Protoptila erotica Ross, 1938
Basis for Listing
Protoptila erotica (a species of saddle casemaker caddisfly) is known in Minnesota from only three collections. The first occurred in 1937 near Rice Creek in Anoka County (Anoka Sand Plain); however, significant changes to the habitat have occurred since that time and the wetland is no longer present. Since 1937, P. erotica has been collected only twice despite extensive, statewide survey: 100 adults were observed or collected in the Otter Tail River in Becker County (Pine Moraines & Outwash Plains) in 1982; four adult specimens were collected from a large riffle of the Kettle River in Pine County (Mille Lacs Uplands) in 2001. The overall distribution of the species is enigmatic — it ranges from Arizona to Michigan but is rarely abundant. Protoptila erotica was listed as a special concern species in 2013.
The larva, specifically, of P. erotica is unknown. Mature larvae of the genus Protoptila (saddle casemaker caddisflies) range 3–4 mm (0.12-0.16 in.) in length. They have a cream-colored abdomen with a darker head and thorax. Larval cases resemble domed turtle shells and are composed of small rock fragments. Adults are 3–4 mm (0.12-0.16 in.) in length, light brown in color, with a lighter transverse stripe on the forewing. Macroscopically, they are indistinguishable from other species of Protoptila or even from species in the Hydroptilidae (purse casemaker caddisfly family). Adults can be definitively identified only by a close examination of the terminal abdominal segments under a microscope. Houghton (2012) has developed an identification identification manual and key to the caddisflies of Minnesota to the caddisflies of Minnesota.
Little is known about the specific habitat needs of P. erotica in Minnesota. Protoptilines are typically found in large warm rivers where they consume epiphytic algae from the surfaces of rocks in shallow water. The species has been found in small streams in Michigan. The most recent collecting site in Minnesota, the Kettle River, is a large, deep, fast-flowing, and fairly undisturbed river that carries the state designation of “Wild and Scenic”. The Becker County site is the Otter Tail River, a small stream connecting Hubbel Pond and Height of Land Lake. Hubbel Pond is a semi-permanent wetland of 243 ha (600 ac.) with 37 km (23 mi.) of shoreline.
Biology / Life History
Little is known about the specific life cycle of P. erotica. Larvae probably live for a year under the water feeding on epiphytic algae growing on rock surfaces before emerging as adults in the summer. Protoptila erotica has been collected in Minnesota in June (Anoka and Pine counties) and August (Becker County).
Conservation / Management
Little is known about the specific conservation needs of P. erotica. The Kettle River is fairly well-protected by Banning State Park, while the Otter Tail River is protected by Hubbel Pond WMA. Any future development of the riparian corridor of these rivers or any changes that would decrease water quality or increase water temperature should be approached cautiously to preserve these two isolated populations. The Anoka County population has not been rediscovered despite extensive survey efforts. Further research is necessary to identify any additional populations of the species as well as its specific habitat needs.
Conservation Efforts in Minnesota
Field surveys in conjunction with a University of Minnesota study on the Caddisflies of Minnesota (Houghton et al. 2001) have been conducted to search for additional populations of this species, and an identification manual and key to Minnesota caddisflies has been developed (Houghton 2012).