Nest building isn't just for the birds

Have you ever wondered what insect carves out the leaf edges on your garden plants? If the leaves look like this cut-leaf daisy, American beautyberry, or rock rose, you may have leafcutter bees in your garden.

Several native bees have made nests in my native pollinator garden this May; I spotted a sunflower bee entering her ground nest in the garden soil; and my bamboo-reed bee houses have mason bee nests plugged with mud plaster and leafcutter nests plugged with leaf plaster. These images show the laborious process that leafcutter bees go through to make nests and provide for their young.

To make her nest, a leafcutter bee performs a series of intricate steps. First, she uses her mandibles and front legs to scrape and smooth the inner surface at the back of a reed. Then, she visits many flowers to collect pollen and nectar that she brings back to her nest where she combs the pollen out of her tummy hair and mixes it with nectar. She packs the pollen and nectar into a loaf, filling an area about the length of her body, and then lays an egg on it. The pollen-nectar loaf will provide all the nutrients for one growing larva.

She then plasters over the pollen pack with a coat of leaf mastic and smooths it with saliva lacquer. About the length of her body from this wall, she carves a grooved ring around the inside of the reed where she tucks small pieces of leaves. Her large mandibles make clicking sounds as she chews the leaves into a ragged sticky fringe where she tucks large leaf pieces. She arranges overlapping leaf tips to look like a camera’s shutters and work like a ‘doggy door’. Then, she repeatedly climbs through the center of her trap door to fill the second chamber with pollen.

After she has stocked enough pollen for a larva, she lays a second egg on the pollen loaf. She then reinforces her leaf-door with a scaffold of plant fibers plastered with leaf mastic. After packing pollen, laying an egg, and walling off each chamber three or four times, she finally plugs the nest with a thick mosaic of plant fibers and leaves, thus culminating her engineering feat and architectural masterpiece.