Phoresy - mites on ground beetle - how do you know if they are parasitic?

Notice the mite on the ground beetle.  Is it phoresitic or parasitic?

My previous blog was on a group of arachnids called oribatid or beetle mites, which are commensalistic organisms that hitch a ride on certain beetles.  They benefit; the beetle is not harmed.  Doing that blog reminded me of some other photos I had taken of a ground beetle (above photo) and a carrion beetle (below) that had mites on them.  I had previously thought they were parasites, but I learned of this behaviour called phoresy in some creatures.  Phoresy is a relationship between two organisms where one travels on the body of another organism without parasitizing it.  

Carrion beetle with mites attached (arrows).

This brought me to the question, how do you know if a mite is in a parasitic or phoresic relationship with the beetle it is on?

Mites, like the oribatid ones in my previous blog, are attached and do not seem to move.  However, they have certain characteristics such as hard, armoured exoskeletons, dark brown colour, and their biting mouthparts are not attached to the beetle, but rather tucked underneath them.  The mites above are clearly not the same type.

Although the photo was taken 12 years ago, I remember the moment well.  The creatures were crawling on top of the beetle freely and were not attached to it.  I took some time to remove each one (there were three) as, at the time, I thought they were parasites (see image below).  Now I believe they were phoretic mites hitching a ride.  I suppose that it is possible that they would eventually parasitize the commensal host, but I don't think so.

Carrion beetle with the mites removed.  Does it look happier?

The ultimate understanding would involve identifying the mite species and what its characteristics are.  This is above what I can do.  

Anyway, it was a cool discovery at any extent.  And I am glad I took the time to research it a bit more.

Thanks for reading.

Eric Svendsen     www.ericspix.com