Megachilidae – Leafcutter and Mason bees

This family of bees contains the mason bees and the leaf cutter bees. The females build nests to house the larvae and  use either mud (mason) or leaves (leaf cutter) to construct the nest.

Photo credit Flickr user: Bob Peterson

Photo credit Flickr user: Bob Peterson

They tend to create their nests in wood holes or twigs rather than nesting underground  and they do not carry pollen on their back legs but rather on the underside of their abdomens.  It is important to note that both of these types of bees do not usually bore into wood like carpenter bees, instead they nest in holes already drilled by woodpeckers or other insects.  They may also utilize rooted pithy stem structures that are partially hollow.

Population numbers are higher in the western states, especially the blue orchard bee. This bee is very important for the the pollination of fruit trees and in particular, sweet cherries and almonds.   In these western states, farmers are now providing drilled boards as nesting sites to promote bee recruitment.  However, both types of bees have ranges that extend into Georgia.

Megachilidae in your garden

You will most likely know if you have a leaf cutter bee in your pollinator garden when some

Photo credit to Flickr user: bramblejungle

Photo credit to Flickr user: bramblejungle

of the leaves on your plants begin to display characteristic patterns where circles have been punched out on the leaves. The bee will then use this leave material to build its nest, hence the origin of their name. They collect the leaves to create individual nest cells lined with the cut leaf and filled with nectar and pollen. The egg is laid and the cell is closed.  She then repeats  this process throughout the tunnel, producing a series of tightly packed cells.

A finished nesting tunnel may have a dozen or more cells inside a tube that is 4-8 inches long.

See the video below to witness a leafcutter bee creating a brood cell inside a wooden tunnel built with a plexiglass portion for viewing.

If you want to know if you have mason bees in your garden, again look for evidence of nesting sites. Just like leaf cutters they have an unusual brood cell method. Again, utilizing hollow pithy stems that have been bored out by other insects, mason bees pack their nests with mud,clay or chewed plant tissue.
The pollen and nectar plant mass is  gathered by the female by visiting many flowers and therefore becoming an important pollinator . The pollen and nectar is then deposited in the nest and the egg is laid on top. The bee then creates a partition of mud which doubles as the back of the new cell.

As described above, the blue orchard bee , Osmia lignaria is an important member of the Megachilidae family. It is a Mason bee that is very economically important for early spring fruit in Canada and the US.

Orchard mason bees, like all mason bees, are very shy and will only sting if they perceive serious danger.  The stinger is actually an egg guide. Because of their docile behavior, mason bees are preferred by people who desire pollination in urban settings.

Remember, if you would like to keep and cultivate blue orchard bees in your pollinator garden or growing area, its species is divided into two subspecies O. lignaria propinqua and O. lignaria lignaria. The division is set around the geography of the Rocky Mountains. USDA entomologists have strongly suggested that these species be kept to their native origins. 

  • Osmia lignaria propinqua (west of the Rockies)
  • Osmia lignaria lignaria (east of the Rockies)

So, only purchase Osmia lignaria lignaria species for your garden and help keep the Mason orchard bee where it should be!

See the blog page here for instructions on how to create your very own bee box for nesting of leaf cutter and mason bees.