Category Archives: Gardening

Mason bee hotel

I built a hotel for mason bees, leafcutter 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 12x25x11 inches 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, plus the dado joints give the whole structure some stability when fully loaded (it’s, um, a tad heavy). The hotel is elevated to 4 feet on a 4×4 post so that I can easily take photographs of the tenants without stooping.

Mason bee hotel

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.

There are hundreds of different bee (Megachilidae) and wasp species that use 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. Half of the 2x4s have 3-in deep holes and half have 5-in deep holes (I’m interested in whether bees Phragmites culms for mason beeshave a preference). 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).Drilling holes for mason bee inserts 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.

Some design considerations

  1. 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.
  2. 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.
  3. 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.
  4. 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.
  5. Don’t use treated lumber or fresh cedar. Kills the larvae, apparently.
  6. Pine is fine but I think harder wood is preferable because the drilled holes are smoother.

If you need inspiration there are thousands of mason bee house designs on Pinterest.

Guest list

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.

Further reading

Tricrania sanguinipennis, a bee parasitoid

Found this striking, highly punctate beetle in my yard a few days ago and finally figured out what it is: Tricrania sanguinipennis, a blister beetle (Meloidae). Apparently a parasitoid of Colletes spp., ground-nesting bees that are often situated in dense aggregations. I have hundreds of digger bees in my front yard each year, so I’m guessing that some or all are Colletes, but I’m trying to confirm (casual guess is C. inaequalis, the unequal cellophane bee).

Colin Purrington Photography: Insects &emdash; Tricrania sanguinipennis

Per Parker and Böving 1924, female T. sanguinipennis deposit clumps of eggs near these aggregations and when larvae hatch they seek out adult bees and clamp onto body hairs with specialized mandibles. If the bee happens to be a female, larvae release their grip when she arrives at the brood cell, sometimes up to 2 1/2 feet underground. If the beetle larva has attached to a male bee it will move onto a female while the bees are mating. Once in the nesting chamber the larva will seek out the bee egg, eat it, then set up camp inside the cell (see fig 21, below) that holds the honey and pollen, which it will eat until maturity.

Below is Plate 3 from the Parker and Böving article. If you expand the image you can see that the bee has multiple larvae attached. I think I might need to capture a few of the bees this Spring to see whether I can find some of these hitchhikers. Am also trying to find the egg clumps, which can have thousands of eggs. That’s a lot of eggs for a beetle but the success rate of the larvae must be extremely small so they’ve presumably evolved large brood size to ensure that at least some find their way into a nest.

Tricrania sanguinipennis

Illustrations of Tricrania sanguinipennis larvae from Parker and Böving 1924.

Very cool beetle and just had to share the find. If you’d like to see more photographs, there are currently 27 sightings Tricrania sanguinipennis on iNaturalist. I highly recommend the Parker and Böving article for the biology details but mainly for how they figured out the details; it’s hard to figure these things out when the species spends its life underground. For more information on related beetles this page by Dr E. F. Legner (UC Riverside) is excellent.

Exobasidium ferrugineae

I found this fleshy, flower-like structure growing on Lyonia ferruginea (rusty staggerbush) at Archbold Biological Station (Venus, Florida). Heaths don’t make flowers like this, so I originally thought it might be an insect gall or phytoplasma infection, but I was wrong. After poking around online I think it’s Exobasidium ferrugineae, a Basidiomycetes fungus. Members of the genus grow in between cells of flower and leaf tissue, then in the Spring send hymenial tissue through stomata and other cracks in the epidermis, eventually turning the surface white with spores. I’d never heard of such fungi before. I’ve led a sheltered life.

Colin Purrington Photography: Fungi &emdash; Exobasidium ferruginea on rusty staggerbush (Lyonia ferruginea)

The above was the largest structure I found (perhaps 3 inches high) but there were dozens of others (see below) at the same location. If you’d like to know more about the species and genus, a good starting point is Kennedy et al. 2012 and references therein. In older literature the fungus was known as Exobasidium vaccinii (Burt 1915), but it seems likely that that species is host specific to Vaccinium vitis-idaea.