The naturalist suffers a pleasant nuisance – not being able to walk 100 yards without being tied to the spot by some new and wondrous creature.
I’m afraid this applies to me and is often why it takes so long to hike (saunter is probably a better term for what I usually do) along a trail or get some task done here in the yard. And so it was last week when I was out doing some weeding and mowing. As I walked by a mulberry tree near the shed, I caught a glimpse of a green object hovering near the tree trunk. I tried to prop up this particular tree years ago using a stake and attached rope that ran through some plastic tubing. The tree had leaned over in a storm and I was hoping to help straighten it, while still protecting the bark. The rope rotted away, but the tube remained, captured by the tree bark. The green object hovered for an instant near one end of that tubing, and then disappeared inside.
I caught just enough of a glimpse to have an idea of what was happening, and I was thrilled. It looked like the work of a leafcutter bee, a native bee whose handiwork (or should I say, jawiwork) I see every spring.
You may have seen this where you live, small round holes in the edges of leaves. In my yard, the leafcutter bees are particularly fond of redbud leaves. It appears they favor thin leaves that lack a lot of thick venation. The result of the all this activity looks like an overly-ambitious person with a hole-punch has a grudge against your redbud trees. These bees cut circles of leaf material to use in making a nest chamber in some sort of hollow tube or in the ground (more on that in a minute).
I ran in and got my camera and was disappointed to see the bee leaving just as I got back. I had no idea how long it might be before she returned, so I squatted next to the tree and waited. Turns out, the entry into the nest chamber is quick, so I missed my photo opportunity on her next visit as I just could not focus fast enough. Her exit was equally quick, so I knew I had to come up with a plan B (or is it Plan Bee?). I set the camera up on a tripod and grabbed a twig and laid it gently into the tube entrance. I then pre-focused the lens on the twig just outside the tube, removed the twig, and waited again.
It worked. I heard her buzzing toward me, and pressed the shutter just as she approached the entrance. The camera caught her carrying a folded piece of redbud leaf as she approached the entrance to the tubing. She quickly went inside (I could see her movement inside the translucent tube) and took the leaf fragment to a mass of other greenery that was visible a couple of inches inside the tube entrance. She stayed a little over a minute and quickly departed. Within two minutes, she was back with another, smaller piece of leaf and repeated the sequence. But on her next visit, she was not carrying anything green.
This time, it was a load of pollen. This group of bees has an unusual feature compared to most bees – they carry their pollen on specialized hairs on their abdomen.
Bumblebees and honeybees have special structures on their legs, called pollen baskets, where they carry the pollen they gather.
Some speculate that by carrying pollen on the hairs of their abdomen, leafcutter bees may be more effective pollinators than many other types of bees. As they crawl around on flowers, it may be easier to transfer pollen to receptive flower parts if it is carried underneath their body instead of being packed into specialized structures on their legs.
I started timing the comings and goings of this industrious female and it turns out she was very efficient at gathering and depositing pollen into the nest. It generally took about 1 to 2 minutes to gather the pollen, and then another 1 to 3 minutes to deposit it inside the tube. I could see the green nest chamber through the walls of the tubing. When I worked at the museum, I photographed a nest chamber that had been exposed in a block of wood so you could see the details of their handiwork.
They construct cigar-like nests made of wrapped together leaf fragments. Each nest contains several cells. The female stocks each cell with a ball or loaf of stored pollen and then lays a single egg in each (each cell will produce a single bee). Nests are constructed in soil, in holes (usually made by other insects) in wood, and in hollow plant stems. They will also use a variety of human-made structures and readily take to artificial bee homes containing hollow tubes.
The museum’s collection also had one cell that was cut open to show the pupa and the “loaf” of bee bread (a mixture of pollen and nectar) that the female stocks as provisions for the developing young. Most leafcutter bees overwinter in the nest chamber as newly formed adults and then chew their way out next spring. One source stated that the last egg laid (that one closest to the entrance of the entrance hole) is the first to hatch, and so on, down the line.
The activity at the nest was complete by the next day. I will now keep an eye on this tubing to see if produces some new leafcutter adults next spring. The genus name, Megachile, literally means big lip, or big jaws, in Greek. Here’s wishing these big jaws a successful birth and hatching. Now that I know more about the cause, I’m starting to like those hole-punched redbud leaves.