There was a fly on our window which – at least it looked like – had fleas. Could that or what else could it have been? Does the fly suffer from parasites?

Answer

Dear Pim,

You still have to have very good eyesight for your age to distinguish those tiny arthropods with the naked eye.

What you noticed were probably mites that got carried away with the fly (see photo of stable fly with a whole load of mites). By attaching themselves to a flying insect, the mites reach new feeding and breeding grounds. Some of these mites (Macrocheles) feed on the eggs and young larvae of the fly and will leave the fly once the fly has landed on its nesting site. That way they can be sure of their meal.

Regards

Redgi The Blanket