Please go to our Glossary link at the bottom of the page for explanations of scientific terms
Adults are fuzzy gray to brown bees about 1/2 to 3/4 inch in length. They cut neatly rounded pieces from edges of leaves from many different plants, particularly roses. The adult female stuffs the pieces of leaf into a tunnel or burrow to create a safe chamber for her larvae. She then gathers pollen to serve as food for her offspring.
In the greenhouse, the bees will think that a cactus pot on a shelf is an ideal place to store the larvae. They will enter, often through the drainage holes at the base of the pot and start to excavate a chamber, expelling the soil in the pot, usually onto the plants beneath the shelf! If left undisturbed, most of the soil in a pot can be removed and your cactus will start to show signs of drought and will shrink.
It is fascinating to watch the bees flying into the greenhouse with rose leaves and if it is only one or two, does little harm. In some years, however, it can involve very large bee populations and a lot of plants can be adversely affected.
"The optimal hole diameter is 7 - 8 mm. Space the holes in a regular grid on 1/2 inch or 1 inch centres. Make sure the holes are blind-ended tunnels that don't come out at the back of the canes.
The nests will routinely attract females of Megachile. These are large slender black and white-striped handsome bees with massive jaws. You will typically get 4 or 5 similar looking species. The end plug capping gives them away. Some species use masticated leaves, others use resin and sand and some form very messy looking debris end plugs with odd bits of bark, leaves etc. Enjoy!
These pollinator pets make great watchable wildlife. Hang the wood block nests up high. At least shoulder height to about 8 feet up under an overhang so they don't get direct sun or rain. Face them south or SE. The nests will overwinter just fine. After a few years, you may want to put up freshly drilled nests near the old ones.