Whole leaf-petal pieces & the Leaf-cutting bees, Megachile

Amelanchier leave with Megachile leaf cuts.  Oblong cuts are used to line cells, Round cuts cap cells or plug nests.

Amelanchier leaf with Megachile cuts. Oblong cuts are used to line cells, Round cuts cap cells or plug nests.

Did you ever see perfect circles cut for your rose leaves or even flowers?  Did you wonder who was responsible?  Did you ever imagine it might just be a bee?  All Whole Leaf Piece plugs are made by Megachile, though not all Megachile make whole leaf piece plugs (some use resin or chewed vegetation).  You could say that Megachile are the ultimate leaf-cutting bee.

 

Whole leaf piece plugs are made from circles of leaf, often several overlapping, but sometimes just one solid piece is visible.  They can be loosely packed or “glued” into place.  The veins and often hairs are visible on the pieces of leaf.  Although they usually start out green, they will fade with time.  A variation of this are the bees that cut, not from leaves, but from petals.  Instant potpourri.

Whole leaf peice plug made from multiple leaf pieces, slightly curled on their edges.

Whole leaf piece plug made from multiple leaf pieces, slightly curled on their edges.

Loosely packed pieces of leaf that are not glued in place.

Loosely packed pieces of leaf that are not glued in place.

 

 

 

 

 

 

 

 

Slightly recessed whole leaf piece plug with veins and hairs clearly visible.

Slightly recessed whole leaf piece plug with veins clearly visible.

As whole leaf piece plugs age, they loose their green color, fading to yellow, brown and even sun-bleaching to light grey.

As whole leaf piece plugs age, they loose their green color, fading to yellow, brown and even sun-bleaching to light grey.

 

 

 

 

 

 

 

 

141013_B2_2014-06-18 cropped

 

We have a number of Megachile that plug with whole leaf or petal pieces around Colorado.  These vary in size from small to large.  You can find them in all hole sizes except the smallest ones. They’re starting to nest now and you’ll get to see them throughout the rest of the summer: some species have more than one generation, so watch your whole leaf piece plugs for holes. When you see holes, please submit those data, because that tells us your bees have successfully reproduced. Then you can watch for the daughters to reuse the nests.  We have had as many as 3 consecutive Megachile nests in a single tunnel:  Moms, daughters, and granddaughters!

 

Megachile rotundata, the alfalfa leaf-cutting bee, is a European species that was accidentally introduced to the United States, but is now managed for pollination in alfalfa seed production fields. They’ve done well enough for themselves that they’re incredibly widespread.  This is a common species in our bee blocks.

Megachile inermis elf0010 small

Megachile inermis, the gentle giant of Colorado’s higher elevations.

We also have many NATIVE species that nest in our bee blocks.  Megachile inermis, one of Colorado’s largest Megachile species, is found at higher elevations.  When not provided with a bee block to nest in, this species will nest in aspen logs and often use decaying wood in their plugs along with whole leaf pieces.

 

 

Megachile entering nest with leaf piece.  Note orange scopa.

Megachile with orange scopal hairs on underside of abdomen entering nest with a leaf piece.  Also, note whole leaf piece plug in the neighboring tunnel.

Another smaller native species is Megachile relativa.  These bees have a beautiful orange scopa, the pollen carrying hairs on the underside of their abdomen.

 

 

Our Megachile that plug with whole leaf pieces also line their cells with leaf pieces, like wallpaper for the nursery.

Cross-section of a Megachile inermis nest with 5 cells and whole leaf piece nest plug.

Cross-section of a Megachile inermis nest containing five leaf-lined cells and whole leaf piece nest plug made from many layers of cut leaves.

AND – if you participated in the project last year (thank you!) you may remember reading about Coelioxys, the leaf-cutting cuckoo bees. These bees sneak into a Megachile nest and use their pointy abdomens to slit the cell’s leaf lining and deposit an egg of their own.  Coelioxys eggs aim to hatch before the rightful nest occupants, so that they can mature faster and eat all the food stores right out from underneath the original occupants.

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