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Beetle beach party - Hippodamia convergens

Beetle beach party - Hippodamia convergens
Oval Beach, Saugatuck, Allegan County, Michigan, USA
September 22, 2014
I know what they are (mostly) but can anyone identify the reason why this Lake Michigan beach is currently hosting several thousand beetles? They are about 30 feet up from the water's edge, on driftwood and broken grasses left behind by stormy rough weather this weekend. I gathered a few clusters to make an informal count, and came up with about 90% Harmonia axyridis, with significant (6%) quantities of Diabrotica undecimpunctata, and several other lady beetle species too, including Hippodamia convergens, Hippodamia parenthesis, Coccinella septempunctata and Cycloneda munda. What brings this range of genera and species together in such quantity in this location? Preparing to hibernate? Migrate?

So interesting
I wouldn't mind seeing a few more pictures documenting this interesting phenomenon, a couple of other species, maybe?

I do have more photos
and probably with other species included. Will look them out and post a few more if they add anything.

Moved from ID Request.

lake-side beetles
Awesome photo!

John Acorn discussed this phenomenon in his Alberta ladybug book. (1) Apparently, it's often associated spring and fall migrations...


Lee, R.E., Jr. 1980. Aggregation of lady beetles on the shores of lakes (Coleoptera: Coccinellidae). American Midland Naturalist, 104(2): 295-304.

Iknow there's several other papers on this topic as well...

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