Tuesday, July 25, 2006

Biting off more than you can chew

Just a quick post for today, to prove that I still exist (after a week-long field-trip followed by the whole beginning of a new semester thing).

Ever seen beautifully regular circles and ovals cut out of leaves in your garden? Maybe they looked like something had been eating very tidily, but those bits are not actually being eaten, but neatly snipped out and carried away by a type of bee called a Leafcutter (Megachile sp. such as the pictured M. serricauda). The females (ever the workers in the solitary bee world) snip two shapes (small circles and larger ovals) from leaves, carry them to a hole or crack (I've found nests in those little gaps you find between bricks in walls, bamboo canes are also apparently also used) and use them to construct the brood chambers. If you see those shapes in your garden you'd do well to watch them closely on a nice warm morning and hope a leafcutter comes around. They land in a few places and eventually select a good leaf (maybe by tenderness?), then astonishingly fast snip their way through the shape (as seen in the photo on the left). As the leaf cutout is removed it's curled between the bee's legs and as the last piece is severed the bee and leaf fall together into the air, whereupon the bee flies off too fast to follow in the direction of its nest.

As is generally the case with bees, the females collect pollen, moisten it with little nectar to form 'bee bread' upon which they lay an egg. For the leafcutter bees, this bee bread is made within a crack or hole that they've lined, with the oval leaf pieces, and is subsequently sealed, with the circular ones. Often a single hole has multiple cells constructed within it in a linear fashion (though I wonder if the first bee to emerge then chews through the rest of the cells to reach the entrance?).

Incidentally, the bee on the right is one that I encountered on a miserable and cold morning, and it appeared to have been caught out in the cold so to speak, and didn't make any effort to fly away.

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