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Trichoptera: Apataniidae of Gunnison County, Colorado

Allomyia gnathos

(Ross) 1950
Updated 20 Dec 2020
TSN 116445
The animals on the right were crawling around on the sediment and algae in a small headwaters stream of Copper Creek on 18 July 2007


Allomyia gnathos has a very unique head shape, the top of its head is dished, with a distinct lip.


They are common in small streams in the Gothic area. A few are found in the bigger rivers such as the East River and Copper Creek.


Ross 1950 did the last revision of the genus Allomyia as Imania.

Good Links

On this website:
Key to Apataniidae Larvae

Other Websites:
Photos, Map, Museum specimens, DNA - Barcodinglife.org


Alp,M; Peckarsky,BL; Bernasconi,SM; and Robinson,CT 2013 Shifts in isotopic signatures of animals with complex life-cycles can complicate conclusions on cross-boundary trophic links. Aquatic sciences, 75(4) 595-606. PDF

Àlvarez,M and Peckarsky,BL 2013 The influence of moss on grazers in high-altitude streams: food, refuge or both? Freshwater Biology, 58(9) 1982-1994. PDF
"1) Mosses in streams attach primarily to stable substrata subject to low hydrological perturbation, serving as shelter and as substratum for epiphytic algae, which are a food source for many grazing macro-invertebrates.
2) Given the changes in the hydrodynamic conditions occurring at substrata surfaces and the increasing habitat complexity, predator-prey interactions may be altered in streams dominated by moss, compared with those dominated by diatom-covered rocks. However, little is known about the relative effects of the food and refuge functions of moss and how they influence grazers in streams.
3) Results from a field survey indicated that streams with greater moss cover supported higher densities of less mobile, armoured, predator-resistant but disturbance-vulnerable caddisfly grazers than streams where moss was rare. However, the abundance of more mobile, disturbance-resistant but predator-vulnerable mayfly grazers was unrelated to the extent of moss cover.
4) To distinguish potential mechanisms explaining those observed relationships, we performed a microcosm experiment comparing the responses of two grazer species, one caddisfly (Allomyia gnathos) and one mayfly (Baetis bicaudatus), to variation in substrata and risk of predation. We estimated grazer growth rates, algal accrual rates and the per capita effect of grazers on algal biomass in circular flow-through chambers that differed in substratum (artificial moss-covered tiles versus diatom-covered tiles) and predation risk (non-feeding predatory stoneflies present versus absent).
5) Results showed that, although artificial moss-covered tiles provided more food (epiphytic algae biomass - chl-a), only the mayflies grew faster with higher food resources available on the artificial moss compared with those feeding on diatom-covered tiles. Furthermore, algal resource depression was greater on diatom-covered tiles, which suggests that diatoms on bare tiles were more vulnerable to grazing than epiphytes on artificial moss.
6) Although non-feeding predators did not affect the biomass of either grazer species, algal accrual rates were higher in chambers where mayflies were exposed to predation risk, which is consistent with a behavioural trophic cascade. Mayflies also had a higher per capita impact on algal biomass in the absence of predatory stoneflies.
7) We conclude that armoured, less mobile and disturbance-vulnerable caddisfly grazers primarily colonise mossy substrata for protection, because we found no evidence that they benefit from the higher epiphytic food supply on moss. However, although disturbance-resistant mayflies can exploit increased food resources provided by moss, in nature they do not aggregate on mossy substrata in preference to diatom-covered mineral substrata.
8) Therefore, classical trade-offs between food acquisition and safety do not explain the observed distributions of caddisflies, which prefer habitats that both are safe and have the best food resources, nor of mayflies, which prefer neither the safest nor the most resource-rich habitats. These results demonstrate that mayflies and caddisflies have evolved different solutions to the problems of foraging under risks of predation and disturbance."

Àlvarez,M and Peckarsky,BL 2014 Cascading effects of predatory fish on the composition of benthic algae in high-altitude streams. Oikos, 123(1)120-128. PDF

Banks,N 1916 A classification of our limnephilid caddice flies. Canadian Entomologist 48: 117-122.
     Describes the genus Allomyia with the key to genera.

Herrmann,SJ; Ruiter,DE and Unzicker,JD 1986 Distribution and records of Colorado Trichoptera. Southwestern Naturalist 31 4, 421-457.
     They note that A. gnathos is found in Gunnison County. Quote from page 438: " Habitat: streams; Altitudinal range: 2713-3616m; Adult collection dates; 19 June to 5 August; Until recently, this species was placed in the genus Imania (Schmid, 1980). This genus and species appears restricted to cold rapid streams of the montane and alpine zones of Colorado."

Peckarsky,BL; McIntosh,AR; Àlvarez,M and Moslemi,JM 2013 Nutrient limitation controls the strength of behavioral trophic cascades in high elevation streams. Ecosphere, 4(9)1-17. PDF
     Abstract: "Indirect effects of predators on primary producers vary over space and time. Key components of the environmental context underlying that variability include the bottom-up supply of resources and the defense, mobility and foraging efficiency of primary consumers. We manipulated key resources that limit primary producers and tested the effects of system enrichment on the strength of top-down interactions between top predators (Salvelinus fontinalis), different types of grazing invertebrates and algae in high elevation streams of Colorado, USA. We added nitrogen and phosphorus to flow-through microcosms powered by stream water and tested the direct effects of chemical cues from brook trout on the behavior of sedentary, predator-resistant (caddisflies) and mobile, predator-vulnerable grazers (mayflies), and the indirect cascading effects of predators on: (1) the biomass of algae mediated by grazer behavior and (2) the impact of grazers on algal biomass accrual. Recognizing the value of whole-ecosystem experiments, we also tested the effects of supplementing nutrients to two headwater fishless streams on the impact of grazers on algae and the performance (growth rates) of four predominant grazer species compared to two adjacent reference streams with ambient (limited) nutrients. In both experiments, algal biomass increased with added nutrients where consumption by grazers was swamped by increased algal accrual due to enrichment. Results of the microcosm experiment were consistent with a context-dependent behavioral trophic cascade whereby predator cues increased the biomass of algae only in treatments with enrichednutrients and mobile, predator-vulnerable grazers (Baetis mayflies). Baetis showed risk-sensitive behavioral responses to fish cues, which resulted in cascading effects on algae only under enrichment. In contrast,behavior of sedentary, predator- resistant caddisflies (Allomyia) was unaffected by predator cues and a cascade was never observed. The whole ecosystem experiment revealed no aggregative responses by grazers but instead, strong developmental responses of all grazer species to nutrient enrichment. Growth rates of grazers increased with mobility, with the highest rates occurring for mobile, predator-vulnerable Baetis mayflies in enriched streams. Our results emphasize the importance of experimentally testing thecontext-dependency of trophic cascades, and are consistent with the hypothesis that nutrient limitation may reduce the strength of trophic cascades."

Ross,HH 1950 Synoptic notes on some nearctic Limnephilid caddisflies (Trichoptera: Limnephilidae). American Midland Naturalist 43 (2) 410-429.
     Described as Imania gnathos.

Ruiter,DE and Nishimoto,H 2019 New species of Allomyia Banks from the Western United States (Trichoptera: Apataniidae). Zoosymposia, 14(1), pp.273-288. PDF
     Abstract: "Six new Allomyia species from the western United States are described: Allomyia kondratieffi sp. nov., Allomyia leei sp. nov., Allomyia meachamensis sp. nov., Allomyia sarahae sp. nov., Allomyia sheldoni sp. nov., Allomyia whatcomensis sp. nov. The majority of these species were collected from small headwater, high altitude streams on relatively isolated mountain ranges. These species bring the number of known North American Allomyia to 18. Additional notes on state/county distribution records, taxonomic problems, species diagnostics and adult emergence periods for the 18 North American species are provided."

Schmid,F 1980 The insects and arachnids of Canada, part 7, The genera of Trichoptera of Canada and adjacent regions. Ontario, In French. 296pp
     Schmid moved Imania gnathos to the genus Allomyia.

Brown, WS 2004 Trichoptera or Caddisflies of Gunnison County, Colorado, USA