#aquaticinsects

This infographic is dedicated to a very unique genus of caddisflies!

Rhyacophila is the sole genus in the family Rhyacophilidae. Unlike other caddisflies, Rhyacophila is considered to be a "free living" genera. Most caddisflies are net or case makers. Similar to snails, case making caddisflies construct portable hides out of various natural materials. The size, material and shape of these cases is vital in regards to taxonomic identification. Net spinning genera construct nets out of silk and are fixed to rocks, so the insect is free to leave and return as needed. The nets also allow for the passive collection of food.

Rhyacophila does not utilize either strategy as a larva, and only builds a "case" when it is in pupation. Since it cannot passively acquire food, the insect must go out and scavenge. Rhyacophila can be predacious or herbivorous . The consumption of plants gives the genus its nickname "green caddisflies" as they can accumulate chlorophyll in their bodies, which makes them a distinct bright green.

Rhyacophila is a very vulnerable genera to both predation and environmental factors alike. Caddisflies as a whole are environmental indicators, and are extremely sensitive to water pollution. Their presence or absence can clue in to the overall health of a water body. There is an index utilized by scientists called the NCBI or "North Carolina Biotic Index". This index includes state specific taxa, and rates each by their tolerance to pollution on a 0-10 scale. 0 being the least tolerant and most vulnerable, and 10 being the most tolerant. Rhyacophila is one of the few taxa to score a 0 on this list, so its presence indicates very pure and oxygen rich water!

In my time working as a macroinvertebrate technician, I have seen this genus in a handful of samples, so they are very special! When preserved in ethanol, they lose their green tint and turn a very pretty purple color, their abdominal sections are noticeably segmented. Another curious detail is the twisting "foretrochantins" which are shoulder-pad like projections on the first leg segment pairs right beneath the head.

https://www.tn.gov/content/dam/tn/environment/water/policy-and-guidance/DWR-PAS-P-01-Quality_System_SOP_for_Macroinvertebrate_Stream_Surveys-122821.pdf

My first time drawing a Dipteran genus. This is the larval stage of Blephericera or "Net Wing Midges", contained in the family Blephericeridae.

Blephericera larva are very distinct from other Dipterans in my opinion. One of the most distinct characteristics is the highly divided abdominal segments, and large, helmet shaped cephalothorax. Another identifying feature, and adaptation is their abdominal suckers. Note the Ventral drawing on infographic, on their underside, Blephericera has suckers or "creeping welts" that allow the insect to better attatch themselves to smooth surfaces.

It is to note on the NCBI Taxa List for TN, Blephericera has a score of 0/10, which is very special! This prestigious score indicates very specific enviornmental needs. These needs being, fast moving, cool, well oxygenated and pollutant free water. The fused cephalothorax reduces drag from water currents, and the suckers keep the insect in place.

The larvae themselves are primarily herbivorous, mostly being scrapers, grazing and sometimes filter feeders. Adult females, however have been recorded to be carnivorous. Curiously, the pupae have been known to be preyed upon by Rhyacophila larvae (yet another genus with a 0/10 NCBI score). Since Blephericera is a specialist, it has few predators (Rhyacophila aside).

Another member of the Hemipterans or “true bugs"is Nepa! Nepa is a member of the family Nepidae, which includes the “Water Scorpions” and are best known for their two representatives Nepa and Ranatra. Water scorpions are related to Lethocerus (and Belostomatidae in general) and are quite similar in appearance and habitat.

Nepids have earned the title of “water scorpion” because of their notable abdominal snorkel which loosely resembles the tail of a scorpion. Unlike their arachnid “counterparts”, this “tail” is completely harmless to humans and is used to intake atmospheric oxygen while the insect is submerged under water. Another feature that relates them to scorpions is their large raptorial claws, which (again) loosely resemble pincers. 

Though the claws and pincers differ somewhat in appearance, in functionality they are quite similar. Nepidae are ambush sit-and-wait predators, and despite being aquatic, are clumsy swimmers. So, to circumvent this, they cling to anchors in the water (this can be anything solid; plants, litter, branches etc) and simply wait until something smaller than them swims close enough. Upon this, they snatch their prey with their claws, and use their piercing mouthparts to subdue, and consume their meal. 

Nepa is of moderate pollution tolerance, ranking a 6.3/10 on the NCBI list. Since they do not absorb oxygen from the water, they are less influenced by pollutants. 

Nepa can be found in slower or still bodies of water like lakes or ponds, typically in shallower sections of the water body. Again, they are poor swimmers, and rely on clinging and climbing to navigate, so they need to be in areas shallow enough to have vegetation to hide and hunt in. Nepids in general are masters of disguise, their coloration is typically drab, and resembles decaying organic matter. Body shapes range from slim and mantis-like (Ranatra for example looks like pine needles) to larger and more broad (Nepa is generally leaf shaped). These camouflage techniques help them go unnoticed by prey and other predators (their uncanny ability to be motionless is also helpful). 

Functionally in ecosystems, they can be water quality indicators, and as predators serve as vital mechanisms for population control. I have read from individuals who keep Nepids as pets that they have a favor for Culicid larvae (Culicidae are mosquitoes!). So we can all cheer to know that their favorite snack is one of our greatest foes.

https://www.tn.gov/content/dam/tn/environment/water/policy-and-guidance/DWR-PAS-P-01-Quality_System_SOP_for_Macroinvertebrate_Stream_Surveys-122821.pdf , see page 220 for Hemipteran NCBI scores

Ranatra, courtesy of INaturalist

Probably the most badass aquatic insect of all time, the Hellgrammite!

Corydalus is a genus within the family Corydalidae, and are often referred to by their nickname “Hellgrammites”. 

Beloved by fishermen, these sturdy larvae are known for their centipede-like appearance and large mandibles. Hellgrammites are voracious predators, and actively seek out prey like other smaller invertebrates. They can be found in a variety of aquatic systems, such as;streams, spring seeps, lakes, ponds etc. They are generally found where detritus is abundant. Another distinct quality hellgrammites have are their long, feather-like filaments that adorn their abdomen. The head and thoracic segments are sclerotized  and are often highly patterned. 

As far as water quality indicators go, they have an average tolerance for pollution, scoring a respectable 5.2/10 on the NCBI. To respire, they have tracheal gills (which would be found where the “neck” would be on the insect). 

The development from larvae to adult ranges from 2-5 years, and their pupation stage is terrestrial. Once emerged as adults, they are dubbed as Dobsonflies.  Akin to mayflies, adults do not eat, and emerge solely to reproduce and then die. In regards to reproduction, Dobsonflies display sexual dimorphism and sexual selection. Male specimens have long tusk-like mandibles as adults, which are used in mating rituals in competition with other males. In research it has been noted that longer/ larger mandibles in males are preferred for mating females.