This beetle was crawling on the sidewalk near my lawn. It is interesting as much insect activity has ceased in this area because nighttime temperatures are dropping into the low 20's (about -5°C). When I brushed it away from the grassy fringe to get a better photo, it landed onto its back and I saw how heavily colonized it was.

I will post another picture of the underside, but even in this picture you can see how heavily colonized the beetle is--the brown froth between the middle and back leg is a clump of passengers.

Are these mites parasitizing a host, or are they baby beetles riding around on momma? I rolled the beetle over two more times to photograph the colony, and in all of this failed to dislodge even a single passenger. This makes me suspect that these aren't children, but rather firmly attached parasites. Any ideas?