Hymenoptera Hotel

In 2010, inspired by my botany-bud Paul, I built and hung my first backyard bee block.

What's a "bee block," you say?

It's a hand-made habitat hotel for native bees, of course.


My new bee block on the wall right after I hung it

You see, many of the native bees in CA use such small holes in wood or soil for their nests and overwintering egg chambers. The classic big black California Carpenter bees that over-love our patio posts and rafters being the most well-known, I expect.

My block saw very little use the first season. But, by season 2, the native bees had found it, and started moving in. I've seen several species on and around the block so far, but the most common residents, and the least camera shy, are the too-cute little leafcutter bees.


Leafcutter bee, likely Megachile brevis, the Short Leafcutter, chillin' by her hole


Leafcutters working hard on Labor Day to finish up their nests


One taking a break after collecting pollen to prime her nest's cells


Another bringing in a flower petal to line the walls of the cells


Capping a nest


Six capped nests showing leaves, petals and mud as building materials


Some even like colorful caps, such as this one made from Cal poppy petals

Now, as we near the end of season 3, the block is pretty much full.

And not because I've kept mortgage rates low. It's full up because successive generations of bees generally come back to where they were born to build their own nests.

However, the bees aren't the only visitors to the block. As with most animal species, where there's herbivores, there's carnivores. In this case, parasitic wasps...


A Black and Yellow Mud Dauber hunting for spiders to parasitize for her children


And another spider hunter sniffing around


A tiny Torymid Wasp, likely Torymus californicus, looking for oak gall wasp galls to parasitize (I have 2 small oak trees in my backyard too)

But, the most interesting visitor to the block by far has been Lady Leuco - a parasitic Leucospidid wasp that is commonly associated with Megachile brevis. I.e, the cheetah to the gazelle.


Leucospidid Wasp, likely Leucospis affinis, sniffing around the block


Looks a lot like a yellow-jacket, huh? She's a mimic. She even flies like a hornet in that zig-zaggy back-and-forth manner. But, she's about 2/3 the size, and has no stinger - her collapsible backside is just full of ovipositor and eggs

Nicely, her repeated returns allowed me to bust out my macro lens for a few rounds. Nothing like the masters at Beetles in The Bush, but definitely some of my best of such a small subject.


Lady Leuco sniffing for full leafcutter bee nests. When she finds a spot she likes, she drums her butt on the wood to precisely echolocate a cell


Macro shot of the junk in her trunk as she unfolds it to drill


Ovipositing her eggs into the leafcutter bee egg chamber. It's amazing how easily she's able to push that needle (her ovipositor) through the wood


Drill baby, drill! A terrific aspect of these Lady Leucos - once they're ovipositing, they'll sit still and let you stick your lens all up in their face

Now, some might say that by creating such a focal point, I could be hurting the native bees by allowing them to be parasitized more easily. But, I'm dubious of that. The evidence just doesn't seem to support the idea. I see many more leafcutter bees in my backyard than I did pre-block. I.e., I think the increase in leafcutter proclivity from having access to ideal egg-chambering habitat is outpacing any parasitism. Probable reasons why:

• leafcutter bees produce multiple generations per year
• a chamber can have multiple cells, back-to-front, with an egg in each
• the first thing the hatched Leucospis larva does is kill any other Leuco larva or eggs in the cell to eliminate the competition
• each Leuco larva only parasitizes 1 leafcutter larva

Making a bee block is easy, btw. If your kids are aspiring nature geeks, or you just want to support and observe some cool native bees+, you might want to give one a go. Get a chunk of wood, drill some holes into it, and mount it solidly in a sunny spot. Don't use redwood - a lot of bees don't like it. I used a fir 4x4, but natural logs work great, too. You can drill various sized holes to attract different kinds of bees - I ranged from 1/8" to 5/16" and kept them all roughly 2" deep. Just don't drill through the wood, or they'll have to plug both ends.

Btw - supporting native bees is great for the garden, too. Especially if you grow any native wildflowers. European honey bees don't like/know all of our native flora, so the native bees help cover the gaps and can increase fruiting and the reseeding of annuals.

Oh - and the sweet little Megachile leafcutters seem to prefer the 3/16" holes. :)

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References:

• Charles Duncan Michener - The Social Behavior of Bees: A Comparative Study
• Charles Duncan Michener - The Biology of Leafcutter Bees
• Jerry A. Powell and Charles L. Hogue - California Insects
• BugGuide - Megachile brevis
• BugGuide - Leucospis affinis
• Earthlife.net - An Introduction to the Solitary Bees
• Wikipedia - Leucospidae

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