Your insects look like black fireflies.
Adult blister beetles are long, narrow beetles
(0.5 to 1.25 inches long) with a broad head and antennae that are straight and about one third their total body length. 
One type is 1/2 - 3/4 inch long with a Ant-like head. Head, prothorax (behind the head) and wing covers are dull green with orange and black legs.
 There are other several species, including black, ash gray or striped beetles.  Each species have unique color patterns.

https://apps.extension.umn.edu/garden/diagnose/insect/garden/beetles/large/blisterbeetle.html

https://insectlab.russell.wisc.edu/2020/01/30/blister-beetles-wisconsin/

Thank you!

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