Clinger nymphs are shaped that way to hang in really fast currents. Really? 13 Replies »
It is commonly held that clingers are flattened to make their lives better adapted to faster water. Their teardrop shape is certainly a classic symbol of aero and hydrodynamic perfection, so there must be some connection, right? It seems to me that such ideas show a complete misunderstanding of the hydraulic reality in which they live. Current is negligable even in the fastest a few mm. from the surface of solid objects. In fact, it is actually quite calm. I've observed baetids clinging by their tippy toes to the tops of rocks in fast riffles with no apparent effort, often next to clinger species that look like they're hanging on for dear life. What if clinger nymphs are flattened not to hold their place in fast currents but rather to facilitate movement in their ecological niche of the cramped spaces under and between cobble or crevices in other substrate types?ReplyClusters of midges and the Griffith's Gnat 35 Replies »
It is also thought that the gills of some species form ''suction'' to hold them in place. Since suction is a phenomena of vacuum creation in the atmosphere, how are these nymphs accomplishing this underwater? Is it their ultra delicate gills that hold them in place or a firm claw grip? The horizontal sprawl of the legs masks this as the gills stay in place until the legs brake free. Exposed to the air, the gills seem to laminate against the rock, just as crepe paper would if first held underwater before a rock was lifted out into the air from underneath it. However, underwater their gills behave like the crepe, flowing freely. They are performing their function as gills not suction cups. I find it hard to believe they evolved the way some think merely so they can make it more difficult for humans to pluck them from rocks in the atmosphere. How is it these mighty structures that defy our attempts to pry them from the rocks curiously fall off so easily when prodded for inspection a few seconds later in a tray or jostled in a container on the way home?
Even many scientific papers have encouraged these dubious beliefs so it's not just angler myth... And they go unchallenged... Thoughts?
Last reply on May 22, 2015 by Taxon
Replygrannom caddis 51 Replies »
This is a spin-off from a tangent in another topic
which seems worthy of its own thread.
I wrote about the midge I photographed:
I'm not sure how a griffith's gnat is supposed to imitate such a thing
Schwiebert's theory was that when it was awash in the film, the herl and halo of hackle suggested the loosening pupal shuck around the dark body of the emerging midge. Others have speculated that it imitates a cluster of midges. Both theories are reasonable, I suppose, depending on the size of the Griffith's Gnat that is effective relative to the size of the actual midge. Like many anglers, I just know that it does work. :)
Those are the explanations I've heard, too, but I'm skeptical of both. I'm not doubting the effectiveness of the Griffith's Gnat; I just think people have traditionally stretched the bounds of credibility when trying to explain a fly's success in imitative terms, and this is one of the more prominent examples.
Has anybody here seen a cluster of midges on the water? I haven't. I have seen midges thickly grouped on rocks next to the water, and I don't doubt that they occasionally fall off of there, and probably sometimes two are three are clinging to each other. I've also seen early-season stoneflies balled up with each other in an opaque little (presumably mating-related) clump on a midstream boulder, and I wouldn't be surprised if some midge species do something like that too. But trout don't see balls of midges floating around very often on any stream I've ever observed. Has anyone experienced that?
In either case, I can't see something so opaque as a Griffith's Gnat effectively imitating what would surely be a loose ball of gangly entangled midges. You would have to roll them around in your fingers for a while to goo them together so solidly.
I just can't see the herl and hackle imitating, or even suggesting, a loosening pupal shuck. Shucks don't get that
loose. They trail behind length-wise; they don't balloon to the sides. And they aren't pointy. Of course I'm sure Schwiebert knows all that and was just trying to add an idea to the mix of explanations, but I do find that one as far-fetched as the others.
Here's another far-fetched guess: maybe the hackle and refractive trickery in the surface film reduce the perceived thickness of the fly and it passes for a single midge pretty well. This could be tested in an aquarium but it's late and I'm feeling lazy.
I think it's more likely that when trout take a Griffith's Gnat they're only looking for (at most) the right general size and color. It's not as fun, but sometimes
things are really that simple.
Hi All! I was reading through the site and I happened upon the Grannom (Apple) Caddis page, which made me wonder. Here in PA it is called The Mother's Day Caddis, I believe. Adults, which trout rarely feed on, are imitated with black or peacock herl bodies. The pupa, or emrgers I guess, we imitate with a wet fly. It has a peacock herl body and brown hackle for the legs, etc. in a size 14. Is this the same Grannon as the apple Grannom? Just curious!Replyovipositing? 6 Replies »
I still get confused by these caddis and I'm trying to narrow down a list of caddis patterns and colors to cover the largest percentage of the hatches throughout the year.
I had a large swarm of black sedges in a size 16 ovipositing today.the females hadvblack wings and body with a green egg sack was just wondering if that is this genus or something totally differentReplyrotunda 8 Replies »
Your post on Ephemerella subvaria brought back some memories that might be of interest to some readers. Reply
I got my master’s degree under Ed Cooper at Penn State in 1966. I studied the impact of low oxygen from Penn State’s sewage plant on the mayflies of Spring Creek. The plant mostly removed BOD (organic matter which causes low oxygen) by oxidizing it in a bacteria rich environment. But at that time the plant did not remove phosphorus (and nitrogen) which fertilized the macrophytic algae and other plant growth. There were far more macrophytes (large plants) in Spring Creek below the sewage plant entrance than above, and essentially no mayflies. What was there in the effluent that killed the mayflies? Mayflies put directly in the effluent did not die over a 16 hour day. But oxygen samples taken over 24 hours in summer showed a much greater variation below the effluent (from 16 ppm (or mg/l), 160% of saturation in late afternoon) to 3 ppm (30 percent saturation just before dawn) (vs 14 to 10 ppm, +- 20 percent saturation above the effluent.
I built a Rube Goldberg machine in the lab that would control the oxygen levels and temperature of control and experimental cages that each held 25 mayflies. The control would keep oxygen near saturation and the experimental one would lower the oxygen over 8 hours (the length of night in summer). Mortality was dependent upon both oxygen level and temperature. Virtually no mayflies would die if the oxygen was above 2 PPM (or mg/l) at 8 C, or at 4.5 at 20 C. Seventy five percent of larvae would die at 1 ppm at 8 degrees and 2.5 ppm at 20 degrees. So the mortality was much more if the temperatures were high. Hence most of the mortality would presumably occur in August when the high temperatures (20C) would increase the larvae metabolism and hence need for oxygen, but the water would hold less oxygen even before the night-time respiration of the macrophytes would reduce it much further (to only 3 ppm). Thus the low nighttime oxygen caused by excessive plant growth was a sufficient cause or the near total absence of mayflies below the sewage plant. Recognizing the aquatic impact Penn State started to use land disposal of its effluent which as far as I knew alleviated, and even stopped, the negative impacts on the mayflies. Can anyone verify this ? The otherwise well done “The Fishery of Spring Creek; A Watershed Under Siege “
By Robert F. Carline, Rebecca L. Dunlap Jason E. Detar, Bruce A. Hollender Has nothing on dissolved oxygen or aquatic insects. In my opinion we need much more of an ecosystems approach for streams (Which we are doing for Little Sandy Creek in N.Y.).
Now back to Ephemeralla subvaria. The title of the paper I published on this project (my first of nearly 300 publications) was:
1. Hall, C.A.S. 1969. Mortality of the mayfly nymph, Ephemerella rotunda, at low dissolved oxygen concentrations. J. Elisha Mitchell Sci. Soc. 85(1): 34-39 (M.S. Thesis, Pennsylvania State University, 1966).
Whoa! Ephemeralla rotunda? This was by far the most abundant mayfly in Spring Creek where I sampled! But I could not even find the name in your list. Also I had my samples verified by Burke, author of the authoritative "Mayflies of Illinois", and he said Well that’s what it keyed out to in my book”. (Talk about scientific ass covering! ) Well to make matters worse (as of 24 hours ago) my next girlfriend, Molly, at the University of North Carolina, loved the name of “Ephemerella rotunda”, the rotund one, which comes to think of it described her as well. I liked it too. But n’exist plus: where had the most abundant mayfly gone? Fortunately upon reading the rest of the post I found “Ephemerella invaria is one of the two species frequently known as Sulphurs (the other is Ephemerella dorothea). There used to be a third, Ephemerella rotunda, but entomologists recently discovered that invaria and rotunda are a single species with an incredible range of individual variation." Ahh neither rotunda nor Molly stood the test of time. So I assume what I called rotunda is still alive and well in Spring Creek as invaria. Again, can anyone verify that?
If anyone wants to follow up on the distribution and abundance of mayfly (or any other species) may I recommend: Hall, C.A.S., J.A. Stanford and R. Hauer. 1992. The distribution and abundance of organisms as a consequence of energy balances along multiple environmental gradients. Oikos 65: 377-390. I can send it if you cannot get it from google, which I think you can. (email@example.com)