The Saddle Case Caddisfly.
The “holy grail” for volunteers participating in the Illinois RiverWatch program. The most sensitive of the sensitive. The best of the best. This is how the mysterious Saddle Case Caddisfly (Family Glossosomatidae) if often thought of by RiverWatch Citizen Scientists. And rightfully so, this aquatic macorinvertebrate is rated a “0” on the pollution tolerance index, meaning that finding it in your stream is great news! But, since this is such an important bioindicator, how can we be sure of the identification? This article aims to correct some misidentification problems that have been occuring through the years here at RiverWatch.
What Does A True Saddle Case Caddisfly In Its Case Look Like?
A true Saddle Case Caddisfly has tortoise shell-shaped case made out of gravel. The ventral side of the case is flat, and dorsal side is rounded. There is an opening at each end of the case for its head and posterior prolegs (fleshy appendages with hooks for anchoring) to protrude.
What Does The Saddle Case Larvae Look Like Outside The Case?
The Saddle Case larvae looks like most other caddisfly larvae, with 3 pairs of jointed legs, at least one thoracic plate, and posterior prolegs. For the saddle case larvae, look for 1 thoracic plate and 1 anal plate over the last abdominal segment.
What Could Be Confused With The Saddle Case Caddislfy? A Warning About Caddisfly Pupae.
Often times RiverWatchers find tortoise-shaped caddisflies stuck to the rocks in their stream. The case is often sealed at both ends, preventing the volunteer from seeing the animal inside. A sealed case is a “pupae”, which is what the caddisfly makes to metamorphose into an adult (much like the cocoon of a moth). Caddisfly pupae should not be counted for RiverWatch stream quality indication, so no further identification is needed once the determination of “caddisfly pupae” has been made.
But just for fun, how would you be able to know if a pupae was a Saddle Case Caddisfly? First of all, Saddle Case pupae look very similar to Hydropyschid Caddisfly pupae. To make the identification, you must look at the pupae body inside of the case. A Hydropsychid pupae will have split appendages on the end of the abdomen, while a Saddle Case pupae will not.
What Should Be Done With Caddisfly Pupae Then?
So, the moral of the story is to be cautious when identifying a Saddle Case Caddisfly! If it is determined that the caddisfly case is completely sealed at both ends, then it is a pupae and will not be counted for RiverWatch stream quality calculations. For best results, contact the RiverWatch coordinator if you think you have Saddle Case Caddisfly in your sample so that the coordinator can ensure proper identification.
So hopefully we can now say “case closed” with the case of the mysterious Saddle Case Caddisfly!