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Flotsam harvesting

Flotsam harvesting
Nashua, Hillsborough County, New Hampshire, USA
April 20, 2007
When areas are flooded by heavy rains or other means, considerable flotsam results in the form of stems, twigs, trash , and other debris, and clinging to it for dear life are thousands upon thousands of terrestrial arthropods.

Recently, after heavy non-stop rains, I noticed a runoff catchment basin was brim full and decided to investigate the concentration of flotsam the stiff wind had pushed to one end of the expanded body of water. I was already dressed for the rain with rubber boots and rainsuit and I had my sweep net with me. I scooped up a net full of flotsam and dumped it out on a flat surface, pawing through it looking for beetles. The material was loaded with all sorts of very active spiders but I also began finding wet, bedraggled beetles.

I stayed for a couple hours, discovering that the favorite type of flotsam was plastic foam objects from packing material to coffee cups. Often these pieces of trash were refuge to scores of beetles, mostly tiny roves and phalacrids. I also saw springtails, bugs, flies, mites, centipedes, millipedes, and spiders-a-plenty as well as one camel cricket or something similar that I lost. At home I later found three tiny pseudoscorpions.

The next day after work I went home, got a medium-sized plastic trash barrel, two five-gallon buckets, and a telescoping extension pole for my sweep net. Returning to the now somewhat-receded catchment basin I began fishing out floating pieces of plastic foam, getting plenty of organic debris in the process.

I am less than halfway through sorting my haul of flotsam and have collected more specimens than I can possibly do a decent job of photographing. I have discovered that under the conditions I experienced flotsam can be an arthropod gold mine.

This image was captured two days after the rain stopped and water has receded substantially. I didn't attempt to collect any more arthropods on this visit.

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"I am less than halfway throu
"I am less than halfway through sorting my haul of flotsam and have collected more specimens than I can possibly do a decent job of photographing"

Don't let that stop you! :D
I remember that flood! I was a volunteer member with the Nashua River Watershed Association before leaving for college. Come to think of it, We might have had to cancel our water sample that week because of the floor. When the water receded, there was a slippery layer of mud that was left on the parking lot of BAE Systems there by the river.

Your finds are amazing and quite surprising (I'd normally expect the poor things to have drowned or been swept away by the currents).

If the catch basin had overflowed into the river,
I'm sure most of these guys would have left town on a raft :-)

I have noticed that many beetles seem to have a "dive reflex" that slows their metabolism way down when they get wet. Some species are very sensitive in this way to water and will "die" if even their antennae get wet, reviving only after they're dry.

I first became aware of this reaction when I checked a dung beetle trap after a heavy rain, finding several of the poor little guys that had drowned in the few inches of water that had accumulated. Well, they started reviving as I was photographing their corpses. Last year I had a couple ironclad beetles escape and land smack in my toilet where they sank immediately (*iron* clad, you know). They could have been there quite a few hours. I thought they might be doing the low metabolism thing. Sure enough, when they were dry they began moving.

Investigating this phenomenon would make the basis of a doctoral thesis I should think, supposing it hasn't been done already.

Really intriguing info!
I don't know if you've seen any of my posts, but I rescue A LOT of insects from my landlord's pool. The vast majority of beetles that I have pulled out of the water in an apparently dead state, did indeed later revive (sometimes hours later). The most vivid memory I can recall of this phenomenon was a Coelocnemis that was floating legs-up and was completely unresponsive as I jostled it around trying to get some pics. I was concentrating on trying to get a good detail shot of the paired rows of golden setae on he tibia and when I noticed one small claw start twitching... I have also had several experiences with Cremastocheilus species which took multiple hours to reanimate. (I might add that many hymenoptera species also seem capable of reviving from an extremely lifeless and bedraggled state.)

pools are magnets for flying insects. OTOH, I'm pretty sure my flotsam harvest did not result from flying insects landing on the water since it was cool and very inclement. I think the rising waters just floated them out of wherever they were hiding.

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