Specialist Insect Relationships
Let’s get technical, technical! (A nod to Oliva Newton-John)
In our first post in our series to “Support the Pollinators” in honor of World Bee Day on May 20th, we showed you how by utilizing a broad range of flower shapes and bloom times, your project could support a wide array of native insects. Today, we want to highlight specific plants that support very specific insects - those that are now rare and federally endangered.
Generally speaking, there are two broad categories of pollinators: generalist or specialist pollinators. Most pollinators are generalists meaning they consume a wide range of pollen from different plant species. Specialist pollinators evolved a relationship with a few or even just one plant species. Specialist bees evolved to emerge from their nest at the same time as their host plant begins to flower ( UC Berkely Urban Bee Lab).
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It is estimated that “roughly 25% of the ~770 species of bees native to the Eastern United States are pollen specialists. Pollen specialist bees coevolved a continuum of generic and specific associations with flowering host plants or pollenizers” ( Jarrod Fowler).
According to Fowler, 23% of Delaware’s native bees are specialist pollinators with 51 species total, and 21% of species of Pennsylvania are specialists with 70 species. Knowing this makes it even more important to include plants in your project designs that can help support our local native pollinators. We’ve all seen the fashion tshirts that say “Save the Bees” with mostly non-native flowers on the front meant to attract the European honey bee. European honey bees aren’t the ones facing decline - our native pollinators are.
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What to Plant
We’re challenging each of us to think deeper about supporting our local native pollinators.
There are a few plant families that are known heavy-weights for supporting many species of pollinators, both generalist and specialist alike. Fowler writes “The most recurrent host plant family among pollen specialist bee species was Asteraceae (59 bee spp.). The most recurrent host plant genera (N = ~100) associated with pollen specialist bee species were Solidago L. (39 spp.), Helianthus L. (35 spp.), Symphyotrichum Nees (32 spp.), Rudbeckia L. (26 spp.), Chrysopsis (Nutt.) Elliott (19 spp.), Grindelia Willd. (18 spp.), Coreopsis L. (17 spp.), Heterotheca Cass. (16 spp.), Salix L. (14 spp.), Verbesina L. (14 spp.), Bidens L. (12 spp.), Pityopsis Nutt. (12 spp.), Cirsium Mill. (10 spp.), and Vaccinium L. (10 spp.).” (Jarrod Folwer)
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Did You Read That?
By including these beautiful perennial favorites, you’ll be supporting a few hundred different species of specialist bees:
But if you want to get—technical, technical—here are some specific plants we grow that support specialist pollinators.
Plant Hosts for Specialist Pollinators
(Specialist bees relationship information from Cornell University)
| Plant |
Insect |
| Asclepias spp. |
Monarch butterfly |
| Aster spp. |
Specialist bees: Andrena asteris, Andrena canadensis, Andrena chromotricha, Andrena nubecula, Andrena placata, Andrena simplex, Melissodes druriellus, Melissodes subillatus, Pseudopanurgus pauper |
| Aster divaricatus |
Specialist bees: Andrena canadensis, Andrena placata, Pseudopanurgus andrenoides |
| Geranium maculatum |
Specialist bees: Andrena distans |
| Heliopsis helianthoides |
Specialist bees: Melissodes agilis, Melissodes trinodis, Megachile pugnata, Andrena accepta, Andrena aliciae, Andrena helianthi, Perdita bequaerti, Paranthidium jugatorium |
| Heuchera americana |
Specialist bees: Colletes aestivalis |
| Lupinus perennis |
Kerner blue butterfly |
| Monarda sp. |
Specialist bees: Dufourea monardae |
| Rudbeckia lacinata |
Specialist bees: Andrena aliciae, Andrena rudbeckiae, Colletes compactus, Melissodes agilis, Melissodes boltoniae, Melissodes druriellus, Melissodes subillatus, Melissodes trinodis, Paranthidium jugatorium, Pseudopanurgus andrenoides, Psuedopanurgus compositarum |
| Solidago caesia |
Specialist bees: Andrena asteris, Andrena canadensis, Andrena chromotricha, Andrena nubecula, Andrena simplex, Colletes solidaginis, Melissodes druriellus, Perdita octomaculata, Andrena placata, Pseudopanurgus aestivalis |
| Solidago gramnifolia |
Specialist bees: Andrena hirticincta, Colletes simulans |
| Zizia aurea |
Swallowtail butterflies, Andrena ziziae bee |
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Let's Do More!
In addition to helping support our native pollinators by planting native plants, here are ways we can support them by building their habitat.
- Better Land Use Planning. No amount of planting small pocket gardens can offset increasing habitat destruction. In our local municipalities, we need to advocate for better land-use planning to maximize the use of areas already developed for human use and to minimize further undeveloped land encroachment.
- Provide a variety of nesting sites. A lot of specialist bees are solitary in nature and nest in cavities, make tunnels, or burrow into the soil. Some bees nest in sandy, loose soils while others nest in hollow stems of plant material. There are great books (listed below) that can help direct you to develop habitat for your local specialist pollinators.
- Turn off the lights. Lights on at night can interrupt diurnal/nocturnal cycles for wildlife. If possible, turn off or limit the amount of light being used at night.
- Provide a puddle. A small puddle or a birdbath with some rocks in it is great for thirsty pollinators in the heat of the summer. It doesn’t have to be very big or deep, just somewhere they can get a drink.
- Build gardens at the base of trees. A number of insect species spend some part of their lives in the tree canopy. When the leaves fall, the insects hibernate in the leaf litter. Building a garden at the base of trees gives the insects a better landing place than mowed grass that will be disturbed regularly and keeping the cover of the leaf litter will help hibernating insects.
By building a better habitat for specialist insects, we’ll also happen to build better habitat for generalists who can adapt to anything. It’s kind of like how we build ramps and elevators as ways for people to move around buildings. Some people may be fine with taking the stairs but a few may not have the mobility to use stairs. By including ramps and elevators in a building design, it increases accessibility for a greater number of people to use a space. By focusing energy on including those with particular needs, we’ll be building an environment where more are welcome. Build it and they will come!
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Further Reading
Jarrod Fowler Pollen Specialist Bees of the Eastern United States with an extremely useful chart listing rare/uncommon specialist bee genera and their preferred food source with bloom times to really help select plant palettes to support native specialist bees.
Heather Holms’ Why You Should Plant a Garden That’s Wasp Friendly in New York Times April 13, 2022.
Dyke, et al. Creating a Pollinator Garden for Specialist Bees Cornell University
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