Mason Bee Pests?
I have a bee house for mason bees located in my butterfly garden. Over the last 3 to 4 weeks, bees laid eggs in 9 of the bamboo tubes and sealed them closed with mud. To my surprise and dismay, when I went to check on them today, I found the tubes open and empty. Is this a sign of mason bee predators invading the nests? If so, what types of predators might I be dealing with and how can I protect the nests from these predators in the future?
Midland County Michigan bees
I checked with my colleague, Dr. Kelsey Graham, (https://www.canr.msu.edu/people/kelsey_graham). Here is a summary of her response:
You could have parasitic wasps or, more likely, mason wasps. Mason wasp nests look similar to Osmia nests. (They have a mud cap on the end). Mason wasps have at least 2 generations each summer, and they can emerge pretty fast.
Dr. Graham said that having mason wasps isn't a cause for concern. It's natural that mason wasps would move in, and wasps can help with garden pest control. (For example, they provision their nests with caterpillars.) Mason wasps are also solitary and therefore pretty friendly.
Dr. Graham also suspects that bamboo nests might be particularly attractive to mason wasps. Perhaps switching to another nesting material (paper tubes or wood blocks) would encourage more bees.