I saw several of these beetles marching through cut grass in the park. They seem to be a regular sight in the fall.
An American oil beetle marching grimly along.
They are known as American oil beetles or blister beetles because of an oil secreted from their legs when disturbed. This oil is a skin irritant and soon teaches victims to leave the beetles alone. This isn’t the only example of an ability to use chemicals to their advantage. In fact the life cycle of blister beetles stretches all credulity in addition to illustrating an amazing balance between parasite and host.
This BBC short tells the story of these amazing creatures (in this case in the Mojave Desert) better than I can.
Friends of Raymore Park 
I don’t think that the beetles have always been here. I saw my first one in 2008 in St. John’s Cemetery on the Humber (across the river from Raymore park). The eastern half of that cemetery is grassy and covered by ground-bee dwellings. Once introduced, the beetles’ population exploded. But because they are flightless, the expansion of their range is limited by the possible nonexistence of other nearby ground-bee habitats.
LikeLike
Thanks for the comment Hans. I have updated the video – the BBC took the original off YouTube but this one suffices.
In order to thrive, the beetles depend on good conditions for ground bees. I also wonder if there is an ebb and flow to the relationship. I must admit, I had no idea about them until I saw them in the park.
LikeLike