Are native plants important to the plant-pollinator communities? Sometimes I hear somebody say: “When it comes to pollinators, all flowers are the same; after all, nectars are all alike” or “my English ivy must be good for pollinators because it is teeming with insect visitors”. Such comments show a lack of information and understanding, as I mentioned in “Wildlife Food and Non-native Plants”.
I have been photographing and studying pollinators for years, and I learned long ago not to waste time looking for them in the typical suburban gardens that are the pride of many of my neighbors. Nature centers and wildflower preserves are the source of most of my photos. Flying insects rarely visit a daffodil, forsythia or a tulip. Those that do so look rather puzzled, and leave promptly without visiting similar blossoms. Roses, the fancier ones, get no visitors either. The same applies to many of the “naturalized” plants, such as lesser celandine and garlic mustard. Recently, I spent time looking for pollinators on a few non-native flowers (lesser celandines, daffodils and forsythia), knowing what the results would be. I reported some of my observations in “Of Spring Beauties and Lesser Celandines”.
It is true that some non-native flowers get their fair share of pollinators. Dandelions, Queen Anne’s lace and English ivy come to mind. This is not surprising in places in which the habitat has been so profoundly altered that there are no native flowers in sight. What would pollinators choose if they had options? Also, which pollinators fare better when faced only with non-native flowers? Is it only the versatile ones, the Jacks-of-all-trades? What happens to all the others? And what happens to the wildflowers that rely on native pollinators? For instance, the non-native and invasive leafy spurge (Euphorbia esula) attracts many pollinators in North Dakota. This seems to have detrimental effects on nearby native flowers.
Doug Tallamy and his team have done extensive research on host plants for caterpillars. Over and over, native plants feed more caterpillars than non natives. There are hardly any similar systematic studies for pollinators. But we have good reasons to think that pollinators are best adapted to the flowers they co-evolved with. The North American Pollinator Protection Campaign lists some of these reasons on a factsheet.
Nectars are not all the same (“Nectar, Breakfast of Champions”). They are a lot more than sugary water; some contain amino acids and vitamins. This cocktail makes some nectars more suitable than others for different clients. There are even those that contain a little alcohol (“Nectar. A Drink with a Zing”). Has anybody heard of tipsy bumble bees?
Nectar isn’t the only food that flowers provide. Pollen is just as necessary, particularly for the most important pollinators, bees, also for some flower flies and a few butterflies. Adult bees may be relatively indiscriminate when it comes to nectar, but pollen for their babies is an entirely different matter. Bees tend to be more selective when it comes to pollen ranging from moderately- to highly-specialized. Some can only use pollen from one or from a handful of related species; that is why many bees are named after the flowers that are their main food source: spring beauty Andrena, azalea Andrena, squash bee, blueberry bee, rose-mallow bee, etc.
Pollinators vary in shape and size and in the length of their tongue. They are well-matched to the native plants with which they have co-evolved. They may not be able to manipulate introduced plants.
Flat, open flowers may be accessible to just about any kind of visitor, but those with more complex shapes have co-evolved with their pollinators, and don’t welcome others. This is the case of kudzu, that formidable Asiatic invader. In North America, it propagates mostly through runners and rhizomes because native pollinators can’t handle its flowers, so seeds are seldom produced. In recent years, a large black bee from Asia, the giant resin bee (Megachile sculpturalis), arrived in North America by accident and started spreading across the landscape. Guess what: This bee is a very efficient pollinator of kudzu’s flowers. So, now this invasive can also propagate by seed. Oh, joy!
Flowers that have been highly modified by horticultural manipulation, whether they are introduced or native, have lost most or all the cues that guide a pollinator to its food or they have lost their nectar and pollen entirely.
My answer to the question at the head of this post is: Yes, native plants are better than non-natives when it comes to pollinators. They are part of a community that has taken eons to reach a high level of integration. This cannot be compared to the occasional use of non-native flowers by pollinators. In cases in which a non-native invasive attracts many pollinators, it may be taking pollinators away from native flowers and disrupting the normal function of the ecosystem.
You may want to consult the Pollinator Partnership planting guides for pollinator gardens with lists of native plants by ecoregions. Also, Urban Bee Gardens has good guides for California, although they include some non-natives.
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