Investigating Bumble Bee Nesting Habitat Preferences and Natural History Along the Lower St. Croix River

Abstract

The upper midwestern US is one of the most changed landscapes on the planet, where much of the native vegetation has now been converted to agriculture. This loss of habitat has negative impacts on a variety of species, including bumble bees (Bombus). Minnesota alone is home to 25 species of bumble bees, with numerous species at risk of extinction that can partially be attributed to habitat loss. In order to implement effective conservation action for these important insects, identifying their habitat requirements is key. Generally, bumble bees require three main habitat components to complete their life cycle: foraging habitat, overwintering habitat, and nesting habitat. The majority of bumble bee research has focused on foraging habitat and flower preferences of bumble bees, leaving a large knowledge gap regarding nesting and overwintering habitat. However, these aspects of the bumble bee life cycle are notoriously difficult to observe and the time required to locate such locations is often considered prohibitive, leaving them to be relatively understudied. This lack of information on the nesting habitat requirements of bumble bees has negative consequences regarding conservation action, as habitat needs cannot be adequately identified and therefore may be inadequately protected. In this thesis, I investigate the nesting habitat preferences of wild bumble bees in different habitat types along the Lower St. Croix River Valley in the US states of Minnesota and Wisconsin. I used a novel, systematic approach to locating bumble bee nests directly in their habitat, spending equal effort in each habitat to quantify bumble bee nesting habitat preference. I also document various aspects of bumble bee nest natural history including nest activity, survival, and interactions with other species, which is important for informing future research directions regarding nesting bumble bee biology and ecology. The findings from this study also inform the development of standardized nest searching protocol for finding bumble bee nests more efficiently.