An Annotated List of the Mayflies, Stoneflies, and Caddisflies of the Sand Creek Basin, Great Sand Dunes National Park and Preserve, Colorado, 2004 and 2005

By Robert E. Zuellig¹, Boris C. Kondratieff², David E. Ruiter³, and Richard A. Thorp¹

¹U.S. Geological Survey, Denver Federal Center, MS 415, Denver, CO 80225
²Department of Bioagricultural Sciences and Pest Management, Colorado State University, Fort Collins, CO 80523
³6260 South Grant Street, Centennial, CO 80121

Introduction

In the last decade, several federal agencies have emphasized the need for developing formal biological inventory and monitoring programs. These programs document both historical and current biodiversity and assess the impacts of natural and human-induced environmental disturbance. Examples of such programs include the National Park Service Inventory and Monitoring Program, the National Water Quality Assessment (NAWQA) program of the U.S. Geological Survey, the Environmental Monitoring and Assessment program (EMAP) of the U.S. Environmental Protection Agency, and the National Forest Inventory and Analysis program of the U.S. Forest Service. Inventories of flora and fauna associated with literature reviews are typically the first phase of these programs and represent an extensive point-in-time effort to determine the spatial distribution of species. Often, based on these inventory data, a followup monitoring program is implemented where study sites of special interest are determined, and more intensive sampling is performed to detect temporal changes in biota.

Inventories of aquatic insect communities are meaningful for several reasons. First, aquatic insect taxa have varying degrees of sensitivity to environmental stressors (for example, siltation, flooding, pollution), which make them excellent indicators of water quality. Second, aquatic insects play a crucial role in aquatic food webs by processing (feeding on) algae and leaf litter and by serving as an important food source for fish and other aquatic predators. Third, most aquatic insect species spend the adult part of their life cycle in the terrestrial environment, subsidizing terrestrial food webs and possibly being an important food source for bats, birds, and riparian spiders. Additionally, aquatic-insect inventories are critical to expanding general entomological knowledge because the distribution and ecology of many aquatic-insect species are still poorly known.

The U.S. Geological Survey, in conjunction with the Great Sand Dunes National Park and Preserve and its cooperators, did an extensive inventory of certain targeted aquatic-insect groups in the Sand Creek Basin, Great Sand Dunes National Park and Preserve, to establish a species list for future monitoring efforts. Study sites were established to monitor these groups following disturbance events. Such potential disturbances may include, but are not limited to, chemical treatment of perennial stream reaches to remove nonnative fishes and the subsequent reintroduction of native fish species, increased public use of backcountry habitat (such as hiking and fishing), and natural disturbances such as fire. This report is an annotated list of the mayflies, stoneflies, and caddisflies found in the Sand Creek Basin, Great Sand Dunes National Park and Preserve, 2004 and 2005.

The primary objective of the study was to qualitatively inventory target aquatic-insect groups in perennial streams, and selected unique standing-water habitats, such as springs, and wetlands associated with the Sand Creek Basin. Efforts focused on documenting the presence of aquatic-insect species within the following taxonomic groups: Ephemeroptera (mayflies), Plecoptera (stoneflies), and Trichoptera (caddisflies). These insect orders were chosen because published species accounts, geographic distribution, and identification keys exist for many Colorado species. Given the extent of available information for these groups, there existed a potential for identifying new species and documenting range extensions of known species.

Study Area

This study was conducted in the Sand Creek Basin within the boundaries of the Great Sand Dunes National Park and Preserve, Saguache County, Colorado (fig. 1). The Preserve part is directly adjacent (northeast) to the Great Sand Dunes National Park, along the western flank of the Sangre de Cristo Range of the Rocky Mountains. The alpine lakes and headwater streams of the Sand Creek Basin are the primary source areas for the ground-water stores beneath the Great Sand Dunes National Park.

Sand Creek originates at an elevation of 4,124 meters and flows approximately 19 kilometers before ultimately terminating in the dune field of Great Sand Dunes National Park. The vegetation of the basin is typical of the southern Rocky Mountains (fig. 2). Higher elevation areas are dominated by alpine tundra and spruce fir communities. Middle elevations have abundant aspen, whereas the lower elevations are dominated by piñon juniper communities near the dune field.

Methods

Site Selection

The distribution of aquatic insects is highly correlated with elevation in Rocky Mountain streams; therefore, sites were selected approximately every 300 meters in elevation from the outlet of Upper Sand Creek Lake (3,581 meters) to the bottom of the basin (2,464 meters) (fig. 2). In addition to the main stem of Sand Creek, selected perennial tributaries and associated seeps, ephemeral streams, and woodland ponds were sampled (table 1). Twenty-one permanent sampling stations were established along this elevation gradient and geo-referenced using a hand-held Global Positioning Unit (fig. 2).

Collection Techniques

Sampling began in the spring of 2004 and continued through October 2005 with monthly or bimonthly site visits. Effort was made to sample spring, summer, winter, and fall to capture the seasonality associated with the aquatic-insect emergence of this region. All sampling required extended backcountry travel. Given these challenging logistics, several sampling methods typically used to collect aquatic insects were modified for backcountry conditions.

Immature stages of insects were collected from each unique habitat type at each site (such as undercut bank, riffle, run, pool, leaf pack, woody debris) using a D-frame kick net (1-millimeter mesh). The contents of the net were placed into a white plastic pan and sorted in the field. A series of each taxon was removed from the pan and preserved in 80-percent ethanol. Species identification of many aquatic insects is possible only with adult male forms; therefore, mature nymphs that appeared ready to emerge, and pupating caddisflies were transported to a laboratory at Colorado State University (Fort Collins, Colo.) and reared to adulthood.

Adult insects were collected at each site using a beating sheet, sweep net, or by hand picking individuals from exposed substrate or riparian vegetation and then preserved in 80-percent ethanol. Mayfly subadults (subimagos) collected in the field were kept alive in 250-milliliter plastic containers with 1-millimeter mesh screens and stored in a soft cooler until their final molt to adulthood (imagos), and then preserved in 80-percent ethanol. Specific identification of some stonefly groups requires the use of developed eggs and extruded male genitalia (adeagus); therefore, adult stoneflies collected in the field (Isoperla, Suwallia) also were kept alive until further processing in the laboratory. Pan and light traps also were used on several occasions with limited success, probably because of the cool temperatures associated with the relatively high elevations of the basin. Additionally, interception (malaise) traps were used adjacent to the stream just downstream from Upper Sand Creek Lake and just downstream from Lower Sand Creek Lake from June 2005 until October 2005. Interception trap collection containers were replaced about every 2 to 3 weeks during the sampling period.

Sample Processing

All invertebrate samples were transported to Colorado State University for further sorting and identification. Live insect larvae were transported in aerated coolers to the aquatic-insect rearing facility at Colorado State University and were kept alive until emergence. Larval cast skins left behind after emergence of mayflies and stoneflies reared in the laboratory were collected to help associate the immature stages with adult forms. All specimens reared in the laboratory were preserved in 80-percent ethanol and later were identified to the lowest possible taxonomic resolution. Specimens ultimately were deposited in the C.P. Gillette Museum of Arthropod Diversity at Colorado State University as a permanent loan from the National Park Service (Phyllis Pineda Bovin, Great Sand Dunes National Park and Preserve, oral commun., 2004). Deposited material was labeled using National Park Service approved labels and entered into the Automated National Catalogue System (ANCS+) software Park Service database (ver 6.3.1, R:discovery Software, Inc.) by National Park Service staff.

Results and Discussion

Nearly 4,200 specimens were examined from 71 site visits. Of the specimens examined, 70 species were identified from 47 genera and 19 families. The caddisflies were the most diverse with 31 species, followed by the stoneflies with 24 species, and the mayflies with 14 species (table 2). Below is a brief introduction to each order and a synopsis of the taxa collected from the Sand Creek Basin, Great Sand Dunes National Park and Preserve, Saguache County, Colorado, during 2004 and 2005.

Ephemeroptera (Mayflies)

The Ephemeroptera are the most primitive order of aquatic insects (Merritt and Cummins, 1996). Mayfly immatures, or nymphs, can be distinguished from other aquatic insects that have an incomplete metamorphosis (hemimetabolous) by the presence of two or three tails (caudal filament) at the end of the abdomen and one claw at the end of each leg. Gills are attached to various segments on the sides of the abdomen, either as flattened plates or filaments. Excluding caudal filaments, body length can range from 2 to as much as 35 millimeters. Immature mayflies occur in diverse lotic (flowing waters, streams, rivers) and lentic (standing waters, ponds, lakes, reservoirs) habitats. However, a greater diversity typically is found in lotic habitats. Most mayfly nymphs acquire their food as collector-gatherers of plant detritus or scrapers of algae. A few species, however, are specialized, fine-particulate organic-matter (FPOM) filter-feeders or carnivores. Shredders of coarse-particulate organic matter (CPOM) are very poorly represented in this insect order. Microhabitat occurrence is reflected more distinctly in the body form of nymphs than in that of any other order. Some species have a streamline (fusiform) body shape that enables them to swim in rapid water, whereas others are flattened dorsoventrally to closely adhere to rock surfaces. Other groups construct burrows in the substrate with their mandibles and undulate their gills to create respiratory and feeding currents. Others are adapted for climbing among accumulations of organic material, silty backwaters, or plant beds.

Most mayflies of temperate regions have a 1-year life cycle (univoltine), the majority of which is spent under water. Arial adults do not feed and typically live from 1 hour to several days. This variability depends on weather conditions and each species’ specific biology. Adults are easily distinguished by the presence of usually two pairs of membranous wings; the front wings are larger and triangular in shape, and the hind wings are much smaller or even absent. The antennae are bristle-like, and two or three long-segmented caudal filaments extend beyond the end of the abdomen. Most mayfly adults have two distinct winged stages. The subadult (subimago) is the first winged stage that occurs after these animals molt from the nymphal stage. Subimagos then typically undergo a second molt to reach the final adult stage (imago). Adult mayflies often form enormous nuptial flights during which mating occurs. This swarming behavior can take place over water or remote from a body of water, and at various times of the day or night. The eyes of the male imago are larger than the females, which is apparently an adaptation for better visual acuity during aerial mating. Mated females return to the water to oviposit. See Brittain (1982; 1990) for a thorough review of mayfly biologies.

Currently, approximately 676 species within 21 families are recognized from North America. McCafferty and others (1993) and Durfee and Kondratieff (1994) provide distributional information for the mayflies known from Colorado and collectively report 101 species. McCafferty and others (2004) and McCafferty (1996) provide a comprehensive index of the mayfly species of North America.

Ameletidae (Minnow Mayflies)

Larvae usually are found in small, cool, fast-flowing streams among rocks. Some species are confined to very small brooks, often congregating in pool areas. Nymphs are strong swimmers and feed by scraping algae, using a modified mouthpart consisting of a pectinate comb of spines, or diatom rake, to feed on periphyton or algae (Ward and others, 2002). There is usually only one generation per year (univoltine) associated with species’ of this family. Some species of the genus Ameletus in Eastern North America may be able to reproduce without the presence of males (parthenogenetic). Three species were collected during this survey (table 2). Ameletus sparsatus McDunnough was the common ameletid; whereas Ameletus cooki McDunnough and Ameletus velox Dodds were rare, only being collected and reared from one site each. Ameletus cooki is considered rare in collections from Colorado. Several Ameletus nymphs were collected from study sites in the basin; however, adult males are needed for species identification and are rarely collected in the field. When found, representatives from most sites were brought back to the laboratory for rearing but unfortunately often only females emerged in the laboratory. It is likely that A. cooki and A. velox are more common in the Sand Creek Basin than records indicate.

Baetidae (Small Minnow Mayflies)

Nymphs of this family are found in a wide variety of aquatic habitats. They are often the only mayflies present in extreme environments such as high-elevation streams, the sources of springs, or mildly polluted waters (Ward and others, 2002). They are considered good swimmers, darting in short spurts from one spot to another. They are often the most abundant mayflies of many North American streams. The species of the genus Baetis collectively occupy an extremely wide range of stream habitats. The genus Callibaetis is primarily a standing-water genus, but some species also occur in the backwaters or quiet margins of running waters. Most members of the family are collector-gatherers or scrapers. Many of the species found in flowing-water habitats apparently have two generations per year (bivoltine), others only one. Baetis tricaudatus Dodds was the abundant baetid species found in most of the streams of the Sand Creek Basin. Baetis bicaudatus Dodds also occurred at many stream sites but was most common at higher elevations. These two species co-occurred at several sites (table 2). Callibaetis ferrugineus hageni Eaton was collected only from one woodland pond adjacent to Sand Creek, but this species probably is more common than recorded in this survey in other lower elevation lentic habitats that were not sampled.

Ephemerellidae (Spiny Crawler Mayflies)

Nymphs of this family occur in almost all types of flowing water. Some species occur in steep-gradient segments of streams in high elevations, whereas others occur in silty microhabitats at lower elevations (Ward and others, 2002). Some groups also are found in the standing waters of lakes and wetlands. Nymphs crawl about and are well camouflaged with their environments. Most species are considered collector-gatherers of detritus or scrapers of algae, but some species of the genus Drunella have been reported to be partially predaceous. Interestingly, these nymphs use a unique defensive behavior where they arch their abdomens and raise their three tails in a scorpion-like posture, which apparently acts as a deterrent to some macroinvertebrate predators. Most species have one generation per year. This family was well represented in the Sand Creek Basin, with four species being collected during this study. Drunella coloradensis (Dodds), Drunella doddsii (Needham), and Ephemerella dorothea infrequens McDunnough were relatively common and widely distributed, whereas Serratella micheneri (Traver) was restricted to the lowest two sites in the basin (table 2).

Heptageniidae (Flatheaded Mayflies)

Heptageniids are perhaps the most characteristic group of all mayfly families found in flowing water (Ward and others, 2002). The nymphs are dorsoventrally flattened and generally structurally adapted for high gradient mountain streams. Most species are restricted to running waters, but a few also inhabit the wave-swept margins of lakes. Genera such as Epeorus and Rhithrogena usually are restricted to cool, fast mountain streams. Most heptageniids are scrapers, removing attached algae and other particles from rock surfaces; a few are collector-gathers or predators. The numerous North American species have one to two generations per year. Heptageniids were well represented within the basin, and at least four species were collected. Epeorus longimanus (Eaton) and Epeorus deceptivus (McDunnough) co-occurred at several sites (table 2). Rhithrogena robusta Dodds was restricted to sites above 3,000 meters. Cinygmula ramaleyi (Dodds) was common in the main stems of Sand Creek and Little Sand Creek. Several Cinygmula nymphs also were collected from the smaller tributaries in the basin, but adult males are necessary for specific identification. Nymphs collected in the smaller tributaries are likely C. ramaleyi.

Plecoptera (Stoneflies)

Nearly all species of Plecoptera (stoneflies) occur exclusively in streams, and most are restricted to cold-water habitats (Baumann, 1979; Stewart and Stark, 2002). Morphologically, the nymphs usually have cylindrical or flattened bodies; a head with long, thin antennae; wing pads (structures containing developing wings) on the thorax of more mature individuals; three pairs of segmented legs, each with two terminal claws; and two long, thin caudal filaments at the end of the abdomen. Some species can have either simple or branched gills on the thorax or abdomen. Most stonefly nymphs are herbivores, feeding principally on plant detritus (see references cited in Stewart and Stark, 2002). Even the young nymphs of many carnivorous species first feed on fine detritus before later switching to animal prey. Mature nymphs range in length from a few millimeters to more than 5 centimeters. Although some species emerge in autumn, most stoneflies transform to adults in spring or early summer. However, winter stoneflies typically emerge as soon as openings appear in the ice covering on streams (late winter, early spring). The dark-colored adults can be easily detected on the lighter backgrounds of snow-covered streambanks.

Adult stoneflies can be distinguished from other insects that undergo incomplete (hemimetabolous) metamorphosis by the long, thin antennae and by both pairs of membranous wings being positioned flat against the abdomen when not in use. These wings usually have distinctive vein patterns. The hind wings are usually expanded posteriorly to fold like a fan; hence the name Plecoptera, or “pleated wing.” Some groups of adult stoneflies have reduced wings or even lack wings. Additionally, most species have two thin caudal filaments that project from the end of the abdomen. A remarkable behavior of adult stoneflies is the two-way communication behavior between sexes called drumming. Males tap, rub, or scrape their abdomens upon various substrates such as tree branches, leaves, or rocks. The female subsequently detects this vibration and responds by drumming, ultimately revealing her location to the male. Remarkably, the drumming pattern amplitude, frequency, and or duration often are species specific (Stewart, 1997).

About 650 species within nine families of Plecoptera are known from North America. Baumann and others (1977) provide useful taxonomic keys to the species that occur in the Rocky Mountains, and Kondratieff and Baumann (2002) provide a recent review of the stoneflies of Colorado reporting 86 species. Stark and Baumann (2005) provide an index listing of all North American species by Province or State.

Capniidae (Small Winter Stoneflies)

This family is composed of relatively small specimens and contains many that emerge during the winter and early spring. The numerous species within this family are most common in small streams. Nymphs usually are found in leaf packs or accumulations of woody debris and develop most rapidly during the coldest water temperatures of winter (Stewart and Stark, 2002). The early instars of these stoneflies diapause or cease metabolic activities in the sub-streambed surface (hyporheic zone) of the stream during warmer months. Most species of capniids are detritus shredders. The dark-colored emerging adults often can be seen crawling across the snow during winter or early spring. Capnia gracilaria Claassen and Eucapnopsis brevicauda Claassen primarily were found at the higher elevation sites, whereas Capnia confusa Claassen and Utacapnia logana (Nebeker and Gaufin) were collected at the lower elevations (table 2). It is likely there are additional capniid species in the Sand Creek Basin at the mid- to higher elevation sites that were difficult to access during the winter months.

Chloroperlidae (Green Stoneflies)

Most species of this family are found only in clean, cool streams of mountainous areas (Stewart and Stark, 2002). Nymphs are small, generally elongate or thin, lack gills and typically inhabit the hyporheic zone in the interstitial spaces between substrate particles below the streambed. Some species reside at considerable depths vertically in the substrate and laterally under or within streambanks. The western genus Paraperla is a collector-gatherer of detritus and an algae scraper. Other genera are predaceous on other aquatic insects (often midges). Adults are recognized by their slender bodies and yellow or green coloration. Emergence typically occurs in spring or summer. Five species were collected during this survey. Sweltsa lamba (Needham and Claassen) and Sweltsa borealis (Banks) co-occurred at several sites throughout the basin (table 2). Sweltsa coloradensis (Banks) was collected only at two sites, one just downstream from Lower Sand Creek Lake and another on the main stem of Sand Creek 5.2 kilometers downstream from the Little Sand Creek confluence. Plumiperla diversa (Frison) was restricted to main-stem sites. Lastly, Suwallia pallidula (Banks) was collected at multiple sites within the basin (table 2).

Leuctridae (Rolled-Wing Stoneflies)

Nymphs of this family occur in a variety of lotic habitats from intermittent streams and springs to small perennial streams and seeps. They are associated primarily with leaf packs, woody debris, or mineral substrates. Nymphs are considered shredder-detritivores. Adults of some species emerge between late winter and early summer. Paraleuctra vershina Gaufin and Ricker was collected throughout the Sand Creek Basin, whereas Perlomyia utahensis Needham and Claassen was most common in or near Little Sand Creek (table 2). The latter species is considered rare in collections from Colorado; however, Kondratieff and Baumann (2002) report that Perlomyia utahensis probably is more common than records indicate because it often is associated with higher elevation habitats that rarely are sampled.

Nemouridae (Nemourid Stoneflies)

Nymphs of this family occur in a wide range of aquatic habitats, from seeps and springs to lakes. In lotic habitats, some species are found in large rivers, whereas others are restricted to small streams at higher elevations. Nymphs typically occur in leaf packs and woody debris, but they also can be collected in rocky areas. Life cycles vary from 1 to 2 years. Most adults are recognized by having highly reduced tails (cerci) and a unique X-pattern of veins on the front wings. Emergence occurs typically in the spring, but some species also can emerge in the winter and fall. This stonefly family was the most diverse in this study, with eight species being collected in all. Malenka coloradensis (Banks) and Malenka flexura (Claassen) co-occurred at several sites and were well distributed across all stream sites (table 2). Amphinemura banksi Baumann and Gaufin, Podmosta decepta (Frison), Prostoia besametsa (Ricker), and Zapada cinctipes (Banks) were collected at a few sites. Zapada frigida (Claassen) and Zapada oregonensis (Claassen) consistently co-occurred in Little Sand Creek (table 2). Zapada oregonensis typically was found at higher elevations sites.

Perlidae (Common Stoneflies)

The large and distinctively patterned yellow and brown nymphs of perlid stoneflies can be found in all types of intermittent and perennial streams. Members of this family inhabit warmer waters than most other stonefly families. Nymphs commonly are associated with large loose rocks, but they also use leaf pack and woody debris habitats. The nymphs are predaceous, feeding largely on other aquatic insects. Life cycles range from 1 to 3 years, with most adults emerging between late spring and late summer. Adults often are attracted to lights near streams. Hesperoperla pacifica (Banks) was the only perlid collected in the Sand Creek Basin and was common throughout most of the main-stem Sand Creek sites (table 2).

Perlodidae (Perlodid Stoneflies)

Nymphs of this family are medium to moderately large-sized and primarily predaceous (Ward and others, 2002). If gills are present, they are simple (unbranched) and usually are restricted to the body (thorax) and neck regions. Most species are restricted to cool, swift-flowing, mountain streams with rocky bottoms, but some are restricted to large, silty, western rivers. Some uncommon species are found only in the splash zones of seeps. All species apparently have a single generation per year. Emergence is generally in the spring, but some species also emerge in the fall. The eggs of several species can be dormant (diapause) for as long as 5 to 7 months. Three species were collected from the Sand Creek Basin. Isoperla sobria (Hagen) and Megarcys signata (Hagen) primarily were found in the larger stream sites at higher elevations, whereas Kogotus modesta (Banks) was found in the smaller stream sites (table 2).

Taeniopterygidae (Willow Flies)

Nymphs of this family can be found in habitats ranging from small streams and seeps to large rivers (Stewart and Stark, 2002). Nymphs are leaf shredders and usually are associated with leaf packs. The life cycle of members of this family have one generation per year (univoltine). Some eastern species emerge in winter and early spring; whereas most western species typically emerge in spring or early summer. Six species are known from Colorado (Kondratieff and Baumann, 2002). Only one species, Taenionema pallida (Banks), was collected during this survey from a couple of sites (table 2). This species probably is more widespread within the basin because peak emergence typically is earlier in the year before most sites were accessible. One Taenionema nymph was collected at the low-elevation site, which also is probably T. pallida.

Trichoptera (Caddisflies)

Trichoptera (caddisflies) inhabit a wide range of permanent and temporary aquatic habitats including streams, rivers, springs, seeps, ponds, and lakes (Wiggins, 1996). Caddisfly larvae collectively occupy a diverse array of habitats and feeding types. Wiggins and MacKay (1978) attribute the high ecological diversity of this group or niche segregation to the use of silk (secreted from labial glands) by the larvae. The use of silk by these larvae has significantly enhanced the diversity of their protective cases, retreats, and FPOM capture nets, ultimately leading to the spatial partitioning of habitats. For example, differences in capture net mesh sizes in net-spinning groups enables segregation of food particles of different sizes between closely related species. Trichoptera larvae are highly diverse in their feeding modes (for example, collector-filterers, predators). Several groups are highly specialized filter-feeders that use silk capture nets, the size and shape of which are species specific (Wallace and Merritt, 1980). Rarely, cases may be formed of silk alone, but silk is most commonly used to cement various materials (for example, sand, leaf fragments) together to form a rigid and protective case. Cases may be fixed or portable, but in either situation larvae rarely exit these structures. Although some species are considered “free living” and “caseless,” caddisflies are holometabolous (complete metamorphosis) and eventually construct a case in which they undergo pupation. Most caddisflies have five larval instars (or between molt stages). Fifth, or final, instar larvae construct a pupal case in “free living” species or, for species with cases, seals itself within the larval case to undergo pupation or transformation to the adult stage. This pupal stage lasts only 2 to 3 weeks in most species, and in temperate areas most species are univoltine or require 1 year to develop from egg to adult.

Morphologically and during flight, adult caddisflies resemble moths except that instead of having scales, their wings are covered with fine hairs so the order is named “hairy wing” or Trichoptera. Adults possess all the necessary functional mouthparts of an insect, thus allowing them to drink water and nectar. Adults usually are diurnal or nocturnal and often live for several weeks. As compared to mayflies and stoneflies, most adult caddisflies are strong fliers and thus can disperse greater distances than the latter groups.

Approximately 1,400 caddisfly species are known from North America (Wiggins, 1996). Wiggins (1996) provides generic keys and corresponding ecological data for all North American larvae. Herrmann and others (1986) reviewed the distribution of caddisflies in Colorado and reported 176 species. Morse (1993) provides a checklist of the North American species and Morse and others (2004) reports on the caddisflies of the world.

Brachycentridae (Humpless Case Makers)

These larvae are unique among all portable case makers in that they lack spacing humps on the top and sides of their upper abdomen. Larvae are filter-feeders that attach themselves to streambed substrate (such as cobbles, woody debris) and filter by extending their hairy legs beyond the front of their cases to trap small food particles. Some species make four-sided “log cabin”- style cases, and these species often are found at high densities on substrates. Both larvae and adults are relatively small, and adults are distinctly colored black and white. Brachycentrus americanus (Banks) was the only species collected and appears to be restricted to the main stem of Sand Creek downstream from the Little Sand Creek confluence.

Glossosomatidae (Saddlecase Makers)

Larval saddlecase makers are found in streams where they graze on algae growth on exposed cobble surfaces. Their common name derives from the tortoise-shell-style case of sand that they construct. Pupae sequester themselves within this case by sealing off both ends and attaching the case to streambed rocks with silk. Life histories of western North American species appear to be one generation per year. Adult Anagapetus debilis (Ross) and Glossosoma verdona Ross were collected at one site on the main stem of Sand Creek, whereas Glossosoma larvae were collected at several additional sites (table 2).

Hydropsychidae (Common Netspinners)

The Hydropsychidae, or net-spinning caddisflies, are a dominant group of aquatic insects in running-water habitats throughout the world. Larvae are considered important components of macroinvertebrate communities because of their high abundance and subsequent considerable biomass. Larvae construct retreats by cementing stones and vegetative debris to streambed substrata with silk. At the upstream openings of their retreats, these larvae spin a silken net. This net is suspended perpendicular to the direction of streamflow and is used to filter food items drifting downstream. Larvae typically occupy the rear or downstream end of the retreat, but occasionally visit the net to consume captured materials. Interestingly, each genus constructs a net of a specific mesh size and shape. Species living in torrential headwater habitats characteristically construct nets with large mesh sizes to ease the passage of the rapidly moving water and to target the larger organic particles associated with headwater streams (such as leaves, large woody debris, and other insects). Species that live in large rivers have nets of a very fine mesh to capture the finer food particles typical of downstream reaches of these environments. Only one adult hydropsychid taxa, Arctopsyche inermis Banks, was collected during this study. Several Arctopsyche larvae were collected at most sites. Typically A. inermis is restricted to higher elevations, whereas A. grandis Banks is found at lower elevations. It is likely that the larvae collected at the lower elevations are A. grandis.

Lepidostomatidae (Lepidostomatid Case Makers)

Most species of this family are associated with small, cold streams and sometimes large rivers. Larvae make cases of various shapes using rock and plant materials. These animals as shredders feed mostly on decaying plant material, and accordingly, larvae usually are found sprawling among leaves and debris in areas of reduced flow in streams. Adults of Lepidostoma cascadensis (Milne) and Lepidostoma unicolor (Banks) were collected from several stream sites in the Sand Creek Basin (table 2) but never co-occurred. Unidentifiable Lepidostoma larvae also were collected from several main-stem Sand Creek sites.

Limnephilidae (Northern Case Makers)

Larvae of this diverse family occupy a wide range of standing- and running-water habitats (Wiggins, 1996). These larvae construct cases of rock and(or) debris for protection and feed by shredding leaves or scraping algae. Life cycles vary and can range from 1 year to several years. Both the larvae and adult forms of this family are among the largest caddisfly taxa in North America. Adults often exhibit unique and strikingly beautiful patterns of hairs on their wings. This was the most diverse family of aquatic insects identified during this survey with 12 species collected. Hesperophylax was the most common genus (table 2). Several species, Amphicosmoecus canax (Ross), Asynarchus nigriculus (Banks), and Psychoglypha subborealis (Banks) were associated with standing-water habitats. Many other limnephilid species, Chyranda centralis (Banks), Dicosmoecus atripes (Hagen), Ecclisomyia conspersa Banks, and Hesperophylax consimilis (Banks) were associated with flowing waters. Onocosmoecus unicolor (Banks) apparently was associated only with the lower elevations of the basin. Hesperophylax designatus (Walker), Limnephilus moestus Banks, and Psychoglypha ormiae (Ross) were collected at the higher elevation sites, whereas Hesperophylax occidentalis (Banks) was common. Only larvae of the genus Homophylax were collected from one small tributary in the upper part of the Sand Creek Basin (table 2).

Philopotamidae (Fingernet Caddisflies)

Larvae of this caddisfly family occur only in riffle areas of streams (Wiggins, 1996). In a manner similar to the hydropsychid caddisflies, larvae spin nets of very fine mesh to capture food particles. In fact, the meshes of the nets of these filter-feeders are the finest of all net-spinning caddisflies. Like many caddisfly families of the Rocky Mountains, most species in this family produce one generation per year. Only larvae of the genus Dolophilodes were collected, and they were collected at nearly the highest and lowest elevation sites. Adult males are necessary for specific identification. Currently, only Dolophilodes aequalis is known from Colorado mountain streams (Ward and others, 2002).

Rhyacophilidae (Free-Living Caddisflies)

As their common name suggests, larvae of the family Rhyacophilidae do not use a portable case or retreat. The genus Rhyacophila is quite diverse, with more than 100 species found in the cool waters of North America (Wiggins, 2004). Larvae are mobile predators, using large hooks at the end of their abdomen to anchor themselves to substrate while they hunt other aquatic macroinvertebrates. Eight species were identified, many of which co-occurred at several sites (table 2). The most common species was Rhyacophila verrula Milne. Rhyacophila alberta Banks, R. brunnea Banks, R. coloradensis Banks, R. hyalinata Banks, R. pellisa Ross, and R. vao Milne also were collected in addition to larvae from the R. siberica group.

Uenoidae (Uenoid Case Makers)

Larvae of this family construct strongly tapered cases of rock fragments and feed on algae and other plant materials. Three species were collected from the Sand Creek Basin during this study. Neothremma alicia Dodds and Hisaw was restricted to small, unnamed tributaries in the basin; whereas Neophylax splendens Denning and Oligophlebodes minutus (Banks) were collected from Sand Creek at sites lower in the basin.

Acknowledgements

Special thanks to Fred Bunch, Phyllis Pineda Bovin, Andrew Valdez, and the additional National Park Service staff and cooperators who assisted with field operations at Great Sand Dunes National Park and Preserve during this study. Additionally the authors thank Oliver Cox, Colorado State University, and Jim Bruce, U.S. Geological Survey, for providing extraordinary field assistance. Nicole Vieira, Colorado Division of Wildlife, provided assistance in the earlier stages of the preparation of this report. Breton Bruce and Daren Carlisle, U.S. Geological Survey, provided suggestions that improved earlier versions of this manuscript. Jean Dupree, U.S. Geological Survey, created all figures for this document.

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