Ptinus sexpunctatus 6 spotted spider beetle not a welcome visitor to Red Mason bee nests!
I found several of these beetles when cleaning out an orchard solitary bee nest box, containing Red mason and leafcutter bees. I do not know how they arrive whether they fly in as adults or crawl inside and lay their eggs. They and their larvae feed upon the detritus inside the nests. However, it has been listed as a natural enemy of Osmia bicornis and O. caerulescens, thus I suspect that the larva would compete with the bee larva for the stored pollen provisions. It may well then eat the dead larva after out competiting with it for the provisions, hence the listing. It has been found in the USA.
Without spending hours on the internet I cannot find out how adults find their way into the nests in the first place to lay their egg(s) nor how they go about doing this when a female is provisioning a nest, or whether they lay an egg on the completed mud wall and the larva chews its way inside to consume the pollen. If any one knows please let me know. Thanks.
Adult photo courtesy of Paul Quigley and larva from Bee.safe.eu with thanks.
Filmed using my solitary bee observation nest nest box
See also Solitary Bees by Ted Benton available from Pelagic Publishing
For more information about solitary bees see BWARS
For info and link to buy an excellent book Field Guide to the Bees of Great Britain and Ireland by Steven Falk
An extremely useful resource supports this book by a special web site feature within Steve Falk’s Flickr web site which furnishes extra photos and other useful resources to assist with identification.
Intersted in Citizen Science and pollinators? (e.g. bees!) The Buzz Club