Hello Molly, happy to help.

Well, I had to educate myself about Lily leaf beetle (LLB) before writing to you. After all the conniptions I go through each spring, spraying my lilies with pest repellent to keep the rabbits and deer from chewing them down before they get a chance to bloom, now I've got to worry about LLBs. I may decide to find other tall plants to replace my lilies when the LLBs finally get over here in Hennepin county.

It turns out the beetle can live for several years, often overwintering nowhere near the host plant. They are strong flyers allowing them to roam far and wide, seeking out host plants. The larvae are the most destructive but there is only one generation per year. So when you saw more beetles later in the summer, it's likely you saw both older adults and newly pupated adults after the little pause.

Here is more information about LLBs from Wisconsin (since that state has been dealing with them longer than Minnesota). They've been noted by the MN DNR to have come into the state in 2020.

I love your description, "leaving them to drown in a sealed container of their dead cousins floating in some gross swamp water." Are you a writer? Have I seen you in The Loft classes? Keep it up. 

Good-luck!