Some photographs of Chelostoma philadelphi, the most common guest at my mason bee hotel in past years. Approximately 7 mm in length and all black unless covered in pollen. Seems to prefer nest holes that are 1/8″ in diameter. In looking at photographs online they seem to show up on a variety of flowers (perhaps with preference for asters), but females are reported (Sedivy et al. 2008) to collect only Philadelphus pollen for use in nest provisions for her brood.
Here are some of the pics I’ve taken at bee hotels over the past several years. Sharing in case other beekeepers might recognize residents in their own hotels. There were bees, as one would expect, but also wasps, flies, and beetles.
Horn-faced mason bee (Osmia cornifrons). Very common at my hotels. Introduced from Asia in the 1970s. Details at BugGuide.
Taurus mason bee (Osmia taurus) are also common and also introduced. Details at BugGuide.
Giant resin bee (Megachile sculpturalis). Yes, also introduced, though more recently (~1994). Details at BugGuide.
Mock-orange scissor bee (Chelostoma philadelphi). So named because it prefers to collect pollen from trees in the genus Philadelphus (mock oranges). This is the only native member of the genus in the United States. Details at BugGuide.
Ancistrocerus antilope has shown up a few times at my hotels, but apparently prefers to nest in sumac and elder stems. It also is reported to use old mud-dauber nests. They are fun to watch because they provision nests with caterpillars. Details at BugGuide.
This is Euodynerus “Species F” at the moment. I.e., it’s one of several undescribed species in the genus (details here). Its biology is apparently unknown, so I’m hoping to get more of them in the future.
Parancistrocerus histrio is another wasp that feeds caterpillars to its brood. Details at BugGuide.
Euodynerus megaera is extremely similar to the above species but has black tibiae. At least females do (males are much harder to distinguish). It’s also a collector of caterpillars. More details by Buck et al.
Brown-legged grass-carrying wasp (Isodontia auripes) provision their nests with tree crickets. As their name suggests, they also carry grass, which they use to pack and seal the brood chamber. Details on BugGuide.
Here’s a photo of the grass-carrying wasp’s nesting plug that I took at Longwood Gardens. They have a beautiful bee hotel with hundreds of cells but as far as I could tell, only a few wasps had moved in.
Trypoxylon collinum provision their nests with spiders. Unlike many wasps and bees, the males in this genus actually help out around the nest. For details, please see this Instagram post. BugGuide has a page for the species but it contains little information.
Cuckoo wasp (Chrysis sp.). They are absolutely adorable. That said, they are also parasites of the above bees and wasps that are nesting at the hotel. They are very difficult to identify, so even getting them down to genus is rare. Here’s BugGuide’s page on the family.
The club-horned cuckoo wasp (Sapyga louisi) is another frequent parasitic wasp at my hotels. This one is patiently waiting to gain entrance to the nest of a mock-orange scissor bee. Details on BugGuide.
Monodontomerus sp. (in Chalcidoidea) are extremely common parasites of mason bees. Please see this post at Nurturing Nature for great video and description of their life cycle. Additional details at BugGuide.
Digonogastra sp. These braconid wasps are parasites, but I’m not positive the ones I’ve seen at my bee hotels are targeting any of the residents. But they’ve shown up on at least two occasions so I think it’s a possibility.
Amobia sp. are flesh flies that develop on the provisions inside (for example) Trypoxylon nests. I’m not sure whether the larvae also eat the wasp larvae, but I’d suspect so. Details at BugGuide.
Houdini flies (Cacoxenus indagator) are newly introduced to the United States and are likely to ravage mason bee nests and the crops that depend on them for pollination. If you have bee hotel, this fly is reason #1 why you should use removable paper tubes that allow sorting of infested and uninfested brood cells. Without paper tubes your bee hotel will likely be a Houdini fly hotel. Crown Bees has information on how to clean your tubes.
Skin beetles (Dermestidae) are scavengers but can become serious pests of uncleaned mason bee hotels. Yet another reason to use only paper tubes fitted inside drilled holes, combined with a thorough cleaning of entire hotel (e.g., soak in bleach, scrub). Details on skin beetles at BugGuide.
The above is probably less than 1% of the species that might be found at a bee hotel that had a range of nesting-hole diameters. Noticeably absent are leaf-cutter bees, so that’s my photo resolution for 2021.
Note that almost everyone calls these hotels “bee hotels”, but in my experience the majority of the residents are wasps. That’s totally fine with me. Wasps are pollinators, too. And wasps tend to be more photogenic and possess more interesting life histories if you ask me. In related news, I’m really looking forward to reading Heather Holm’s new book, Wasps: Their Biology, Diversity, and Role As Beneficial Insects and Pollinators of Native Plants.
For my full collection of photos at bee and wasp hotels, please click on button below.
In nature, tunnel-nesting bees are perfectly happy to use logs riddled by boring beetles or piles of dead plants that have hollow stems. That habitat is often in short supply in many yards, however, so it’s necessary to provide hotels if you want to attract them. These hotels can be as simple as a large coffee can filled with hollow reeds … or as elaborate as the three-level one I built. The bees really don’t care.
Types of nesting material
DIY bee hotels can be filled with routered nesting trays (you can buy these or make your own, if you’re handy), wood blocks with paper inserts (these inserts can be purchased), wood blocks or logs with drilled holes (unlined), or just sections of hollow stems (by far the easiest). Or, like house in the photo below, a mix. A hotel should have a roof to keep the tunnel entrances relatively dry, should be situated to get morning sun, and be approximately 5 feet off the ground (so you can enjoy watching them).
Below is a photograph of my other hotel. It’s smaller and is set up in my front yard to entertain people who walk by. Tunnels are all unlined drilled holes, plus milkweed stems. Holes in the blocks are varied because I want to attract a variety of solitary bees.
Swap nesting materials regularly
The ideal bee hotel is one that allows all the nesting material to be removed each year (or so). By installing fresh nesting material, new tenants each spring will get to move into tunnels free of kleptoparasitic pollen mites and pathogenic fungi. Another benefit of removable nests is that you can remove sections as they get filled, allowing you to replace the spot with the same type of tunnels or with tunnels that have different diameter to cater to a different bee species (there are hundreds). Below are examples of my hotel with different configurations (my 2020 version, on right, is a bit boring).
What do you do with the nesting material after you remove it from the hotel? I put mine into a large cardboard box that has holes in the sides and at the top, then store in my unheated garage for the winter. In mid March (before bees in my area start to wake up) I put the box outside in a spot that is dry and gets good morning sun. Then when bees emerge from their cocoons they can escape from the box but are disinclined to re-inhabit the nesting tunnels they emerged from. Here’s a view of the nesting material inside my emergence box.
After several months outside (e.g., in August, long after the last resident has emerged) I take everything back into my shop and redrill holes and sterilize the wood. Then I can reuse blocks in future years.
Lately, I’ve been thinking that I should move entirely to a system where I can sort through pupae at the end of the season. E.g., as summarized here. The reason for this is that I’d like to remove (kill) the kleptoparasitic mites (pic) and Houdini flies (pic) that are likely destroying many of my solitary bees. To enable this process I am going to start using paper straws to line all the tunnels. These straws can then be removed and unwrapped and the contents examined. Below is a photograph showing how drilled holes can be lined with paper straws — just fold over the back overhang and seal with foil tape.
Several companies sell sturdy (and easy to unwrap) paper straws as well as cardboard tubes that can easily accommodate the straws (i.e., you don’t need to drill holes in wood).
Another way to sort through pupae is to use routered wood trays, which you can buy or make (with a router or a table saw). Although some types of trays are better used with straws (to prevent mites from moving from tunnel to tunnel), others fit snuggly enough to be used without them. On my list of things to do is to make some routered nests that are sealed on one side with Plexiglas so that I can observe the bees within (such hotels can be purchased, and are beautiful).
- To keep everything dry on something this tall you need a generous 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.
- For larger hole sizes you want, ideally, 6 inches of depth. Shorter (4″) tunnels are fine but can result in a male-biased brood sex ratios. If you want to encourage population growth, encouraging the production of females is important. So buy long bits (I really like my 5/16″ auger bit, shown in drill below).
- Burning the front of the wood allows bees to more easily find their holes, plus the darker surface causes the wood to heat up faster in the morning sun.
- Avoid treated lumber or fresh cedar. Per rumors on the internet, those types of wood can result in the death of the larvae. Pine is fine but I think harder wood is preferable because the drilled holes tend to be smoother.
- For cutting reeds to size, I highly recommend using a cutoff disc on a Dremel tool instead of pruners. You can get a really smooth surface with a Dremel.
Examples of nice DIY solitary bee hotels
- Anonymous (nicely routered nesting trays)
- Jordan Arata (beautifully-made observation house)
- Jason Chrisman (video how-to for simple blocks w/ parchment paper liners)
- Marc Carlton (plus excellent maintenance tips)
- Linda Chapman’s hubby
- Jan Cordell
- Emily Doorish (you should follow her on Instagram & Twitter)
- Horticultural Centre of the Pacific
- Gord Hutchings (plus good overview of biology)
- Tricia Hogbin (use of cinder blocks is great)
- Lakeside Gardens (tad large but I love public displays of bee affection)
- Joe Larson
- Ed Marshall (NB: screening keeps birds from eating larvae)
- NestBoxTech (plus great instructions, links)
- Pavel (really well engineered)
- Ed Phillips (elegant array of blocks with nice hole diversity; see also this)
- Place des Jardins (trés jolie mais trop grande, je pense)
- Axel Reuter
- Mark Smith
- University of Nebraska Extension (great PDF on topic)
- Bauer, E.C., L.I. Lynch, D.A. Golick, and T.J. Weissling. 2015. Creating a solitary bee hotel.
- Carlton, M. 2017. How to make and manage a bee hotel: instructions that really work.
- Edmunds, B., R. Little, and R. Sagili. 2016. Nurturing mason bees in your backyard in Western Oregon.
- Farmer, C. Leafcutter bee nests.
- Green, A. Checking into bee hotels.
- Hunter, D., and J. Lightner. 2016. Mason Bee Revolution: How the Hardest Working Bee Can Save the World – One Backyard at a Time.
- Krombein, K.V. 1967. Trap-nesting Wasps and Bees: Life Histories, Nests, and Associates.
- Maclvor, J.S. 2017. Cavity-nest boxes for solitary bees: a century of design and research. Apidologie 48:311-327.
- Maclvor, J.S., and L. Packer. 2015. ‘Bee hotels’ as tools for native pollinator conservation: a premature verdict? PLoS ONE 10:e0122126.
- Mader, E., M. Shepherd, M. Vaughan, and J. Guisse. Tunnel nests for natives bees: nest construction and management.
- McGlynn, D. 2009. Backyard boarding house: how a power drill can attract pollinators.
- Moon(?), C. How to make solitary bee houses.
- Morato, E.F., and R.P. Martins. 2006. An overview of proximate factors affecting the nesting behavior of solitary wasps and bees (Hymenoptera: Aculeata) in preexisting cavities in wood. Neotropical Entomology 35:285-298.
- Nye, W.P. and G.E. Bohart. 1964. Equipment for making nesting holes for the alfalfa leaf-cutting bee.
- O’Neill, K., and J.F. O’Neill. 2013. Cavity-nesting wasps and bees (Hymenoptera) of Central New York State: the Roy H. Park Preserve and Dorothy Mcilroy Bird Sanctuary. Proceedings of the Entomological Society of Washington 115:158-166.
- Palmer, D. 2017. Adventures of an amateur mason bee keeper.
- Phillips, E. Wasps in the bee hotel!
- Seidelmann, K., A. Bienasch, and F. Pröhl. 2015. The impact of nest tube dimensions on reproduction parameters in a cavity nesting solitary bee, Osmia bicornis (Hymenoptera: Megachilidae). Apidologie 47:114-122.
- Tei-Weisenburger, J-L. 2017. Insect hotels: a refuge or a fad?
- Werner, D. Schautafeln zum Thema Insektennisthilfen und Wildbienen.
- Werner, D. Fertig zum Einzug: Nisthilfen für Wildbienen.
- Wilson, J., and O. Messinger Carrill. 2015. The Bees in Your Backyard: a Guide to North America’s Bees.
- Xerces Society. 2009. Tunnel nests for native bees: nest construction and management.