If you have mason bees, fall is the time to collect and safely store the cocoons to increase their chances of surviving the winter. Mason bees forage actively from early spring to late May or June. The adults die as the larvae are metamorphosing into pupae. The pupae become adults in the fall, but overwinter inside their cocoons until they emerge the following spring.
The mason bee got its name because it uses mud in its nesting holes to separate the egg chambers. After each chamber is filled with food (pollen and nectar) and an egg, it is sealed shut with mud and the next chamber is then filled and sealed in the same way, until five to eight eggs have been encased.
Some bees take advantage of holes in fence posts or trees, but you can increase their survival rates by giving them nesting blocks to use so you can remove the cocoons from the nesting holes. Cleaning and storing the cocoons properly protects them from parasites and keeps them dormant through the winter.
Some people just drill holes in blocks of wood for mason bees, but drilled blocks can be difficult to clean and thus allow dangerous mold, fungi, or parasites to survive to kill future residents. Instead, you can place cardboard tubes with disposable paper liners (available in store or online) in the holes or use laminated block systems that when banded together form tube-shaped slots; these have the advantage of coming apart easily for cleaning.
Cocoon care
Cocoons are subject to infestation by pollen mites, wasps, dermestid beetles, and fungal pathogens that will eat not only the collected pollen and nectar, but also the developing bees inside. When you open the tubes to harvest the cocoons, you may see signs of predation or infestation.
There may be holes in the cocoons where wasps have invaded, bright yellow mite excrement (larval excrement is brown), or fungal infestations like chalk brood disease. Some larvae simply don’t develop, and their cocoons will be indented and not nicely rounded.
Be very careful when removing the cocoons from their tubing. Don’t use a sharp tool, but rather a screw driver or rounded nail file to disengage the cocoons.
Sort out the healthy cocoons from the indented or perforated ones, which must be discarded. The larger cocoons are female and the smaller are male. You will of course need both next spring.
Use a magnifying glass to check the remaining cocoons for mites. If you see them, you’ll need to clean the cocoons. This can be done by stirring them in a bleach solution of 1 tablespoon of bleach to 8 cups of cool water for a couple of minutes or by gently stirring them in a bowl containing dry sand. Use fresh sand for each batch of cocoons.
If you still see mites, repeat the bleach solution. For either technique, rinse in cool water and air dry on a paper towel or a screen for at least an hour.
You should then overwinter your cocoons in your refrigerator. The steady cold temperature of a refrigerator helps the bees use less energy as they lay dormant. They need a temperature of 39 degrees with 60 to 70 percent humidity.
You can assure the humidity by placing the cocoons in a ventilated container with a moist paper towel in a dish. Remoisten the paper towel every couple of weeks as needed. If mold develops, repeat the bleach bath.
If you didn’t do it this year, you can further increase your bees’ chances for survival by storing the nesting material in a protected location next summer to keep them safe from predators until you clean them in the fall. The Oregon State University Extension Service has an excellent publication available online entitled “Nurturing Mason Bees in Your Backyard in Western Oregon” that provides detailed information on all aspects of mason bee care.
If you would like to learn more, attend the mason bee workshop put on by the WSU Clark County Extension Master Gardener Program. Join Master Gardener Vione Graham for an introductory workshop on mason bees.
The presentation will cover their role in pollination, their life cycle and habitats, and how we can protect these valuable creatures. The event will conclude with a demonstration of nest/cocoon cleaning. If you have mason bee cocoons and a nest structure designed to come apart, bring them and plan to clean them. Also bring a medium size bowl (football size is good) and a container with a lid, such as a yogurt tub.
The workshop is Oct. 27, from 1 to 3 p.m. at the 78th Street Heritage Farm (head house); 1919 N.E. 78th St., Vancouver. The event is free and registration is not required. For more information, call 360-397-6060, ext. 5738 or Erika.d.johnson@wsu.edu. Visit us at extension.wsu.edu/clark/gardening/workshops-events.
Susan Cox is a Master Gardener volunteer with the WSU Extension.
