I culture fruit flies for a few generations and these are the same cups that the fruit flies come in, so they are perfect! I have also used these to contain baby jumping spiders for the 1st 7 - 10 days of life, after they have had thier 2nd molt. I keep a damp (not wet) paper toweI folded twice in a square along the side of the container and spritz it with an ultra fine mist as needed. I also set a light weight (previousy baked) apple tree branch inside in an upside down position. I tip the container upside down on top of a wide mason jar ring to allow for air to circulate., The baby spiders will settle on the sides and top-most part so accessing the inside is easy. If there are any babies on the bottom, (top) when I need to open the lid, I gently tap on the lid and they will drop on thier silk and move away from the lid. I hatch the common flies in these cups as well. These are a must when I breed silk worms or hornworms. These are wonderful for dumping the feeding time crickets in and covering. I've used these cups for multiple purposes with my crew of critters. I would highly recommend these cups.

I've been using these for years for my fruit fly cultures