Wild Bee Cocoon Guide

Wild Bee Cocoon Guide

Chances are, your bee hotel or bee house will attract a hole-nesting wild bee.

You might be surprised to find strange cocoons during your mason bee harvest in the fall or leafcutter bee harvest in the spring. We want to help your local bee population thrive - here are our expert tips that can help you understand your bee house guests.

The world is home to a huge diversity of wild bees. Worldwide, there are at least 21,000 bee species and North America is home to 4,000 native bee species. We estimate that there are about 1,000+ bee species that nest in holes. The world is also home to a huge number of wasps species, many of which are solitary wasps that nest in holes. Solitary hole-nesting wasps are beneficial insects that hunt garden pests and each wasp species have their favorite prey.

Bees and wasps can overwinter as:

A cocoon spun by the larva; like those made by our spring mason bee

A protective cocoon built by the mother bee; like the leafy cocoons made by our summer leafcutter bees

• Some bee species spin their own cocoon inside the protective cocoon

An exposed larva, usually the larva are large and fill the nesting chamber

• A wasp larva can be surrounded by insect prey that it will eat when it wakes up again

A clear cocoon; these are fun to watch develop into adults

Wild bee cocoons identification chart

Wild Cocoons, Left to right (click the image for a larger version):

1. 8mm Mason or leafcutter type bee, used a mix of mud (walls) and leaves
2. 4mm Mason bee type, species unknown
3. 8mm Osmia coloradensis perhaps? The orange color comes from pollen
4. 8mm Waxy cocoon sent to us from the east coast, used mud for walls. Likely Trypoxylon lactitarse
5. 6mm Wild leafcutter bee
6. 8mm Grass-carrying wasp Isodontia spp, typically hunts crickets
7. 8mm Osmia lignaria for reference

Sometimes nest-building materials will be mixed and wild cocoon materials do not always match the capped ends of your filled nesting holes.

A chewed leaf looks different than a leaf bit that was left intact. Bees and wasps can also add pebbles in with the mud or chewed leaves. You might want to spend some time looking at your wild cocoons and capped ends with a magnifying glass so that you can get more information about your guests.

A wild bee larva and the thin cocoon it fell out of


Notice how chubby this larva is and how it is as long as its thin cocoon.

If you can, we recommend returning the larvae to their nesting holes and keeping the nesting hole closed. Otherwise, place the larvae into their own LeafGuardian Bag and watch for development. An exposed larva is most likely a summertime bee or a solitary wasp that will finish developing in the warmer months.


Wool carder bee cocoons showing fluff and cocoon underneath

Here is a good example of how a wild bee mother builds a protective cocoon out of gathered materials.

Wool carder bees collect plant hairs from leaves or petals, think about the soft fuzz of lamb's ear plants. Wool carder bees like to guard their fuzz sources and they prefer to nest in 8mm size holes. Within the protective cottony cocoon, the larva spins its own silky cocoon. 

There is so much to learn about our wild bees and how to raise them!