Ick. That is a lot of mites!

My best guess would be too much moisture in the bin. You're always going to have some mites in there, but I've never seen such a huge concentration. How wet is the bedding material?

Nice mite bloom! Believe it or not, this is not indicating that all has gone wrong with your bin and that there is now a major problem to be corrected. All is well with the world, but conditions in the bin are changing to select for high mite population levels that concentrate at or near the surface. Such behvior is almost always associated with a system suffering from low oxygen levels. Those mites arelikely simply seeking a nice breath of fresh air! Low air flow is most commonly caused by overly wet conditions where-in water displaces oxygen in the system, as Pet seems to be wisely thinking, but it can also result from the use of plastic bins with few air holes that are kept in locations that see little air movement around the outside of the bin.

Check the moisture level of the material in the bin and if it's very wet, consider mixing in some dry chunky material like old leaves, chopped straw or shredded cardboard or paper. Drill some 1/2" holes in the sides low near the bottom and high near the upper edge to allow air to better move through the system, and try keeping the bin in a location where air moves freely around it.

Know, too, that the number of mites you're seeing is not harmful to you, your worms or your pets. Most mite blooms dissipate over time as conditions in the bin no longer select for high mite popuations and/or when O2 levels are sufficiently elevated that the mites spread themselves throughout the system once again instead of concentrating on the surface where oxygen is plentiful.

Make sense?

Kelly S

Thank you Kelly. That makes perfect sense.
I tossed out the wall-clinging mites and the ones that had gathered on the melon rinds. I dug around and definitely needed to add dry bedding. I also increased the air flow as you suggested. Thanks for your help and wise advice.
Whew...what a relief to know that all is well in worm world :)
I got a few of my guys to pose for pictures this afternoon.

Here is a link that might be useful: worms are happy anyway

Ew, I'm having this same problem. I think it's b/c I fed them too much food and some of it was watermelon rind that I put through the food processor. Grody.