Cavity Nesting Solitary Bees (and Wasps)
30% of native solitary bees make their nests in old beetle tunnels in dead trees. These same bees will be attracted to artificial bee houses that provide a similar habitat.
Solitary bees and wasps do not have a queen, each and every individual female lays her own eggs. Species that lay their eggs in wood tunnels look for a hole of suitable size and length to lay eggs. The perfect hole size for mason bees, to include the blue orchard bee and its non-native counterpart the hornfaced bee, is a hole diameter of 5/16″ in diameter and six inches in deep. Female eggs are laid first, than male eggs. If the hole is to shallow, fewer female off spring will be produced. In addition to bees, some native solitary wasps will also take advantage of this habitat.
Bees that will be attracted to your bee house include: mason bee (blue orchard bee), wool carder bee, leaf cutter bee and potter wasps. None of your new residents will sting you. All are docile non-aggressive bees.
There are a number of ways to create habitat for cavity nesting bees. In all cases make sure that the nests are in a dry sunny location protected from the worst weather. Sunny southern exposures make better nest sites as the larvae will spend the winter in these tubes and emerge in the spring.
1) Drill holes in existing tree snags, stumps, logs, fenceposts or other wooden areas in your backyard. Holes should range between 3/32″ and 3/8″ and be closed at one end. The smaller holes do not need to be as deep as smaller bees require less space.
2) Purchase an already constructed nest box with replaceable tubes. Paper tubes are easily replaced so bees do not reuse the same holes that could spread disease.
3) Cut raspberry or blackberry stems in the winter as these will make ideal homes for small carpenter bees and some types of sweat bees in the spring.
4) Create stem and tube bundles about 6 to 8″ in length of plants that are naturally hollow such as teasel, bamboo, reeds, sumac and even brambles such as blackberry or raspberry (perfect for the small carpenter bee). The stems should be cut as close to stem nodes as possible to ensure a closed end.
Bumble Bee Houses
Bumble bees are social bees and have a hive with a queen, workers and drones. Bumble bees queens are not too picky as to where they choose to live and typically live in an old mouse nest or under a grass tussock. A simple box can make a perfect shelter for bumblebees. These boxes can be placed on the ground in a shady area.
Artificial nest boxes have a low occupancy rate of less than 30%. So having a few boxes will increase the odds that queen bee will select a box as her nest site. They should be put in place very late in the winter or very early in the spring to increase the odds that a emerging queen will find a nest site ready at the time of her search.
I have concern for recommending bee blocks, bundles, “bee hotels”. Entomologists at the The CT Agricultural Station in New Haven, CT share my concern. These structures are not a natural nesting habitat for bees or wasps. The general consensus by the CTAg Station and the Xerces Society is that natural habitat is best. Natural cavities such as logs, snags, hollow-stemmed plants and canes are the very best habitat and should be encouraged. Often what we humans do to “help” is the wrong thing and may actually be detrimental. Disease and parasitism can be spread when nesting is in close proximity. Birds such as woodpeckers find an easy snack and parasitic insects take a toll. For these reasons, “hotels” will not likely increase the populations of cavity-nesting bees.
People don’t realize what they are getting into. Proper management and sanitation is critical for the health of these bees and wasps. The Xerces Society has a fact sheet that explains the complex procedure needed to ensure their heath. Most people don’t have the time, the interest, or any understanding of bee life cycles. Most people will not care for them properly. These “bee hotels should not be recommended without warning of the dangers associated with them and giving proper management instruction.
Your website is excellent for information on bee species and I recommend it highly but please do include some information and guidelines on how to protect cavity-nesting bees and wasps so that people can make an educated choice for their use.
Sincerely, Holly Kocet,
Protect Our Pollinators (Propollinators.org)