Wednesday, June 20, 2018

Colorado's Native Bees

Leaf Cutter bee with leaf, photo courtesy

Colorado has over 950 species of bees, and all but a handful of these are native. Most of the few introduced (non-native) species that now call Colorado home were brought in accidentally. The most well-known non-native bee is the honey bee, an important pollinator of many of our agricultural crops, especially those that are also non-native. But our native bees, who for millions of years have co-evolved with our native flowering plants, are much more important, efficient, and effective pollinators for native fruits and vegetables. Many of these, like squash, tomatoes, and eggplants, cannot be pollinated by honey bees at all!

Colorado has the 5th most bee diversity of any state in the US with approximately 950 bee species that range dramatically in color (black, brown, grey, blue, green, red, orange, and yellow), shape (round, oval, elongate, and even triangular), hairiness (almost bald to completely fuzzy), and size (smaller than a gnat to over an inch).  A comprehensive list of Colorado bee species is reported in The Bees of Colorado.

When you think about bees, you probably envision a swarm of black and yellow insects busily buzzing around a hive. Not only are most of Colorado’s bees not black and yellow, only about 12% of Colorado’s bee species are social. A social insect lives in a colony with a queen, worker and drone (male) “castes”.  The majority of bee species in Colorado, about 70%, are solitary with each female constructing and provisioning her own nest, much like a bird does. These include the plasterer bees, masked bees, mining bees, digger bees, mason bees, resin bees, leafcutting bees, and some sweat bees. The remaining 18% of Colorado’s bee species are parasitic on other bees. 

 The life span of an adult bee may vary from only several weeks to years in the case of a queen honey bee. Our solitary bee species survive the winter still in the nest they developed in, usually in the larval stage, with the previous year’s adults all dying with the arrival of freezing temperatures in the Fall.

Pre-drilled holes for solitary bee nesting, photo courtesy Donna Duffy
Most of our Colorado bee species nest in the ground, although these nests are easily overlooked. The other place that bees typically nest is in wood. While a few species including our small carpenter bees will excavate their own nesting tunnels, many species nest in pre-formed cavities. Small cavities including burrows made by beetle larvae in wood or the pithy center of small twigs like roses or brambles provide nesting sites for about one third of Colorado bee species (masked bees, mason bees, leafcutting bees).  The bees that nest in these small cavities add nesting materials to their tunnels, such as leaves, mud, plant fuzz, and resin. When their nest is completed, they plug the tunnel entrance. 

For more information about native bees, check out USDA's Bee Basics: An Introduction to Our Native Bees.