These tubes can be used by a number of species including Mason Bees (Genus Osmia), Leafcutter Bees (Genus Megachile), and Grass-carrying Wasps (Genus Isodontia). The bees are what we want, but the wasps are okay too (they do some pollinating). These are all solitary species that do not nest in colonies. In the wild, these species typically nest in holes excavated by beetles or in plants that have hollow stems – the nesting tubes are a substitute for these natural cavities.
Each female Mason and Leafcutter bees gather pollen and place it in a ball at the back of a nesting tube before laying a single egg on the ball of pollen. She then caps off that section of the tube with a ball of mud (Mason Bees) or a circle cut from a leaf (Leafcutter Bees). She then repeats this process until the entire tube is full. The Leafcutter bee will also line the inside of the tube with sections of leaves before collecting pollen. The larvae will develop inside the tubes, eventually forming a pupae. They will typically not emerge as adults until next year.
The Grass-carrying Wasp does not gather pollen although she does eat some of it (along with nectar). Instead she stings crickets, katydids and other insects to paralyze them before stuffing them into the tube. She then lays a single egg – when the egg hatches, the larvae eat the paralyzed insects. After laying an egg she seals up the chamber with bits of grass and repeats this process until the entire tube is full.
One other insect that may be seen entering the tubes is a type of bee known as a Cuckoo Bee (multiple genera). These bees are nest parasites. They lay their eggs in the nests of other bees. Because they do not provide for their own young they lack the pollen carrying structures and hairs found on other bees. They look more like wasps than bees. I did see what I though was a Cuckoo Bee leave a nest tube at one point.
All of these species are very nonaggressive and will rarely sting unless grabbed or stepped on.
This first picture is labeled to show what I could see in each tube.
|A nesting bee pears out of a cardboard nesting tube at the Mt. Pleasant Discovery Museum|
|One done and a lot more to go - A Mason Bee lines a nesting tube with mud at the Saginaw Chippewa Academy|