Last week I found hundreds of pure green Augochlora (Augochlora pura) foraging for pollen on Zea mays at Stroud Preserve in West Chester, Pennsylvania. Here’s my favorite capture, which shows a bee cutting open an anther with her mandibles.
I was a tad surprised to see a wind-pollinated plant so mobbed with bees, but a later search of the internet suggested I shouldn’t have been. Even honey bees forage on corn, though the pollen is apparently not as desirable as other sources (e.g., Höcherl et al. 2011). This is also the reason why spraying a cornfield with insecticides can easily cause problems for any bees (and pollen wasps) that collect pollen.
This next photographs shows a better view of the scopa (modified hairs that hold the electrostatically-charged pollen) on the legs and abdomen. It also shows off how incredibly large corn pollen is (perhaps 85 microns, per some estimates, which is huge). Wind-pollinated plants with large pollen are odd.
The final photograph shows some pollen grains set in motion by the foraging bee. The odd look (line segments with bright dot in middle) are presumably caused by the flash freezing the fast-moving grains only in the middle of the exposure (1/200 of a second). I’m not exactly sure why the grains are bright. It could be because they are strongly backlit by sun, but it could be something related to how pollen grain exines bend light (they can cause a pollen corona on allergy-alert days). Someday it might be fun to get a rear-curtain flash configured to better capture such motion.
I built a hotel for mason bees, leafcutting bees, and hole-nesting parasitic wasps and thought I’d post pics in case anybody is looking for tips on how to make one. Overall dimensions are 12″ (W) x 25″ (H) x 11″ (D) and situated facing southeast so that it catches some good morning sun (the bees like that). I gave it three levels so that I can fuss with one level without disrupting all the tenants (bees hate that), plus used dado joints give the whole structure some stability when fully loaded. The hotel is elevated to 4 feet on a 4 x 4″ post so that I can easily take photographs of the tenants without stooping.
I also have a piece of galvanized hardware cloth that can be attached (pic below), after all the holes are filled, to keep woodpeckers away. The wire is held by six neodymium magnets glued into small insets on each side. I’ll probably redo it with larger-hole chicken wire, and make it project farther away from the surface. The back of the hotel is a slab of 2×10. To attach the hotel to a post I used a small piece of wood that is first attached to the post, then attached to bottom of the house via four screws (shown below). Everything is just scrap wood from some dismantled cedar planters. Below are some pics:
There are hundreds of different bee (Megachilidae) and wasp species that nest in holes, and all have slightly different preferences for wood type, hole diameter, and depth, so I’ve offered them a variety of accommodations in reeds, logs, and milled lumber, all cut into 7-inch lengths. The reeds are from Phragmites, and each section is cut so that the end has a node, leaving approximately 6 1/2 inches of usable tube. Logs and blocks are drilled with variable sizes of bits, but most are 1/8 inch because at this time of the season there a lot of bees that like that size. The large log on bottom right also has a mix of 7/16-in and 1/8-in holes, some of which are already filled up (with mixture of nectar, mud, pebbles). Directly above the large log are two smaller ones that show how you can insert 6-in paper tubes into holes. At the end of the season you can easy pull those tubes out and transfer them to a protected location or refrigerator to overwinter. The other advantage of these disposable paper tubes is that you can easily unwind them to collect, study, and clean the pupae. The other paper tube is just a drinking straw I found on Amazon. These tubes will probably not be used this summer but I have them there just in case (the tubes are used by Spring mason bees and my house went up a bit too late this spring to attract any, I think). Finally, I have a few large-bore holes up in the attic space just in case that might appeal to a larger bee or wasp, though I probably won’t get a taker.
At the end of the season I’m going to gather up all the wood and reeds and place them in a protected location until next year. I’ll probably end up building a hatching box. After emergence ends I’ll either clean out the wood for reuse or throw it out. You need to do one or the other or risk causing diseases, mites, and parasitoids to build up in your bee house. To give you a visual on one risk, here’s a photo of a mason bee loaded up with phoretic mites. See also the Maclvor and Packer 2015 article, below.
For larger hole sizes you want at least 6 inches of depth so that bees will oviposit female eggs (i.e., mother controls sex of offspring). Bees will still use shorter holes if that’s all that’s available but it will cause them to oviposit mainly males and males are useless: bad pollinators and they don’t lay eggs. So build your shelves to accommodate 7-in lengths of reeds and logs.
To keep everything dry on something this tall you need a serious roof overhang. Mine extends 5 inches beyond the front of the shelf, plus the wood sections and reeds are set back from that by another inch or so. If you have a shorter house you can have a smaller roof.
Burning the front of the wood allows bees to more easily find their holes, plus causes the wood to heat up faster in the morning sun. Plus torches are fun to use. I got a little carried away and some blocks caught fire.
Don’t use bamboo. Bamboo (and plastic, glass, metal) is too dense and thus doesn’t allow dissipation of moisture from developing larvae. Plus it often cracks as it ages and that allows parasites to enter the brood chamber.
Don’t use treated lumber or fresh cedar. Kills the larvae, apparently.
Pine is fine but I think harder wood is preferable because the drilled holes are smoother.
Here are the tenants so far: an Osmia, several Chelostoma philadelphi, and a creepy wasp that I’d wager is a parasitoid waiting for an egg-laying opportunity.
My goals for building this house are mainly for edutainment (please join my iNaturalist project if you’re interested) but a bonus would be better pollination of my kiwi vine and strawberries. But that’s not a guaranteed because many solitary bees are oligolectic (collect pollen from only certain species of plants), and I’m not sure which species specialize on Actinidia and Frageria. I’m looking forward to next year when I can put out the blocks for (larger) spring mason bees, which I think are good for early strawberry pollination.
UPDATE: New blocks for 2019
Here’s a photograph of the fresh nesting accommodations I installed in the above hotel. Blocks have a variety of hole diameters to accommodate a variety of bee and wasp species: 3/16″, 5/16″, 5/8″, and 12mm. Hipster add-on apartment is for smaller Hymenopterans and is made from a Saint Benjamin Brewing Little White Lies IPA (design by Kathryn Moran) can packed with 5 1/2″ sections of swamp milkweed and wild begamot.