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Biodiversity Blog

 

Nest building isn't just for the birds

by Laurel Treviño, Outreach Coordinator for the Jha lab

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.

 video1
 Click image above to watch a leafcutter bee using leaves to construct nest. (video: Laurel Treviño)

 

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.

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 Click on image above to see leafcutter bee continuing to labor over her nest. (Video: Laurel Treviño)

 

After hatching, the eggs will develop into larvae, metamorphose into pupae, and finally grow into adults. In about a month the adult bees will chew their way out of these incubator chambers. Males will emerge first and females last because the mother bee laid female eggs at the back of the reed and male eggs at the front.

Like this leafcutter bee, who built and provisioned her nest alone, most of the 4,000 bee species that are native to North America are solitary, while fewer species are semi-social and very few are colonial. More than 800 native bee species belonging to six families live in Texas. If you have a native plant garden in the Austin area, a few of the 200+ bee species that live in Central Texas might have made their home there this spring. Most of these native bees are ground-nesters, such as bumble bees, squash bees, and miner bees; but some are cavity-nesters, such as leafcutter bees, mason bees, and carpenter bees. Regardless of how or where they nest, most of them will pollinate your flowers, which will in turn produce more fruits.

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