Wow that is unusual. Do you do anything to get rid of them? How long do they stay there? Is it sunny/get any sun at that location?
Considering the various sizes of the sac-like shapes, I'm going to guess this is some kind of fungus. Maybe slime mold.
I think your answer will confirm or reject my guess.
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Within the category of “What is it?” lives a strange-looking organism called Nostoc. During summer 2014, several people brought in samples of a green jelly-like substance growing in their lawns. After a bit of digging, I identified the stuff as Nostoc sp., a genus of cyanobacterium formerly classified as blue-green algae. Nostoc has many colorful names including witches’ butter, mare’s eggs and meadow ears, among others.
It looks like specifically Nostoc pruniforme -- the ones also called "Mare's eggs"
...which led me to this -- I knew I had seen that term before
The Mare's Egg by Carole Spray The Mare's Egg
by Carole Spray
Permalink: https://www.amazon.ca/dp/0920656072
Learning never ends because we can share what we've learned. And in sharing our collective experiences, we gain deeper understanding of what we learned.