Tag Archives: parasites

Sorting through guests at my insect hotels

When the weather is cold and rainy in winter, I entertain myself by bringing the nests from my bee and wasp hotels inside for photo ops and cleaning. With a hot cup of tea (I’m in a cold basement), I carefully open up all the occupied nesting tunnels, then put the cocoons and larvae into vials so I can see who eventually hatches out in the spring. Here’s my set-up before I made a complete mess:

Removing the paper liners (here, straws from a local supermarket) from the nesting blocks is much easier with a pair of forceps. The blocks are necessary because if I just crammed paper straws into my bee hotel, every single nest would be parasitized by wasps that could easily get access to the larvae along the length of every straw.

Below are the cocoons of a mason bee, separated by mud plugs and covered with frass. They are probably Osmia cornifrons (pic of adult) or Osmia taurus (pic of adult), both introduced species that are frequent visitors at my hotels. Unwrapping the straws is usually pretty easy, but sometimes you need to use the forceps to grab onto the edges to complete the job.

I also had two stems filled with Georgia mason bees (Osmia georgica), a native species that has a beautiful blue body (pic of adult). It has smaller, bright orange frass and uses chewed plants to seal partitions. It also smells different.

Below is a visual reminder of why I need to sort through my nests each year: Houdini flies (Cacoxenus indagator). These kleptoparasitic dipterans eat the pollen balls that mason bees feed on, resulting in the death of the bee. So when I find them send them along to fly heaven. The common name is from their ability to bust open the mud plugs (they have inflatable heads for the job). Here’s a pic of an adult.

I also had grass-carrying wasps move into the observation panel, below, that I built a few years ago. There’s one nest near the top, and one at the very bottom, possibly provisioned by the same female. Because this panel slides in and out of the hotel easily, I was able to get a photographs of the adult, an egg, and a larva last year.

Here’s a close-up of the cocoon from the panel. It’s quite large. A photograph of a cleaned-up cocoon from a previous year is on my iNaturalist account if you want a better view. If you have a good eye, you might be able to make out a book louse (Liposcelis sp.) on the left-hand side of the cocoon. Here’s a close-up from a previous season if you’re curious.

One of my bee hotels is packed full of hollow stems, so for these I use a knife to split them open. Here’s a brood of potter wasps inside one of them. I’m not sure what species they are (or even genus) but I’ll know in several months when they hatch and I can get an identification on iNaturalist. And there’s a possibility that one or more of the larvae is harboring an internal parasite, too. Or at least that’s what happened in a previous year, when a beetle appeared (see my post about it). A beetle parasitizing one of my wasps was not on my Bingo card that year. I love surprises like that.

In the smaller stems I get lots of these cocoons, likely Trypoxylon collinum (pic of adult), a charming little wasp that feeds very small spiders to its young.

Although I enjoy looking through the nesting tubes, the main reason I do it is to make sure I’m not just breeding Houdini flies, pollen mites (pic), and pathogens that could easily spill out into bee and wasp populations near my house. I.e., if during my cleanings I felt that I was doing more harm than good to local native species, I’d shutter my hotels and find alternate entertainment.

As you may have noticed during the above, I love wasps. So if you have a bee hotel and get wasps, that’s a bonus, not a problem. And thus I implore everyone to not kill the larvae and the pupae simply because they are not mason bees. They both pollinate plants, plus wasps are fantastic at patrolling your vegetable gardens for pests, which they take back to their nests to feed to their young. If you’re on the fence about wasps, consider treating yourself to book on their biology and identification. I have Heather Holm’s fantastic Wasps: A Guide for Eastern North America. I’ve also heard great things about Eric Eaton’s Wasps: The Astonishing Diversity of a Misunderstood Insect and Seirian Sumner’s Endless Forms: The Secret World of Wasps.

More information

Below are my other posts about insect hotels if you want to learn more. If you have a question, send me an email via my Contact page.

Gallery of bee hotel visitors

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)

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)

Taurus mason bee (Osmia taurus) are also common and also introduced. Details at BugGuide.

Giant resin bee (Megachile sculpturalis)

Giant resin bee (Megachile sculpturalis). Yes, also introduced, though more recently (~1994). Details at BugGuide.

Mock-orange scissor bee (Chelostoma philadelphi)

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

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.

Euodynerus "Species F"

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

Parancistrocerus histrio is another wasp that feeds caterpillars to its brood. Details at BugGuide.

Auplopus mellipes

Auplopus mellipes provisions its nests with spiders. For a wonderful overview of their biology, please see post on Eric Eaton’s blog. (While there, I noticed he has a new book on wasps.)

Euodynerus schwarzi

Euodynerus schwarzi provisions nests with caterpillars. For identification tips, see blurb by Matthias Buck et al.; more pics are at BugGuide.

Euodynerus megaera

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)

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.

Grass-carrying wasp (Isodontia sp.)

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

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.)

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.

club-horned cuckoo wasp (Sapyga louisi)

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.

Leucospis affinis

Leucospis affinis is another parasitic wasp that is almost always lurking around my bee hotel. It’s oddly variable in size. More details by Ari Grele at Insects of Cornell, at BugEric, and BugGuide.

Monodontomerus

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.

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

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 fly (Cacoxenus indagator)

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 beetle (Dermestidae)

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.