Where Do Bees Nest In The City?

Bees of both sexes can find a wide assortment of urban flowers to meet their nectar needs. Female bees require pollen for the purpose of provisioning nests for their brood or young. The list of urban plants that attract bees for nectar and/or pollen is extensive and still growing. But where do females make their nests in urban settings?

At this time we have limited knowledge about specific nesting sites of urban bees, especially solitary species. However, based on wildland bee studies, two general nesting habits can be expected. The first and most common is ground nesting, and probably 85% of the bee species use this substrate to build their nests (see photos CD6-019, CD7-018). Depending on species, females excavate tunnels into a specific type of soil. At the end of these tunnels they make a series of brood cells, usually 3-10, out of various materials such as mud, leaves, or wood shavings. Each cell is provisioned with pollen, nectar, and one egg and then sealed off. The female bee does not continue to feed her brood as it develops as does the social honey bee. In some bee species there may be more than one generation of bees per year. In most there is only a single generation. Spring bees, for example, make their nests in March or April, and their offspring will develop slowly over the next 12 months and emerge a year later in March or April.

The second nesting type is cavity-nesting. That is, some bee species search for suitable preexisting cavities in old trees or in human structures of wood or metal, or even mason blocks for making nest cells. Once located, the same process of nest cell construction and provisioning occurs as with the ground nesters. Using this knowledge it is possible to simulate natural cavities with tailor-made wooden cavities to encourage nesting in home gardens. This can be done with trap-nest blocks (see CD7-005) or bee boards, which can be easily constructed and placed in a yard for convenient viewing of nest provisioning (see CD8-009). Shaded sites are best. Wooden traps can be opened to more closely observe a nest and its contents (see Cd8-014, 013). We recommend this kind of intrusion only for teaching classes or workshops, as once a nest is opened the bees inside will usually die from exposure.

Another type of cavity-nesting can be observed with large carpenter bees that chew holes into wood in order to build their nests. Sometimes they use door and window frames for this substrate. Although humans regard this habit as undesirable in the home environment, it reflects a pattern in nature where these bees would normally be nesting in dead tree branches (see CD8-016).