Do the leaves on your plants have small, perfect circles cut out of them? They’re the amazing work of leafcutter bees, which are native, non-aggressive, and important pollinators. What, if anything, should you do if this happens in your garden?
If you see cutouts on your plants that look like this, you may understandably be concerned. Let’s take a look at the insects that are carving perfect circles in your leaves, the amazing reason they do it, and what to do if this happens to your plants.
Leafcutter Bees: Essential Native Pollinators
Leafcutter bees (Megachile spp.) are non-aggressive, solitary bees that are native to the desert southwest. These important pollinators are common in urban areas of Tucson and Phoenix, where they can be found gathering leaves from certain garden plants, especially roses and bougainvillea.
Leafcutter bees eat pollen and nectar from flowers, and pollinate flowers in the process. They don’t eat the leaves that they cut — the females use the circles to line their nests.
They are opportunistic nesters and lay their eggs in previously made holes in wood or stems made by beetles or other insects. They’ll also nest in holes found in man-made materials including decks, concrete, and stucco.
They wrap each egg in the leaf cutting along with pollen and nectar. I heard someone adorably describe these as “baby bee burritos.” 😉
It can take a female bee several hours to wrap one egg. The following spring her offspring will emerge.
What To Do if Leafcutters Are Using Your Plants
If leafcutters are having a go at your plants, your first thought will probably be how to prevent further damage, but the big picture is that it’s best to do nothing.
Here are some of the reasons this is one garden “pest” you should just “let be.” 🐝
Leafcutters Won’t Harm Your Plants
Leafcutters rarely harm a plant. They are a very small bee and can cause some cosmetic damage, but certainly won’t cause major harm to your plants. The plant will still be able to photosynthesize and grow.
Last summer 100% of the leaves on my small Mexican redbud tree showed leafcutter damage, and I was concerned. Like most gardeners, I wanted to do something. So I consulted the nursery where I bought it.
A wise staff member explained:
Redbuds and leafcutters are both southwest natives that evolved to co-exist. Change your mindset to accept leafcutters as an important part of the desert ecosystem rather than as a garden pest.
And so now I do. I hope you will, too.
Leafcutters Pose Low Risk to Humans
Solitary bees are not aggressive and their stings are considered mild. Only female bees can sting, and they rarely do so.
They Won’t Be Around for Long
Leafcutter bees spend most of their life cycle dormant. In the spring, the male dies soon after mating, while the female harvests leaves to wrap up her forty or so eggs.
Most of the leaf damage to your plants will occur in late spring and early summer over a period of about 2 months. By the time you notice the damage, they are probably near the end of their gathering cycle.
What You Can Do for Leafcutters
There are no successful ways to spray away leafcutters — either natural or synthetic. I’ve heard of people spraying plants with all kinds of things — essential oils, neem oil, dish soap, or even harsh chemicals like ammonia. But since the bees don’t eat the leaves, these measures aren’t successful.
If you’re still concerned about cosmetic damage, you can temporarily cover your plant with fine netting, frost cloth, burlap, or some other fabric barrier.
Or you can take the opposite approach and try to help and encourage the bees.
Leafcutters are often found in urban areas, but there are limited nesting places for them since dead and diseased branches and trees are usually removed. You can help them out by putting up a bee house.
You can buy one or build one — they are a pretty simple DIY project.
I don’t know if it’s a coincidence but as soon as I put up my bee house, the bees quit harvesting my redbud leaves.
Here’s a close-up picture of mine.
If you look closely, you can see that about a dozen tunnels are filled. I had so much fun watching the bees fill the holes, I can’t wait to watch the bees emerge in the spring!
Fascinating Leafcutter Facts
Let’s end with a few facts about these amazing insects.
There are approximately 5,000 species of bees in the US. Around 1,300 species live in Arizona and 600 – 700 species live in the Sonoran Desert, making it one of the most bee-diverse spots on the planet. Leafcutters and related species make up about 10% of Arizona’s native bee species.
One species of leafcutter (Megachile rotundatais) is important for Arizona agriculture. It is the key pollinator for alfalfa, a nearly $500 million industry.
It’s been observed that leafcutters sometimes favor one plant over another, even plants of the same species, but no one knows why. Researchers at the University of Arizona now have a clue.
They found leafcutters to be particularly attracted to leaves that are covered with Aspergillus, a very common fungus. There’s evidence that Aspergillus inhibits the growth of Ascosphaera, another fungus that causes chalkbrood, a disease that kills bee larvae. Pretty amazing!
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Author Bio
Deane Alban is the creator of Southwest Gardener. She is a science writer with a bachelor’s degree in botany from the University of South Florida. Gardening is her lifelong passion. She’s been gardening in Tucson for 15 years.
Photo Credits
University of Maryland Extension by Christa Carignan
“Megachile Centuncularis” by JRxpo is licensed under CC BY 2.0