Friday 5: Leafcutter Bee Nest Caps

The bee house I put up in my yard in mid-April has been a complete success!  Nearly every cavity has been filled with nesting materials and eggs and now I’m waiting for the new bees to emerge.  I’ve watched them obsessively and am keeping hard-core notes about the whole process, so I am totally in love with my bees!  One thing that has fascinated me is the variety in the capping stuctures and materials used among cavities.  To the best of my knowledge, all of my bees are these:


A leafcutter bee (Megachile) bee making a nest

They’re a species of leafcutter bee in the genus Megachile.  Even though they’re apparently all the same species, they’re still building their nests according to… something!  Maybe it’s individual preferences or access to the building materials that controls it, but three different caps might be built by three different bees on the same day.  Fascinating!  My bees have been spending 2-3 days busily building their nests and laying eggs and then spend part of a day building a cap to seal everything safely inside.  They’ve made 5 different types of caps so far, perfect for Friday 5!

Resin Caps

resin cap

Resin caps

The first several bees made these caps.  Then they stopped making them.  Most recently, bees have been STEALING the resin from the completed resin caps, cutting pieces away from the caps and hauling them off, and then recapping the nests with mud.  Odd!  I assume there’s a resin shortage now and they’re scrambling to find it wherever they can.  When the bees build this kind of cap, they bring big globs of it from somewhere on the other side of my house, then stretch it across the opening.  (The bee in the photo at the top has a big glob of it in her jaws, ready to stick it onto the cap.)  Then they pile a bunch more on the front, making a thick, flexible cap.  They smell awesome too!  You can smell the resin from several feet away.  Reminds me of vacations in the pine topped mountains in Colorado…

Leaf Caps

Chewed leaf cap

Leaf cap, in progress. (This one is still green, even though it's now dry.)

Some of the caps, though not many, are made of chewed leaf bits.  The bees bring in large pieces of leaves or flower petals or other plant materials, then chew them up and stick them onto the nest.  Presumably they are sticking the leaf fragments together with saliva.  The best thing about the leaf caps is the variation in color!  Most of them are green like this one, but I have one yellow, one purple, and one vivid red one too.  Awesome!

Rock Caps

Rock cap

Rock cap

These seem to be the least popular choice, but there are a few.  The bees use resin to attach little pebbles (which they collect from the corner of my yard) onto the front of their nests.  After they build up a few layers of rocks, they call it good and either start a new nest in another hole or fly away.  I love watching the bees make these caps!  There’s something about a bee flying around with a rock nearly the size of her head clamped in her mouth that is both inspiring and terribly entertaining.

Flat Mud Caps

Flat mud cap

Flat mud cap

The mud caps are very popular with the bees in my bee house and they take one of two forms.  The flat mud caps are built so that the outer edge is flush with the face of the log in which the cavity is located.  After they dry a bit, they tend to sink inward in the middle a little, giving them a gentle concave look.  To the best of my knowledge, the bees are making the mud themselves by carrying little piles of dirt from another part of my yard, mixing it with saliva and chewed leaf bits, and then spreading the whole mess across the nest entrances.

Round Mud Caps

Round mud cap

Round mud cap

This was the last style of cap to appear in my bee house, but they look really fabulous!  The round mud caps are a sort of mixture of the flat mud cap and the rocks cap.  The bees stick a bunch of little rocks onto the front of the nest, building out past the edge of the log.  Then they plaster over the whole thing with mud as in the flat mud cap.  The result is a cap that extends well beyond the nest entrance, almost like the little developing bees inside are blowing bubbles in the mud!

Watching my bees has been great and I’m very pleased my bee house has worked as well as it has.  And just look at all the individual choices being made by the bees!  Fabulous.  I’m definitely going to make myself some new bee houses (even bought a new power tool – my first circular saw – to do it!) because it’s been great fun watching them build their nests.  I highly recommend the experience!


I am going to do my best to get a blog post up on Monday, but there’s a good chance it won’t happen.  I am leaving town for a family emergency today and that is a lot more important than getting a blog post out on time.  I will be back, and as soon as I can, but if you don’t hear from me for a while that’s why.


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3 thoughts on “Friday 5: Leafcutter Bee Nest Caps

  1. Perfect timing! I was trying to figure out what was going on in my kids play shed. There is an old series of hooks that broke off (I wonder how that might have happened- hint, kids), and left holes in the wood. I saw a bee-like creature coming out of one of them a couple of weeks ago, and I now notice that the holes are all filled with mud! I guess we’ll have new bees soon?

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