Thanks for the question.

We believe that what you are seeing is Physarum, otherwise known as a slime mold.  It is a very primitive organism.  It can quickly appear during hot and humid.  They are completely harmless and will not harm any plants.  They can simply be left where they are and should disappear shortly.  Here is some more information about them:

http://minnesotaseasons.com/Main/Slime_Molds.html

https://extension.umn.edu/lawn-care/common-fungi

http://minnesotaseasons.com/Slime_Molds/honeycomb_coral_slime_mold.html

https://ucmp.berkeley.edu/protista/slimemolds.html

Very interesting critters.  Enjoy.

Thanks for using this forum.