Oh those leafcutter bees!

A Garden Mystery Solved

(previously published in the Green Valley News and Sahuarita Sun – reprinted with permission)

Every spring in the Sonoran Desert a new crop of gardeners ponders the mystery. Someone or something is leaving the foliage of flowering plants in a lacy tatter. Perfect semicircles are cut from the leaves of blue plumbago, yellow bells, bouganvillea and others. Some leaves have more than one missing piece.

According to Pima County Extension Master Gardener, Ted Cline, the culprit is the leafcutter bee. Unlike the honeybee that originally came from Europe and now often interbreeds with aggressive African bees, the leafcutter bee is a native species. This small bee doesn’t live in a hive like the honeybee.

The leafcutter bee lives a solitary life. The leafcutter female spends much of her time collecting pollen and nectar to feed the larvae that will become the next spring’s pollinators.

There are many species of leafcutter bees. Many are part of the genus Megachile, a Latin word meaning large or great lips, a reference to the strong jaws with which the bees precision-prune your plants. These bees and their relatives, the equally passive resin and mason bees, are important pollinators in the western United States.

Don’t bother trying to get rid of the leafcutters by spraying your plants. Because the bees don’t eat the leaves they cut, spraying with insecticide won’t get rid of them. More importantly, we need these pollinators to keep our flowering plants reproducing and our desert blooming.

Cline the master gardener says, “You have to share with Nature. They [the bees] take a little bit, we take a little bit.”

Stealth Pruners in Action

If you listen carefully on a spring morning, you might hear hundreds of leafcutter bees humming in the mesquite and the palo verde trees. These bees are most active from March through May, when temperatures reach at least 70 degrees.

If you watch closely, you might see leafcutter bees stealthily pruning your plants. Don’t blink, though, or you’ll miss the whole process.

If you’re lucky enough to see one of them in action, you’ll notice that the creature seems to be on a serious mission. Hovering close to your favorite plant, the tiny leafcutter bee (some species of which have flat, striped abdomens) will appraise first one leaf, then another until it finds one it likes. Then the bee will land and in a matter of seconds slice off a piece of leaf, roll it into a tube and carry it away.

The bee’s mission is a serious one. Each leafy cylinder is transported to a nesting site close by where it will be inserted into a soft plant stem or piece of rotting wood, creating a small cell to be filled with pollen and nectar. Once a cell is filled, the bee lays an egg that will produce a new bee by the following year. A tunneled-out stem or a dead piece of wood might contain a dozen or more of these cells—filled, sealed and placed end-to-end like boxcars.

Bee Habitat as an Art Form

Greg Corman, an artist, horticulturist and garden designer in Tucson, is a fan of our solitary bees. With BS and MS degrees in agriculture from the University of Arizona and the University of Maryland respectively, Corman understands the importance of pollinators. He also understands that, with our preference for tidy gardens, we often remove the dead stems and stumps that leafcutter bees and their relatives use as nesting sites.

To combat the loss of solitary bee habitat, Corman designs functional art that is pleasing to homeowners and attractive to solitary bees. Out of recycled wood and other materials, Corman crafts artistic bee habitats, boring tunnels of just the right length and circumference to attract leafcutter bees, resin bees and mason bees, all nonaggressive solitary bees that don’t sting or attack people.

Corman has been creating bee habitats for almost 5 years and loves to share information about solitary bees. He considers solitary bees “great gateway bugs.”

“They’re safe and easy to watch and can help people get over their phobias about insects. It’s important for parents to get children over the ‘ick’ factor about bugs,” says Corman.

Corman creates both small and large habitats. You can see large versions of his habitats in Tucson at the Arizona-Sonoran Desert Museum and Tohono Chul Park and at Miraval, an exclusive resort in Catalina, Arizona.

Examine one of Corman’s habitats, and you’ll see rows of holes leading to tunnels in the wood. Once a bee has filled a tunnel, it will seal the hole with a waxy substance, creating a little cork that’s visible to the naked eye.

According to Corman, the bee habitat at Arizona-Sonoran Desert Museum is a bench with bee tunnels drilled into it—a testament to how safe and non-threatening these solitary bees are. Corman’s habitats do not attract honeybees or aggressive Africanized bees.

 

 

Most bees are not aggressive

According to the Arizona-Sonoran Desert Museum, there are more than 1000 species of bees within the Sonoran Desert bioregion, and the area surrounding Tucson is home to more kinds of bees than any other place in the world, except possibly certain deserts in Israel.

Once you’re aware that we have so many types of bees in our desert region, you’ll see them everywhere.

Cassie Burruel, a senior staffer at the Pima County Extension office in Green Valley, Arizona says, “Most bees are pretty mild in nature. The Africanized bees are your problem bees.” Burruel has never heard of solitary bees stinging. “It’s rare,” she says.

“I’ve never been stung by one,” says Corman

Information on the Arizona-Sonoran Desert Museum website confirms that solitary bees are docile and rarely sting unless handled or swatted. Solitary bees do not travel in a swarm.

If you see a swarm of bees, experts advise you to stay away. It’s difficult to tell Africanized honeybees from other honeybees, so leave removal of a bee swarm to the professionals. For safety’s sake, assume that any swarm of bees is a swarm of Africanized bees and contact your local extension office for information on where to find bee removal experts.

If you’re interested in observing bees, go for the solitary bees—like those little guys so intent on pruning your plants. They’re harmless and great fun to watch.

Originally published in the Green Valley News and Sahuarita Sun (rights to reprint reverted to author two weeks after publication.)