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?
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?
In this section, the Midwestern nymphs (#573 & #574) with the dark irregular ventral bars across the anterior portion of the sternites look like Maccaffertium mediopunctatum arwini
(the Midwestern ssp.), but the two Eastern duns (#733 & #765) and the associated shuck (of #765) and nymph (#764) look more like Maccaffertium ithaca
species can have very similar ventral markings in the nymph—dark, sinuate, chevron-shaped bars on many of the sternites and dark lateral marks (sometimes connected to form an inverted U-shaped mark) on segment 9. The Eastern mediopunctatum
subspecies, M. m. mediopunctatum
, has these markings, as does M. ithaca
. Similar markings also appear as a less-common variant marking of M. modestum
(or the M. modestum
species complex). However, these species differ in the length and location of posterolateral projections, leg markings, the appearance of the subs and adults, and size.
Although interpretation of posterolateral projections can be tricky, those projections should help to separate the nymph (and husk) from mediopunctatum
. On mediopunctatum
, projections are usually on segments 3-9, 4-9, or 5-9, and those on 8 and 9 are fairly long. On ithaca
, projections are usually on segments 6-9 or 7-9, and those on 8 and 9 are somewhat shorter (when compared to mediopunctatum
). The twin brown bands on the femora of the nymphs should also help to separate them from modestum
(usually three or four in those species).
The brown posterior margins and median dorsal stripes of the duns (similar to those found in M. vicarium
) are typical of ithaca
. In McDunnough’s original description of mediopunctatum
(1926), he mentions that some of his (paratype) specimens were reared from subimagos, and he describes those subimagos as “quite pale whitish in coloration.”
Size might also be somewhat helpful in distinguishing these specimens from M. m. mediopunctatum
(about 7-10 mm at maturity) and modestum
(about 8-11 mm at maturity). M. ithaca
is about 9-14 mm at maturity. The relatively mature nymph (#764) is at least 11 mm, the female dun (#733) is about 13 mm, and the male dun (#765) is about 11 mm.
When all of these factors are considered, it seems to me that M. ithaca
is a more likely ID for the Eastern specimens. (See Bednarik and McCafferty 1979 and Lewis 1974.) I would suggest the following placement for specimens currently in this section:
female dun: http://www.troutnut.com/specimen/733
male dun: http://www.troutnut.com/specimen/765
M. mediopunctatum arwini
M. mediopunctatum arwini