Alright, folks! Time to round up the last of these native plant terms so we can be informed and ready to make the best decisions for our gardens come Spring, whether the size of your habitat is a little deck or half an acre. In part one of this blog series, I wrote about how we can define native plants, non-native plants, near-native plants, invasive plants, aggressive plants, exotic plants, and plants that provide ecological value. In part two, I wrote about how we can define cultivars, nativars, straight species, ecoregions, and local ecotypes. Now we’ll tackle the rest: specialist vs. generalist insects, host plants, keystone species, and pollinator plants.
Before we dive into these terms, however, we need to talk about insects—or as Edward O. Wilson puts it, “the little things that run the world.” Why are insects SO important? Here are just 4 reasons:
Reason #1: They perform pollination services
Pollinators are the poster children for invertebrate conservation. They are bees, moths, butterflies, wasps, beetles, flies, bats, and birds (to name a few). According to the U.S. Department of Agriculture, “Three-fourths of the world’s flowering plants and about 35 percent of the world’s food crops depend on animal pollinators to reproduce. That’s one out of every three bites of food you eat.” So, you know, every time you eat, thank a pollinator and remember why we want them around! Also, I’m sorry but some of them are really cute!
Reason #2: They provide pest control services
Insects like beetles, assassin bugs, flower flies, parasitoid wasps, and tachinid flies eat other insects such as aphids, leafhoppers, grasshoppers, wasps, sawflies, mites, and more. They keep them in check so their numbers don’t get too out of control. Some of these pest control volunteers are predators and some are parasitoids. Predators are very straightforward; they just hunt, kill, and eat pests. Parasitoids take a sneakier route: they use the pests (and sometimes the pests’ nests) as hosts to lay their eggs. When their babies (larvae) hatch, those babies feed on these pest hosts and eventually kill them. Hey, everybody’s gotta eat right? The big thing about these insects is that they help us by “minimizing reliance on pesticides that have harmful effects on pollinators and soil health.” – Xerces Society for Invertebrate Conservation
Reason #3: They provide decomposition and nutrient cycling services
According to the University of Maryland Extension, the process goes like this: “Nutrient cycling is when soil nutrients are taken up by plants, insects eat plants, and then those nutrients are reintroduced into the soil when dead insects and droppings are broken back down into nutrients via decomposition. Decomposer insects help clear dead animals and plants off the ground which would otherwise accumulate everywhere.” Who are these everyday superheroes? The insects you may call creepy crawlies, like termites, wood cockroaches, fly larvae (maggots), earthworms, pill bugs, and millipedes. So, okay, they’re not as cute as the fuzzy bumblebees and the pretty butterflies, but they are performing a job that I certainly would NOT want to do, and I bet you wouldn’t either.
Reason #4: They support the food web
If you stand outside on a sunny day, you might get a nice dose of vitamin D, but you know what what you’re not going to do? Photosynthesize. Only plants can do that. For us to get that sweet, sweet energy from the sun, we have to eat plants – or animals who eat plants. Like us, other animals cannot photosynthesize by standing in the sun and rely on eating plants – or animals who eat plants to survive. A lot of them specifically rely on caterpillars and other insects to get this energy. Here are a few examples from the University of Maryland Extension: “Terrestrial bird species, in particular, feed their babies almost exclusively with insects;” “Popular fish like salmon, bass, and trout eat insects, especially when they’re young;” “Grizzly bears will eat tens of thousands of moths a day to prepare for hibernation.” The takeaway here is this: fewer insects = fewer birds, fish, and bears—plus other insect-eating animals like frogs, spiders, bats, foxes, and opossums, who perform their own pest-control services, etc.
With this newfound appreciation for insects, let’s talk about the two camps they fall into.
Generalists vs. Specialists
Let’s say that you have a peanut allergy (I am sorry if that is actually the case, I know it can be a pain in the butt), and you go out to eat with friends who do not have one. In this scenario, you are a Specialist because there is a specific food you must seek out (peanut-free food), and your friends are Generalists because they can eat anything they want. Well, look, insects are just like us! Except it’s more than just about food. Generalists can visit most plants for nectar, pollen, and other resources they need for nesting. Specialists can only visit certain plants, usually in a specific plant genus or family, to get those same resources. For example: Bombus impatiens, the Common Eastern Bumblebee (a generalist), will visit many different flowers for their needs. In contrast, we have three bees in the Macropis family (specialists) documented in Massachusetts that do not collect pollen; instead, they collect oils specifically from native plants in the genus Lysimachia, commonly called Loosestrifes. According to UMASS Amherst Extension, we have about 81 specialist bees in Massachusetts, and there are hundreds of other insects that are specialists too, so when making plant choices is good to keep them in mind.
Host Plants
Host plants are native plants that insects rely on to reproduce. In one of the examples above, the oil-collecting bees bring those oils to their nest and lay their eggs on them so their offspring have a food source when they hatch. Another famous example is the Monarch Butterfly. This insect can only lay its eggs on a native plant in the genus Asclepias, commonly known as Milkweed. When the eggs hatch, the caterpillars can only eat Milkweed. It’s that simple. Just like you, in the analogy above (with your imaginary or real peanut allergy), can only eat peanut-free foods, Monarch caterpillars can only eat Milkweed, and the larvae of the oil-collecting bees can only eat oils from Loosestrifes.
Keystone Native Plants
To recap, native plants provide insects with the resources they need to complete their life cycle. Some native plants provide these resources for one or a few insect species, while others provide them for hundreds. These are what we call Keystone Native Plants. For example, in our region, according to the National Wildlife Federation’s Native Plant Finder, plants in the genus Asclepias (Milkweeds) support 12 species of moths and butterflies. Plants in the genus Solidago (Goldenrods) support 125 species. Plants in the genus Quercus (Oaks) support 473! All hail the mighty Oak!. Entomologist Doug Tallamy calls these “keystone” plants because, like the stones that support ancient Roman arches, the ecosystem would collapse without them.
Pollinator Plants
These plants support pollinators specifically, not necessarily insects that perform other ecosystem services. Many people assume a pollinator plant is anything that provides nectar or pollen, but it takes a little more than that. While some non-native plants provide some resources – think English Lavender or Salvia, which provide nectar – the best plants to support our native pollinators* are native plants that produce nectar, pollen, AND the specific resources they need to reproduce.
Always come back to Ecological Value
Please do not be overwhelmed by all this information. It is meant to empower you to make the right choices for your yard. It is your yard. You get to decide which plants live there and, therefore, who they support. My philosophy – after reading and listening to the thoughts of experts in the field – is that ecological value is the ultimate goal. Whether it is a native, a near-native, a cultivar, or a keystone species, ask yourself: Does it provide ecological value? Does it make your yard a better habitat for the wildlife that calls it home?
If the answer is yes, then you are in a great place. You do not need to rip apart your yard and get rid of all your non-native plants (except invasives—those definitely have to go!), but when the time comes to add more plants, think about choosing a plant that provides ecological value.
In case you’re curious, this is what I’m doing:
- I am working toward converting my small yard (a little over 1/8 of an acre) into 70% wildlife habitat.
- I use mostly native plants, but I also include some near-natives, a few cultivars (mostly shrubs), and a few native-to-the-U.S. plants.
- I strive to use a mixture of keystone native plants and native plants that support specialist insects, too.
- I am (slowly) getting rid of invasive plants (English Ivy!!!!!!), while other non-native plants that don’t spread aggressively are allowed to remain, like my Little Lime Hydrangea.
This work can sometimes be hard, but it is important and incredibly rewarding. I hope this information helps you on your own journey!
Cheers!
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