Blood on Eggs

[Morning_Song]

Why would mites/red mites cause a bloody smear on an egg? This is new to me. I looked up this topic, of course, because my daughter collected a smeared egg. We do have 3 pullets but if they have started to lay, they didn't lay a little one first that we found they laid an average egg from the start. I know I should take a closer look at the combs but spring is crazy busy already

Thanks all