Ground bees, also known as solitary mining bees, are a common sight in lawns and gardens, often sparking curiosity about their behaviors. These bees are beneficial pollinators, playing an important role in local ecosystems without being aggressive. Their presence frequently leads to questions, especially about their fate once colder weather arrives.
How Ground Bees Survive Winter
Adult ground bees, observed foraging and nesting during warmer months, do not survive the winter. With the first hard frost or sustained cold temperatures in fall, these adults complete their life cycle and die. While the adult generation perishes, the ground bee species persists through winter. The species’ survival relies entirely on the next generation, safely hidden and developing deep beneath the soil surface.
This ensures that despite the death of all adult bees each year, new bees will emerge when conditions become favorable again. This cycle is a natural adaptation that allows these important pollinators to endure harsh environmental conditions. The offspring are insulated by the soil, protected from freezing temperatures and other winter hazards.
The Ground Bee Life Cycle
The survival strategy of ground bees through winter is intricately tied to their life cycle, which largely unfolds underground. Female ground bees construct individual burrows in the soil, often consisting of a main tunnel with several side tunnels. Within these side tunnels, each female creates a brood cell, provisions it with a ball of pollen and nectar, and then lays a single egg on top. The female then seals off the cell, and after provisioning several such cells, she dies.
Upon hatching, the larva consumes the stored pollen and nectar for its development. These pre-adult stages (larvae or pupae) spend winter within their underground chambers. They enter diapause, a natural insect hibernation allowing them to withstand cold temperatures and lack of food. Chemical changes within their bodies help prevent freezing, ensuring survival until spring. This developmental arrest can last for many months, with some species spending up to 11 months underground before emerging as adults.
What Happens to Nests in Spring
As temperatures rise in the spring, the new generation of adult ground bees, which overwintered as larvae or pupae, begins to emerge from the soil. They often create new burrows as they exit the ground, though they may also slightly expand existing ones. While the physical nest holes from the previous year may still be visible, these specific burrows are generally not reused by the newly emerged bees for nesting.
Ground bees frequently return to the same general areas year after year, forming aggregations of individual nests. This means that while a specific tunnel might not be reused, a favored nesting site may host new bees each season. The small mounds of excavated soil that marked the nest entrances during the previous active season typically wash away with spring rains, leaving little trace. The presence of ground bees indicates healthy soil and a thriving ecosystem, as these solitary pollinators pose no threat and contribute significantly to plant pollination.