Parasitic Mites on Corixids

I ventured out recently, broke the centimetre-thick ice on a local pool and underneath, found abundant Corixids happily over wintering and unbothered by the cold. Among the species I found was this specimen of Callicorixa praeusta: 

You may notice the small red object protruding from the rear end. Looking closely, this was a mite attached to the bug rather than part of the Corixid: 

Phoretic (hitchhiker) mites are not uncommon on Arachnids but a little research told me that this was in fact the larva of a Hydrachna water mite.

These larvae are actually parasitic rather than phoretic, feeding on the haemolymph of the Corixid. There is some interesting information here: http://coo.fieldofscience.com/2014/12/hunter-balls-hydracha-water-mites.html  They are not as common on Corixids as on some other Arachnids and I have no idea how much harm they inflict on the host. 

Great fleas have little fleas upon their backs to bite 'em,

And little fleas have lesser fleas, and so ad infinitum.

Augustus De Morgan