Found it on my son's hair after a 10min visit to our veggies garden. My guess is that it might be a tick but we are not in an area of lime disease and although it's an open, rather unkept, field the only mammals I see around are 2-3 stray(?) cats.

The photo was done using a stereoscope+smartphone. The dark lines underneath are .4 to .5 mm.

Any pointers would be welcome.