Bummer. Whether it can be saved is a tough call. I guess it depends on their state of development. After the mason bee larvae eat what mom left for them they spin a hard cocoon and metamorphose inside. If the cocoon is completely formed you might could rescue them. Best to ask someone in your zone what state of development they may be in at this time. A local expert is what you need…
If it’s the monodontomerus wasp, it parasitizes the pupa inside the cocoon
I’m just going to let nature take it’s course here I guess. I’ve seen some people say they put a screen over the house so that wasps can’t get in? I guess I need to figure out what time of year would be best to do that. I let wild bees nest in my house- I’ve never bought them in. I’m not sure when they’re done laying.
Usually, the first of July is recommended
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Thank you, appreciate the info
I bought 4 Mason bee “houses” a few years back. I have not put them out for a few reasons. I had Mason bees nesting in some wrinkle black plastic bags under my carports. I am just going to put them out next year just to see if I can get them to come nest in those “houses” without putting covers on the front of them. It is like an outside down teardrop shape filled with tubes. I like the idea of them pollinating my fruit trees but I hate the idea of having to buy, store, and replenish the bees every year. I hopefully will get the ones around her to use the tubes I will have available.
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I don’t buy new bees or tubes. I do check on the houses. Squirrels will get in them to eat the eggs.
John S
PDX OR
Squirrels eat the Mason bee eggs? I never knew that.
so will the woodpeckers. i remove the tubes in late summer then store them in the garage till late fall. then i split the tubes and harvest the cocoons to store in tupperware , in the fridge, until spring. when the willows wake up, i put them out in a coffee can w/ a small hole drilled in the lid, taped to the top of my mason house. fun to see them sitting on the coffee can warming themselves in the sun. they can be handled if you’re gentle.
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The hibernating young bees
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Those squirrle’s are like goats, they seem to eat everything.
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Update on year 2 of Mason bee keeping… I put out 19 cocoons this past spring that I had collected in dec 2017. Yesterday I collected 118 cocoons. Would have had more but had some worms in some of the tubes that seemed to have eaten the masons. If I get another 6 fold increase next year I will have all I can handle. That seems like a high reproductive rate, but i guess for an insect maybe on the low end. The kiddos are having fun with it.
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My Mason bees have been a complete waste of time and money. I pulled my house and opened it a few weeks ago and I didn’t have a single cacoon. I’m not sure what happened. I had some of the holes capped off. My 40-50 bees that I ordered 2 years ago are effectively zero now.
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So I’m mulling over a design to house the mason bee blocks next spring (another winter project) and would appreciate a few more eyes on it. It isn’t elaborate or expensive by any measure, but I may be missing something which may result in missing bees. I plan to use a 5 gal bucket to set the blocks in so that I can protect them from known predators. I’ve read that some birds will hang around their mud sources to pick them off so I also put the mud inside the bucket also protected by chicken wire. Whatcha think?
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I like what you designed and it is obvious a lot of thought when into the planning. This question is from someone who knows very little about mason bees. The block appears to be in the back section of the bucket and I’m wondering if the bee will go there to deposit their eggs.
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I’ve found that even if no mud was put out,they still discovered it somewhere.bb
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Well I am a newbie at this, but I tend to read everything I can before I feel I have enough to begin and avoid bad most outcomes - at least the bad outcomes others have reported. 
Allegedly if you release the bees from the site where you want them to nest and use a pheromone on the block, they will be attracted back to that site to nest. Other folks have used this approach successfully, so we’ll see. The deep set is only 8" and allows room for the mud container.
@Bradybb We live near a creek bed so there is plenty of mud for sure, but some folks have reported that whilst the mason bees collect their mud, the birds pick them off. So it is not a supply issue but rather a protection measure to have mud inside the chicken wire. If I had lots of bees, I wouldn’t be as concerned, but until I am able to build up a sizeable colony, I want avoid as many pitfalls as I can. 
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I’m going to give masons a try this year for the first time, so this isn’t a response from actual experience, but if your bucket house gets any sun I wonder if you may have a heat issue in the bucket even with the holes drilled in the back. Not so much just the heating of the house/tubes themselves, but on calm days the air temperatures in the bucket could be significantly higher and the house/tubes could stay warmer later in the day without the cooling effect of breeze/cooler air directly against it. It might effect whether the bees would choose to use it for nesting, but might also effect the development of the larva.
If you try it, I would definitely use a white bucket and maybe do one in a bucket and one without and see which they prefer using. You could see if the bees show a preference for which they use as well as if there is any difference in development/survival of the next generation. Of course so many other things can effect the bees, it may be hard to know for sure what is working best without years of testing…
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That’s a good point zendog.
Also,there are usually no kinds of bees flying around,when the Plum trees flower here,because it’s too cold.Masons are active,primarily with the Blackberries and Blueberries.
With something like Anne’s bucket,that could be mobile and be placed in an area,either sunny or shady,so that their emergence coincides with the target bloom.It might be kind of tricky,just something that could be experimented with. bb
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I use an old black plastic mailbox to keep my bee houses in, leaving the door open. Haven’t had problems.
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