Solitary Bees
Storing, Harvesting, and Incubating
Leafcutter Bee Cocoons
Leafcutter Bee Nesting Tube Anatomy
In the back of a nesting tube, a female leafcutter bee will start to build a little thimble-shaped leafy cocoon. She’ll add a little pollen and nectar loaf and lay one egg on top, then seal the cocoon with more snippets of leaves. She’ll repeat this process until she runs out of space, then add an extra thick layer of leaves to the open end to cap the tube shut.
Unlike mason bees, some leafcutters develop quickly and may hatch that same summer, giving you a second generation of leafcutter bees.
Intact Fall and Winter Storage
Leafcutter bees can’t fly when it gets to be below 60°F. Around late summer or early fall, you can remove nesting materials from your bee house. Store the nesting materials in a fine-mesh bag (to protect from tiny predators) and store the leaf-capped end facing up (so the larvae sit on their pollen loaves). Don’t open any nesting tubes or disassemble any wooden trays. To mimic natural temperatures, store the nesting materials within the fine mesh bag in an unheated and unconditioned shed or garage. DO NOT KEEP THEM IN THE REFRIGERATOR, or their little leafy cocoons will get moldy.
Harvesting Leafcutter Bee Cocoons
Harvesting cocoons helps keep your leafcutter bees healthy and also allows you to take inventory. This is best done in early spring, around the time you’re releasing your mason bees! The leafy cocoons within a tube will all be joined together like one long cigar, but they will naturally break into individual cocoons when you handle them.
Make a gauge stick to check for partially filled tubes. Take a bamboo skewer and mark it at the length of the nesting tube. Gently insert into your tubes that don’t have a leaf cap on the end. If the mark protrudes out of the tube, there is at least one nesting chamber inside. If it doesn’t protrude, the nesting hole is empty. Set it aside and use it next summer.
For cardboard tubes, just tear or snip and unravel.
For reeds, pinch the leaf-capped end between your fingers and the reed will start to split or carefully split the leaf-capped end with a blunt butter knife. Since there is an empty chamber at the open end of the reed, you don’t have to worry about accidentally harming a cocoon. Pry the reed apart and gently remove cocoons with a Phillips-head screwdriver or popsicle stick held at a 45° angle. Catch cocoons in an empty tub or on newspaper.
For wooden trays, remove the rubber bands and any cardboard backing. Lift the first tray and gently remove cocoons with a Phillips-head screwdriver or popsicle stick held at a 45° angle. Catch cocoons in an empty tub or on newspaper. Make sure to check both the top and bottom of each tray. Brush away debris with a stiff brush or toothbrush. If you see chalkbrood, you can dip an old toothbrush in a mixture of water and bleach and scrub. Allow to dry and then reassemble before storage.
Incubating Leafcutter Bee Cocoons
DO NOT WASH LEAFCUTTER COCOONS, they aren’t waterproof like mason bee cocoons! Once leafcutter cocoons are harvested, store them loosely in a fine-mesh bag. To incubate, keep the bagged cocoons in a warm, dark location, like your water heater room. Monitor for emerging parasitic wasps, which may have been laid alongside your leafcutter eggs. Pteromalus (parasitic wasps) will emerge in about 9-14 days. Squish them as you see them to prevent attacks on your leafcutter cocoons.
The incubation period is temperature-dependent. You can expect leafcutter bees to emerge in about 42 days at 70°F, or in about 20 days at 84°F. The 6mm nesting holes that leafcutters use are also appealing to other wild bees and beneficial wasps. If you notice these emerging, release them!
When you begin to incubate your leafcutter cocoons, consider planting strawberries, beans, or peas for your leafcutters.
(Circling Back to) Releasing Leafcutter Bees and Cocoons
Once leafcutter bees begin to emerge, you can release both the hatched adults and intact cocoons outside.
The only exception would be if temperatures are >90°F. Intact cocoons can’t regulate their temperatures above 90°F, so in this case, they need to be kept inside or brought back inside. Release adult leafcutter bees as they hatch. Once the weather cools, you can place the intact cocoons back outside again.