Montana Field Guide

Trichoptera is the largest and most diverse order of insects that is primarily aquatic, with about 13,000 species worldwide (Holzenthal et al. 2007, de Moor and Ivanov 2008). The roots of Trichopteran lineages date back to at least the middle of the Jurassic period (Holzenthal et al. 2007). Caddisfly larvae are vital contributors to aquatic food webs and their presence is often used when assessing water quality. Caddisflies are most closely related to Lepidoptera (butterflies and moths), and they share characteristics such as spinning silk. Adult caddisflies are medium-sized insects with tent-shaped wings. They resemble moths, but caddisflies do not have a coiled proboscis and their wings are covered in hairs rather than scales. They tend to be secretive and slow-flying riparian insects (Anderson 1976).

Caddisflies spend much of their life in the water as aquatic larvae and most species build portable, protective cases made from plant material or stones. These cases are incredibly intricate and complex structures, especially for a non-social insect (Holzenthal et al. 2007). Trichopteran larvae have well-developed mouthparts; mandibles of shredders are broad with cutting teeth, while the mandibles of scrapers are more elongated with entire edges. Abdominal gills are present in most species.

Caddisflies typically have five larval instars before pupation (Wiggins 1996). During pupation, the insect’s antennae, legs, and developing wings are free from the body, and characteristics can still be used for identification (Holzenthal et al. 2007). Adult caddisflies are terrestrial and usually dully colored. This order of insects is very diverse and adult body length can range from 1.5mm to 45mm. Unlike Trichopteran larvae, adult caddisflies have reduced mouthparts because they only live from a few days to a couple weeks (Wiggins 1996).

The genus Apatania is one of 18 genera within the Apataniidae family. This family is found in the northern montane regions of North America, Europe, and Asia (Holzenthal et al. 2007). Apataniid larvae live in cool running waters at high elevations and construct their cases from small rocks. All genera within the Apataniidae family have antennae located between the eye and the anterior margin of the head, and have either single or absent abdominal gills (Wiggins 1996).

Larvae from the genus Apatania have a unique absence of the front and center pair of sclerites on the metanotum (3rd thoracic segment; lack metanotal sa1 sclerites). Additionally, the setae on these sclerites are in a line (Wiggins 1996). Apatania larvae measure 7.5mm long, have mandibles with an entire scraping edge, and their heads have many secondary setae (Wiggins 1996). This genus uses rock fragments to build a larval 9.5mm long case that is tapered from front to rear and curved dorsoventrally. Apatania larvae in their final instar prepare for pupation by extending the dorsal edge of the anterior opening so it overhangs the ventral edge. This edge will turn into a hood in pupation, which is characteristic of the genus Apatania.

Neither larvae nor adult descriptions are well-known for A. comosa, and distinctions between this species from other Apatania species are difficult to determine (Chen 1992). Additionally, individual variation occurs often in the genus Apatania, which makes identification even more difficult. Further research into this species should be done to determine unique species characteristics.

Apatania comosa larvae are usually found on rock faces in cold mountain springs or streams (Chen 1992). Some Apatania species in the far north can occur in deep lakes (Wiggins 1996).

Caddisfly adults tend to remain near the emergence site where oviposition occurs. Although dispersal flights are common, they are relatively short and only occur immediately following emergence. Dispersal from emergence sites tends to be negatively correlated with vegetation density (Collier and Smith 1998). In other words, caddisflies tend to disperse shorter distances in dense forest compared with more open areas.

Apatania larvae are scrapers, eating periphyton (algae growing on substrate such as rocks) growing in streams (Wiggins 1996, Holzenthal et al. 2007), and they cling and crawl amongst rocks while doing so (Sueyoshi et al. 2014).

Adult caddisflies usually do not have developed mouthparts and only eat nectar, sap, or nothing during their adult lifespan.

Another Apatania species (A. fimbriata) is known to have glands on its prothorax that secretes a substance that has a paralyzing effect on insect predators such as Rhyacophila larvae (Wagner et al. 1990, Wiggins 1996).

Little is known about the life cycle of A. comosa and more surveys are needed to understand when they emerge as adults. Most caddisflies have a one-year life cycle (univoltine), but some species may need more than one year to fully develop (semivoltine). Some species that are univoltine in lower elevation temperate streams may be semivoltine at higher latitudes or elevations because the growing season is too short for larvae to fully develop (Giersch 2002). Most of their lives are spent underwater feeding and growing.

After pupation, A. comosa transitions from the aquatic to the terrestrial environment. Most caddisflies emerge in late summer, but semivoltine species can emerge at different times of the year. As adults, they use trees as roosting places.

Another Apatania species that occurs on Ellesmere Island, Canada (A. zonella) had far more females compared to males and are thought to reproduce parthenogenetically (Corbet et al. 1966, Wiggins 1996). Similarly, another Apatania species in Denmark suggested that this phenomenon can occur at more southern latitudes (Wiggins 1996).

Freshwater aquatic habitats are one of the most imperiled ecosystems globally because its water collects all the abuses in the entire watershed area (Holzenthal et al. 2007). Cold-water invertebrates are thought to be specialists and are sensitive to changes in aquatic habitat (e.g., flow patterns, streambed substrate, thermal characteristics, and water quality; Green et al. 2022). Forest riparian areas are prone to increases in sediment and temperature when the landscape is disturbed, such as road building and timber harvests, and may make these streams less suitable for cold-water invertebrates (Stagliano et al. 2007). Additionally, researchers have begun studying the effects of climate change on Trichopterans in alpine headwater streams (Brown et al. 2007, Holzenthal et al. 2007), but much more research is needed to understand how these insects will respond.