Mason Bees - Ask Extension
Hello,
I have a mason bee house. I checked one day to see if the cocoons I got had hatched and discovered a bunch of larvae in one spot and then one ...
Knowledgebase
Mason Bees #786967
Asked April 15, 2022, 7:36 PM EDT
Hello,
I have a mason bee house. I checked one day to see if the cocoons I got had hatched and discovered a bunch of larvae in one spot and then one making what looks like a normal way of a mason bee to make a nest. So I'm trying to figure out why there's a group of larvae and if they are mason bees or could they be something else? My friend suggested I email you guys. We are in Vancouver, WA.
Clark County Washington
Expert Response
Hi Brandy,
It looks like you have a fly pest of mason bees known as the Houdini fly (Cacoxenus indagator):
https://agr.wa.gov/departments/insects-pests-and-weeds/insects/apiary-pollinators/pollinator-health/houdini-fly
The build up of this pest can be reduced by cleaning out your blocks every fall, rather, than what I think you may have done, allowing your cocoons to sit in your blocks all winter. By cleaning the blocks you break the cycle of this pest. Look for a Master Gardener block cleaning session to learn how to do this and you should have minimal reinfestation from this fly in future years.
It looks like you have a fly pest of mason bees known as the Houdini fly (Cacoxenus indagator):
https://agr.wa.gov/departments/insects-pests-and-weeds/insects/apiary-pollinators/pollinator-health/houdini-fly
The build up of this pest can be reduced by cleaning out your blocks every fall, rather, than what I think you may have done, allowing your cocoons to sit in your blocks all winter. By cleaning the blocks you break the cycle of this pest. Look for a Master Gardener block cleaning session to learn how to do this and you should have minimal reinfestation from this fly in future years.
