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).

Neotrichia ersitis is part of the family Hydroptilidae, a group known as the micro-caddisflies because of their small size, 2-3mm long. (Wiggins 1996). Hydroptilidae larvae generally lack gills and all three of their thoracic nota are sclerotized. This family is unconventionally free-living and does not build a case until its fifth and final larval instar. Hydroptilid larvae have been known to leave a silken thread wherever they go (Wiggins 1996). Throughout their fifth instar, the larva’s abdomen enlarges as it stores energy reserves.

Neotrichia is the smallest genus within Hydroptilidae, and Neotrichia ersitis larvae likely only reach 2mm in length! Reliable characters for distinguishing the species from other Neotrichia are not known (Ross 1948, Wiggins 1996). Neotrichia larvae have a long head that narrows slightly, long antennae, and long, slender legs. Final instar larvae build cylindrical cases that taper posteriorly and are up to 2.5mm long.

Neotrichia larvae are very difficult to differentiate from another Hydroptilid genus Mayatrichia, but their cases can help distinguish them with mature specimens. Mayatrichia larvae build their cases out of silk, while Neotrichia larvae build their cases out of fine grains of sand.

Neotrichia ersitis adults are 1.8-2.0mm long and golden-brown in color (Keth 2002). Adult male N. ersitis individuals are distinguishable from other Neotrichia adults by the paired preapical hooks at the tip of the phallus, the laterally ornate sclerotized tip of the subgenital plate, and the lack of secondary setae under the subgenital plate. Confirming the species can also be done through analyzing the male genitalia; for more information about male genitalia characteristics of N. ersitis, see Keth (2002). Adult female N. ersitis have not been described.

Neotrichia larvae inhabit flowing water and are found on rocks in the swifter sections of the river or stream (Wiggins 1996).

Neotrichia larvae mostly graze on fine organic material, such as algae, that are on rocks in the stream. They are likely specialized in their food-gathering habits (Keth 2002).
Adult caddisflies usually do not have developed mouthparts and only eat nectar, sap, or nothing during their adult lifespan.

Despite occupying the same niche, Neotrichia and Mayatrichia larvae have been collected from the same site in Ontario (Wiggins 1996). The co-occurrence between these genera should be further researched in order to understand the relationship between these caddisflies in stream ecosystems.

Most caddisflies have a univoltine (one-year) life cycle, including most Neotrichia species (Houghton 2012). This means larvae typically grow and feed during winter and early spring, pupate in the summer, and emerge as adults in the fall. Some Neotrichia ersitis adult males have been collected on August 1st in Saskatchewan and September 5th in Montana. This data reinforces the likelihood that this species emerges in the fall, but more surveys should be done to further understand the life history of N. ersitis. Many caddisflies are known to be multivoltine and can sustain pre-pupal diapause in unfavorable conditions like drought (Wiggins 1996). Additionally, the short summers within this species’ distribution may not provide enough time for maturing, so they may live for more than one year.

Caddisfly adults tend to remain near the emergence site where oviposition occurs, meanwhile roosting on trees. 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.

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.