I found out what this beetle was. For future reference the wildflower is St John's Wort and the beetle is a biological control that was released to control it.
From
http://www.omafra.gov.on.ca/english/crops/facts/info_sjwbeetles.htm :
"St. John's wort, a
native of Europe, was first introduced to North America in 1793 in Pennsylvania. It became established in Eastern Canada by 1883. Over much of its range in Canada it has been successfully controlled by the introduction of insects that
feed only on St. John's wort. Biological control of St. John's wort was introduced in Australia in the 1930's with the introduction of three beetles that fed only on St. John's wort in its native habitat in Europe - Chrysolina hyperici from the Atlantic region of Europe; C. quadrigemina from the Mediterranean region and Anaitis plagiata from northern Europe. During the 1950's Ontario imported and released all three species in an effort to achieve similar biological control of St. John's wort. C. quadrigemina is currently predominant.
Chrysolina quadrigemina is a member of the Chrysomelidae, the same insect family that contains the Colorado potato beetle. Its shape and habits are similar to those of this common and destructive pest of solanaceaous plants. When disturbed, Chrysolina spp. beetles will drop from the plant and "play dead" on the soil. They feed voraciously both as larvae and adults."
The chrysolina beetle only ate the St John's Wort and didn't make much of a dent in the plants. The beetles were done and gone by the end of July.
I thought it was all very interesting!