Walrus Moustaches
The Andrena Bees (Family Andrenidae, genus Andrena) are important spring pollinators. Some species are polylectic, visiting many different flowers, while many species are oligolectic, gathering pollen from a single family of flowering plants. All species are solitary and nest in the ground. The numbers in The Bees of the World by Charles D. Michener give an idea of the vast diversity of this genus: 1,443 species worldwide and 476 species in the western hemisphere with many species still to be described. The entomologist O. A. Stevens, who studied the Andrena Bees in North Dakota, found 53 species but suspected that there were probably close a hundred species total. No doubt Minnesota has similar numbers.
Like this pair of Andrena carlini, the Andrena Bees exhibit a high degree of sexual dimorphism; the males and females look nothing alike. This leads to confusion and complications in the attempts to identify the bees. It's helpful when a mating pair can be captured. This particular pair of bees was captured while perched on the leaf of Large-flowered Bellwort.
Female Andrena Bees can be recognized by their facial fovea, a kind of vertical eyebrow, wide and velvety. They also have well-developed scopea on their rear tibias for collecting pollen. Male Andrena Bees are noticeably smaller than the females. They have longer mandibles, lack the pollen-gathering scopea, and have adorable, walrus mustaches, probably their most recognizable trait.
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