Invertebrates in the Fall - When does diversity really drop off?

In the regions of the world that experience frost and freeze, when does the invertebrate diversity really drop in terms of active inverts? Is it first frost? First freeze? Or maybe after a few sustained days with lows below 40F/4.4C or 32F/0C?

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When it’s lower than +10C in day and +5C at night there’s few to none active insects, lower it goes less insects stay active, but some spiders can be hunting even at pretty cold nights.


here in the eastern US my metric is usually the goldenrod. Some species of Solidago only start blooming at the absolute end of the summer and well into the early fall, once that food source for a lot of nectar feeding insects is gone thats when things really start to drop off (and when I find myself getting way more into soil and leaf litter guys lol)


Rubber rabbitbrush, Ericameria nauseosa, has the same niche in New Mexico. Once it’s done, most of the pollinators are too. Our first freeze is typically mid to late October, which kills the remaining annual sunflowers.

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Here near Minneapolis, Minnesota, we personally benchmark the demise of New England Aster as a drop off point. It probably takes a few below freezing nights to finish off blooms. Then it really drops off. For us that is usually by late October or very early November in wet years. This year has been very dry so that we are not certain how sustained will be the Aster bloom.

Yep, typically September is when things gradually start to drop off, in the beginning of Oct some flying insects are still around but it’s pretty much all over by the end of October. Varies quite a bit regionally, even in eastern Massachusetts the difference in growing season between inland, coastal mainland, and Cape Cod is 2-3 weeks.

edit: just reread your OP’s original post which was well-phrased (measured in terms of temperatures), but leaving my post in case there’s any interest.

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Yeah it lasts a little bit longer into October for me down in NJ, plus a lot of bugs seem to have some tolerance toward the first few weeks of cool autumn temps, but once that vital food source is gone most bugs are fully closing up shop

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Aside from college (where I wasn’t really naturalizing) I’ve never lived in a place that really has a frost. But there are some cool insects active in the winter, like snow flies.

There’s a project for winter-based observations too! Arthropods on snow


Very cool!

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Good to know. That makes total sense that good sources would play a huge role. I am also in the US where goldenrod is plentiful so I will keep my eye on it. Thanks.

That is neat! I will have to keep my eyes peeled for anything out on the snow. Thanks for sharing!

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