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Bug of the Week is written by "The Bug Guy," Michael J. Raupp, Professor of Entomology at the University of Maryland.

Spring sunshine heralds the appearance of plasterer bees: Colletes


What is the guy with the camera looking at?


With Old Man Winter finally on the run, last week Bug of the Week  visited hard working honey bees as they revved up for a season of pollinating crops by enjoying spring wildflowers. This week on a freakish afternoon when temperatures soared to the 70’s, I visited a nearby golf course to visit one of our native pollinators, delightful plasterer bees.

Spring is the season that many of our native pollinators are busy at work. Why do so many insects gather pollen? A remarkable deal was struck between insects and flowering plants some 100 million years ago. Plants agreed to provide insects with food in the form of nectar and pollen, and insects agreed to reliably carry pollen from one plant to another to complete the task of sexual reproduction. Along with beetles, flies, and butterflies, bees are among the premier pollinators on the planet. Plasterer bees are some of the very first native pollinators to appear each spring. They have fascinating behaviors of building galleries in the ground and then lining the interior surface of their burrow with a thin, glossy, translucent material produced by a gland in their abdomen. Plasterer bees use their tiny mouthparts to remove the soil while constructing their galleries. The excavation is accompanied by a buzzing sound that may help loosen particles of soil and aid in the digging process. The bee’s mouthparts are also used like a mason’s trowel to spread the glandular secretion on the inside of the burrow before it dries into a cellophane-like coating. How clever! This habit of sealing their galleries gives this bee the common name “plasterer bee”.  

When soil conditions are just right, plasterer bee galleries can be very numerous.

Plasterer bees are relatives of honey bees and bumblebees but, unlike their cousins, these bees are solitary. Rather than living in a communal nest, each female plasterer bee constructs a subterranean gallery of her own to serve as a home for her brood. Burrows are provisioned with a semi-liquid concoction of nectar and pollen from flowering plants that bloom early in the spring. This yummy delight is food for bee larvae that develop during the summer and fall within the galleries. Plasterer bees emit a delightful citrus-like odor when handled. This odor is a pheromone produced by a gland in the head of the bee. The pheromone contains linalool and other aromatic compounds that may help plasterer bees find nesting sites, food sources, or potential mates. Although they are not considered social insects, large numbers of plasterer bee galleries are often abundant in close proximity in sandy soils with thin vegetation.

While exploring the nesting site at the golf course near a fairway, I was delighted to see dozens of small plasterer bees zooming inches above the ground. While swarming bees at the margin of play might dismay some golfers, no cause for worry or fear is warranted. Unlike yellow jackets, bald-faced hornets, and other stinging terrors, plasterer bees are docile and extremely reluctant to sting. Remember, each female bee is a mother, and to risk her life by stinging a human could mean instant curtailment of her reproductive potential should she die in the encounter. Over large areas of this balding zone in the rough, several burrows could be found in each square meter of ground. The plasterer bees were not responsible for the balding turf. They simply colonized areas where the turf was naturally thin. If you see swarms of small hairy or metallic bees constructing burrows or emerging from galleries in your garden or lawn, please resist the urge to treat them with insecticides. Several kinds of native pollinators including anthophorid bees, yellow faced bees, andrenid bees, halictid bees, and plasterer bees nest in the ground. Enjoy these beauties and give them a break. They pollinate plants and keep our planet humming.


A sunny afternoon in March is the perfect time for romance if you are a plasterer bee.



Bug of the Week thanks native bee guru Sam Droege for inspiration and identification of the bees in this episode. The wonderful article “Ecology, Behavior, Pheromones, Parasites and Management of the Sympatric Vernal Bees Colletes inaequalis, C. thoracicus and C. validus” by S. W. T. Batra was used as a reference.