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 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).

Neophylax sinuatus is in the Trichopteran family Uenoidae. This family has 70 described species worldwide, and its larvae can be distinguished from other caddisflies in several ways. Uenoidae larvae have notches on the anterior side of their mesonotum, a wedge-shaped sclerite under their head, a prosternal horn, a membranous border on their labrum, and antennae halfway between their eyes and the anterior end of their head (Wiggins 1996). Additionally, larvae are plump in dorsal view, with the posterior half of their pronotum being broader than the anterior half. About half of the species in Uenoidae family belong to the Neophylax genus.

There are 21 species of the Neophylax in North America, with only four living in the mountains of western North America. Neophylax larvae have a long head and a pronotum that narrows towards the head. All larvae from Neophylax have single abdominal gills and measure up to 15mm long (Wiggins 1996).

Neophylax larvae build short and thick cases made from coarse rock fragments. The cases measure up to 15mm long. These cases resemble those made by the genus Goera, but generally have ~2 large ballast stones on each side compared to Neophylax cases which have >2 smaller ballast stones (Wiggins 1996).

Very little information is available on the descriptions of the larva, pupa, and adult stages of Neophylax sinuatus.

The specific habitat N. sinuatus larvae select for is not known, but some information is available for the genus. Neophylax is the only genus within the family Uenoidae that is not restricted to cold, rapid headwater streams (Wiggins 1996). Many species occur further downstream in slower and warmer water. Several species may occupy a stream, with different species selecting for particular habitats, sections, or longitudinal zones of the ecosystem (Wiggins 1996, Englmaier et al. 2020). All Neophylax larval species feed on algae on rocks. Larvae form large pupal aggregations under rocks (Vineyard 1990, 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.

All Neophylax larval species graze on the algae found on rocks. Larvae have a specialized set of mandibles that lack teeth designed to scrape these tiny particles off rocks (Wiggins 1996).

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

Longitudinal zonation is characteristic of the genus Neophylax, which often allows for sympatry (multiple species living in the same stream) among different Neophylax within a stream ecosystem. In the eastern United States, life-cycle modification allows for two Neophylax species to occur in the same habitat. Neophylax nacatus larvae feed during the winter and emerge as adults in the autumn, while N. ornatus larvae feed from summer until fall and emerge as adults in the spring (Mackay 1969, Wiggins 1996).

Little is known about Neophylax sinuatus, but this species is likely spending most of its life feeding in a stream as larva before emerging as a winged adult in the late summer. Most caddisflies have a univoltine (one-year) life cycle. Information from Neophylax species in western North America indicated that they spend the autumn through early summer as larvae. Late instar larvae secure their cases to rocks, seal off the case’s entrance, and undergo metamorphosis (Wiggins 1996). Adults emerge several weeks later in late summer (Beam and Wiggins 1987, Wiggins 1996). In intermittent streams, many Neophylax species sustain pre-pupal diapause until after summer drought, thus delaying adult emergence and breeding (Wiggins 1973, 1996). Larvae can survive up to six months during periods of high-water temperatures or reduced flow using this method. As adults, they use trees as roosting places and live for a few weeks.

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). 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.