During a training hike for volunteer nature guides last week, a fellow naturalist pointed out a series of pea-sized holes in the ground. I walk along this same trail regularly and had never noticed them. As our group stooped around these holes, shivering on this cold but sunny spring morning, a tiny head crept slowly out of the one of the holes. It was the head of a mining bee! Unlike honeybees, short-tongued mining bees are solitary creatures and do not form large socially organized nests. Instead, female mining bees dig a single vertical burrow in the soil, creating brood cells along the sides for eggs. The female prepares the burrow for her offspring by waterproofing the tunnel walls using a secretion from a gland in her abdomen. Like every good mother, she then stocks the pantry, filling each brood cell with a delicious buffet of pollen and nectar collected from spring wildflowers. Once the cells are well stocked, she lays an egg directly on top of each food mass. When the larvae hatch, dinner is ready! The babies will reach adulthood by autumn and overwinter below ground in their cozy cell. These adult offspring will finally emerge from Mom’s burrow the following spring in search of a mate. The females of the brood will then mine new burrows of their own.
Mining bees are also called Adrenid bees because they belong to the family Adrenidae. There are over 1,200 different species of Adrenids in North America. These mining bees are superior pollinators in cool weather and are a perfect match for spring wildflowers, such as spring beauty (Claytonia virginica) and swamp buttercup (Ranunculus septentrionalis). This family of bees is one of the few pollinators of large-flowered trillium (Trillium grandiflorum) that you can see blooming now in high-quality woodlands throughout Lake County. Want to learn more about who pollinates what? Visit this great website about flower-visiting insects in Illinois.
Given their solitary nature, mining bees often go unnoticed. It’s easy to walk by their small holes in the ground without ever noticing, as I had done many times along this trail. However, given the ideal soil conditions large numbers may mine nests near each other, which is exactly what I witnessed a few days later. My family laid a blanket in an ideal picnic spot on a warm, sunny spring afternoon. Apparently, some mining bees considered it a perfect spot as well. I kept reminding my family that although the females can sting, they are very mellow and rarely do. With the fear of a sting alleviated, we sat there silently and watched hundreds of male and female bees in a swirling display of courtship flight. You can watch these fascinating bees yourself. Visit a Lake County Forest Preserve close to home, and look for 1/4-inch holes in dry ground in a south-facing area near wildflowers.