too geographically distant, and certainly a difference when you are at altitude in Colorado.
Now this doesn’t mean you shouldn’t put in your favorite native plant, if it supports only three caterpillar species. Most likely it supports other native insects, and is quite beneficial to those
three caterpillar species. In fact, it might be the only host for that species. You might want to balance that Purple Prairie Clover (Dalea purpurea), e.g., hosting three caterpillar species, with a Chokecherry (Prunus virginiana), e.g., hosting many more. I am an advocate for having your favorite plant in your yard. With the amount of work we gardeners do, your yard should put a
smile on your face every time you walk out there. And, again, if it’s a native plant, it is benefitting the ecosystem. The more native plants, the better!
A word of caution. For my area in Denver, the best native plant I could plant for the highest
number of caterpillar species, according to the NWF database, is a willow (Salix). Willows
require a lot of water, so I will not be planting a willow in my water-thrifty yard, despite the fact that it can host an astounding 322 species of caterpillars. Willows typically belong in riparian areas near streams or wetlands. My point being, there are lots of things to take into account before planting any of these plants. It’s a good idea to do some research with the list you get for your zip code before going out and purchasing plants.
Here is the list of native plants hosting more than 50 species of caterpillar in my zip code in
Denver, 80209:
| Common Name | Latin Name | # of Caterpillar Species |
| Willow | Salix | 322 |
| Aspen, Cottonwood, Poplar | Populus | 262 |
| Beach Plum, Cherry, Chokecherry | Prunus | 261 |
| Maple, Boxelder | Acer | 140 |
| Rose, Sweetbriar | Rosa | 91 |
| Goldenrod | Solidago | 79 |
| Sunflower | Helianthus | 69 |
| Dogwood, Bunchberry | Cornus | 58 |
For Boulder, which you wouldn’t think would be that different, being 28 miles from the Denver zip code, I used zip code 80310:
| Common Name | Latin Name | # of Caterpillar Species |
| Oak | Quercus | 221 |
| Birch | Betula | 216 |
| Pine | Pinus | 202 |
| Alder | Alnus | 193 |
| Crabapple, Apple | Malus | 162 |
| Cranberry, Blueberry | Vaccinium | 142 |
| Blackberry, Dewberry | Rubus | 102 |
| Spruce | Picea | 95 |
| Elm ** | Ulmus | 89 |
| Fir | Abies | 86 |
| Douglas Fir | Pseudotsuga | 83 |
| Ash ** | Fraxinus | 81 |
| Serviceberry | Amelanchier | 81 |
| Hawthorne | Crataegus | 78 |
For Silverthorne, CO, I used zip code 80489:
| Common Name | Latin Name | # of Caterpillar Species |
| Blackberry, Dewberry, Raspberry | Rubus | 102 |
| Spruce | Picea | 95 |
| Rose | Rosa | 91 |
| Fir | Abies | 86 |
| Douglas Fir | Pseudotsuga | 83 |
| Serviceberry, Juneberry, Shadberry | Amelanchier | 81 |
| Hawthorne | Crataegus | 80 |
| New Jersey Tea | Ceanothus | 66 |
| Dogwood, Bunchberry | Cornus | 58 |
There are probably many reasons why the Boulder and Silverthorne lists are longer than the Denver list. I believe there is still ongoing research on plant/caterpillar associations, and the list may not be complete for Denver.
The biggest takeaway here is that trees deliver the biggest bang for the buck, for the
ecosystem. If you’re planting just a few plants to benefit the ecosystem, make sure one or more of them is a tree. I will now be planting a few more chokecherries and native rose bushes in my yard and a few fewer purple prairie clover (hosting only 3 caterpillar species), but I will still be planting those prairie clovers!
- We want to note that the research on caterpillars as a measure of ecosystem benefits has been focused on East coast ecosystems. In Colorado, there may be better metrics, but we have yet to find one. Caterpillars are important elements in the food web, so we will focus on them here. We do have different insects, different birds, and different ecosystems than those on the East coast. Should more regionally specific metrics be developed for Colorado, we will review and update this information.
- ** These are on the NWF list, but are not native to Colorado