Waterfalls as a reservoir for caddisfly larvae (Insecta, Trichoptera): exploring a poorly known habitat

479 Waterfalls as a reservoir for caddisfly larvae (Insecta, Trichoptera): exploring a poorly known habitat Darha Solano-Ulate1,2 , Monika Springer1,2,3 1 Escuela de Biología, University of Costa Rica, San José, Costa Rica 2 Museo de Zoología, Centro de Investigación en Biodiversidad y Ecología Tropical (CIBET), University of Costa Rica, San José, Costa Rica 3 Centro de Investigación en Ciencias del Mar y Limnología (CIMAR), University of Costa Rica, San José, Costa Rica Corresponding author: Darha Solano-Ulate ([email protected]) Copyright: © Darha Solano-Ulate & Monika Springer. This is an open access article distributed under terms of the Creative Commons Attribution License (Attribution 4.0 International – CC BY 4.0). Research Article Abstract Waterfalls have not been thoroughly studied as a habitat for freshwater macroinvertebrates, although they appear to be an exclusive environment for taxa with traits suited to these unique physical habitat conditions. To better understand the role of waterfalls as aquatic habitats in Costa Rica, macroinvertebrates were collected within the flow and spray zones of 38 waterfalls across the country, spanning an altitudinal range of 55 to 2,660 m above sea level, either by climbing up from the base or using rappel techniques from above. Additionally, in 11 of the waterfalls, corresponding river samples were taken to compare the associated assemblages. Caddisfly larvae were found at all waterfalls sampled, with a total of 10,642 individuals collected from 10 families and 24 identified genera. The family Hydroptilidae, with 12 genera, accounted for half of the individuals collected and was present in 37 of the 38 waterfalls. Metrichia (Hydroptilidae) and Calosopsyche (Hydropsychidae) were the most abundant genera, in terms of the highest number of individuals, and were most frequently collected, indicating a strong preference for this habitat. Larvae of Atanatolica (Leptoceridae) and Xiphocentronidae were quite common in spray zones. In contrast, Wormaldia (Philopotamidae), Contulma (Anomalopsychidae), Cerasmatrichia, and Alisotrichia (Hydroptilidae), although uncommon in rivers throughout the country, were also found abundantly in waterfalls, particularly the latter, which were especially abundant in intermittent and karstic waterfalls. Assemblages of Trichoptera in waterfalls were generally similar, with some differences associated with specific site characteristics, such as elevation or rock composition, and chemical factors like conductivity. This research constitutes the first systematic study of caddisfly larvae associated with waterfalls in the Neotropics. The results provide an important baseline for identifying new collection sites of adult caddisflies and for generating associations and descriptions of their larval stages, which may be unknown due to the understudied nature of this habitat. Key words: Aquatic insects, biodiversity, Central America, freshwater habitats, Neotropics Introduction Waterfalls are a unique habitat in freshwater ecosystems, characterized by physical characteristics distinct from those of other river habitats, as they lack a water column. Newson and Newson (2000) hydrologically classified this environment Academic editor: Blanca Ríos-Touma Received: 28 January 2025 Accepted: 14 June 2025 Published: 10 December 2025 ZooBank: https://zoobank. org/4F8C2E2F-4BFF-42AA-A4C7C0FF0DFDB28C Citation: Solano-Ulate D, Springer M (2025) Waterfalls as a reservoir for caddisfly larvae (Insecta, Trichoptera): exploring a poorly known habitat. In: Ríos-Touma B, Frandsen PB, Holzenthal RW, Houghton DC, Rázuri-Gonzales E, Pauls SU (Eds) Proceedings of the 18th International Symposium on Trichoptera. ZooKeys 1263: 479–498. https://doi. org/10.3897/zookeys.1263.148087 ZooKeys 1263: 479–498 (2025) DOI: 10.3897/zookeys.1263.148087 480 ZooKeys 1263: 479–498 (2025), DOI: 10.3897/zookeys.1263.148087 Darha Solano-Ulate & Monika Springer: Caddisfly larvae from Costa Rican waterfalls based on the flow type as a waterfall, describing it as having torrential water flow in the form of a free fall over the bedrock, at heights greater than one meter and usually covering the entire width of the channel. Additionally, waterfalls provide other microhabitats in hygropetric zones, such as laminar flow over different rock ‘roughnesses’ and spray zones, which usually have associated communities of bryophytes and algae (Zilihona and Nummelin 2001; Korsu 2004; Rackemann et al. 2012; Clayton and Pearson 2016). Although some of their implications for the ecology of certain organisms are known, they are little understood as a habitat in themselves (Rackemann et al. 2012; Baker et al. 2017). The diversity of aquatic macroinvertebrates associated with waterfalls has been little studied because they represent a habitat challenging to access and sample (Rackemann et al. 2012). Most research on macroinvertebrates in waterfalls has been conducted in the tropics of the Eastern Hemisphere. Some studies have recorded organisms associated with these environments (Yule 1996; Lee et al. 1993; Lee et al. 1998; Lee and Yang 2002; Sites and Vitheepradit 2007; Sites et al. 2011; Wijayanti et al. 2015), while others have evaluated ecological aspects, determining that waterfalls have assemblages distinct from those of the river itself (Palmer et al. 1991; Rackemann et al. 2012; Baker et al. 2016; Clayton and Pearson 2016; Baker et al. 2017). In the Neotropics, studies related to waterfalls have been scarce and mostly limited to specific records of organisms, although there is some knowledge about the preference of certain species for this habitat, specifically for Odonata (Calvert 1915), Hemiptera (Sites et al. 2013; Herrera 2016; Herrera et al. 2020), and the mollusk family Planorbidae (Vogler et al. 2019). Among the macroinvertebrates that have been recorded associated with waterfalls are the caddisflies (order Trichoptera) (e.g., Palmer et al. 1991; Yule 1996; Rackemann et al. 2012), whose larvae are especially suited to colonize these environments due to their ability to produce silk, which allows them to build shelters and attach themselves in the current (Mackay and Wiggins 1979; Wiggins 2004). The order Trichoptera is highly diverse in the Neotropics, occupying many niches in all freshwater ecosystems (Pes et al. 2018). Although adult diversity is relatively well understood in certain neotropical countries (e.g., Armitage et al. 2024), larval stages remain understudied and are unknown for most species, as well as several genera (Springer 2010; Pes et al. 2018). Despite their important scenic and recreational value for people, and even economic value as tourist attractions (Hudson 2013; Clayton and Pearson 2016; Ortega-Becerril et al. 2019), waterfalls, like freshwater environments in general, are threatened by multiple anthropogenic activities, as well as by climate change (Dudgeon et al. 2006; Rackemann et al. 2012; Sayer et al. 2025). Therefore, it is important to guarantee their conservation and to understand their contribution to regional biodiversity. This work aims to contribute to the knowledge of the caddisfly fauna inhabiting waterfalls in a neotropical country, highlighting the importance of these understudied environments as habitats for the local freshwater fauna. Materials and methods Study area This study was conducted in Costa Rica, located on the southern Central American isthmus and part of the Neotropical region. Due to its position between the Pacific 481 ZooKeys 1263: 479–498 (2025), DOI: 10.3897/zookeys.1263.148087 Darha Solano-Ulate & Monika Springer: Caddisfly larvae from Costa Rican waterfalls and Atlantic Oceans and its central mountain system, the country exhibits considerable topographic and climatic diversity within a relatively small area of 51,100 km2. These conditions result in high environmental heterogeneity and varying rainfall patterns, ranging from 600 mm in the Northern Pacific lowlands to more than 7,000 mm of annual average rainfall along the Caribbean slope and the southern Pacific area (Avalos 2019). Its hydrographic system is divided into 34 basins that drain through three watersheds: The San Juan River in the North, the Caribbean Sea, and the Pacific Ocean. Rivers and streams are abundant throughout the country, and due to the diverse topography, hundreds of waterfalls can be found at all elevations. Data collection A total of 38 waterfalls, with estimated heights ranging from 4 to 140 m, were sampled throughout the country, located between 55 and 2,660 m a.s.l. (Fig. 1; Table 1). Waterfalls were selected based on accessibility, their location mainly within well-preserved forested areas, and their representation of all three drainage areas (Northern, Pacific, and Caribbean slope) across the country’s altitudinal range. Thirty-four waterfalls have permanent flow, while four in the North Pacific dry forest region are intermittent (B2, B6, B7, and B8), becoming completely dry for several months, generally between January and late April. Two of the four intermittent waterfalls (B6 and B7) are karstic and share this characteristic with R27, one of the permanent waterfalls in the Southern Pacific lowland. Sampling took place between January 2022 and April 2023, and two collecting techniques were used: i) rappelling from the top of the waterfalls using appropriate equipment (Fig. 2A, B), Figure 1. Map of study sites. Geographical location of sampling sites in Costa Rica, according to their slope distribution. Refer to Table 1 for site details. 482 ZooKeys 1263: 479–498 (2025), DOI: 10.3897/zookeys.1263.148087 Darha Solano-Ulate & Monika Springer: Caddisfly larvae from Costa Rican waterfalls Table 1. Site information and physical and chemical data. Site codes of the 38 waterfalls sampled identified by sampling technique, intermittency, and karstic rock composition (B = Base, R = Rappel, i = intermittent, k = karstic), geographical coordinates, slope (P = Pacific, C = Caribbean, N = Northern), elevation and physical and chemical parameters measured in situ (h estim. = height estimated, T = temperature, DO = dissolved oxygen, Cond. = conductivity, ND = not determined). Site code Coordinates (DD) Slope Elevation (m a.s.l.) h estim. (m) T (°C) pH DO (mg/L) Cond. (µS/cm) B1 11.05756; ⎯85.58302 P 197 4 24.8 7.49 6.5 187.9 B2 i 10.56262; ⎯85.67559 P 55 6 26.9 8.34 7.1 374 B3 10.16276; ⎯85.60492 P 263 15 24.1 6.66 6.0 156.0 B4 9.99378; ⎯85.50336 P 234 10 ND ND ND ND B5 9.97609; ⎯85.62225 P 60 8 24.3 7.28 5.9 223 B6 ik 10.18462; ⎯85.36526 P 125 6 25.7 8.17 7.9 432 B7 ik 10.17434; ⎯85.37022 P 148 6 25.5 8.13 7.6 530 B8 i 10.29407; ⎯84.93556 P 360 10 24.7 7.94 6.9 165.3 R9 10.09342; ⎯84.51335 P 900 60 20.4 ND 8.3 98.5 R10 9.92698; ⎯84.44930 P 345 80 ND ND ND ND B11 10.07774; ⎯84.15257 P 1,445 5 17.7 7.04 8.3 73.8 R12 9.72049; ⎯84.26418 P 810 120 22.0 7.56 6.1 145.9 R13 9.90716; ⎯84.33932 P 430 25 ND ND ND ND R14 9.74341; ⎯84.58826 P 350 140 ND ND ND ND B15 9.60658; ⎯84.43174 P 85 10 26.0 8 6.9 174.4 B16 9.57920; ⎯84.21212 P 188 4 25.0 8 8.1 181.2 B17 9.47057; ⎯84.02183 P 450 5 25.5 7.5 7.8 114.8 B18 9.64511; ⎯83.85177 P 2,660 8 12.3 7.16 7.6 40.3 B19 9.69975; ⎯84.01320 P 1,900 10 16.4 4.8 8.2 55.1 B20 9.46822; ⎯83.72358 P 1,438 10 17.4 7.5 8.5 ND B21 9.18186; ⎯83.70674 P 150 4 27.0 8 7.7 ND R22 9.36995; ⎯83.48675 P 1,695 7 15.8 8.03 9.4 118.3 R23 9.37193; ⎯83.48308 P 1,820 50 16.0 8.07 8.8 118.8 R24 8.99363; ⎯83.32425 P 535 50 26.3 8 7.6 77.6 B25 8.97481; ⎯83.29524 P 96 10 25.8 8 6.7 407 B26 8.70710; ⎯83.17583 P 84 5 26.5 8 8.2 122.9 R27 k 8.71162; ⎯83.06985 P 190 25 ND ND ND ND R28 9.99041; ⎯83.70276 C 1,408 45 18.2 7.41 7.1 70.2 B29 9.86219; ⎯83.77659 C 970 7 ND ND ND ND B30 10.00475; ⎯83.61945 C 412 7 24.5 7.93 8.4 258 B31 10.11916; ⎯83.68175 C 627 7 18.5 7.95 8.4 45.6 B32 9.92423; ⎯83.18555 C 245 10 26.1 8.27 7.2 374 B33 9.65752; ⎯83.03632 C 215 60 25.7 8.41 7.7 110.9 R34 9.64289; ⎯82.87025 C 115 40 25.0 8.35 7.8 254 B35 10.20921; ⎯84.12853 N1,610 5 16.3 8.25 8.0 41.3 B36 10.21382; ⎯84.32641 N1,840 30 15.7 7.59 8.3 47.8 B37 10.20888; ⎯84.32899 N1,770 7 16.0 7.45 9.0 48.5 B38 10.37733; ⎯84.66341 N777 10 21.3 7.5 8.1 153 and ii) sampling directly from the base, climbing the waterfall wall when possible (Fig. 2C, D). All waterfalls were sampled once; eleven were sampled by rappelling, and 27 were sampled from the base. In all cases, sampling took place at least 1 m above the base to avoid contact with the riverbed microhabitats. For both collecting techniques, in each waterfall, the same microhabitats were qualitatively sampled, including both the direct flow and the spray areas. A hand net with a 250-µm mesh size was used to sample microhabitats with turbulent and/or laminar flow, while spray areas were sampled directly using forceps and an aspirator (Fig. 2E, F). Four physical and chemical parameters were measured 483 ZooKeys 1263: 479–498 (2025), DOI: 10.3897/zookeys.1263.148087 Darha Solano-Ulate & Monika Springer: Caddisfly larvae from Costa Rican waterfalls Figure 2. Collecting techniques and microhabitat sampling methods. Techniques used for collecting waterfall macroinvertebrates: A. Guided rappel; B. Rappel; C, D. Sampling from the base; E. Flow collecting with a hand net; F. Direct collecting with an entomological aspirator and forceps in spray areas. 484 ZooKeys 1263: 479–498 (2025), DOI: 10.3897/zookeys.1263.148087 Darha Solano-Ulate & Monika Springer: Caddisfly larvae from Costa Rican waterfalls in situ in 32 sites: temperature, pH, dissolved oxygen, and direct conductivity, using a PCE-PHD 1 multiparameter and Macherey-Nagel pH test strips (Table 1). Waterfall heights were estimated using the rope length in rappel sampling, and photographs with the collector present as scale for base-sampled waterfalls. Additionally, 11 waterfalls were selected of the 38 to compare caddisfly diversity and abundance between this habitat and the river caddisfly assemblages to identify any association or preference for this particular habitat. In these 11 rivers, macroinvertebrates were collected qualitatively either upstream or downstream, depending on access to the site, mainly in riffles using a D-net with a 500µm mesh size. All samples were preserved in the field in 95% ethanol and collected under R-SINAC-SE-DT-PI-003-2021 and R-SINAC-SE-DT-PI-007-2022 permits. Samples with collected organisms were sorted in the laboratory using a stereomicroscope and identified to the lowest taxonomic level possible (mainly genus), using specialized literature and local identification keys for Trichoptera larvae (Springer 2010; Pes et al. 2018). All specimens were deposited in the aquatic entomology collection of the Zoology Museum at the University of Costa Rica (MZUCR). Data analyses Since waterfall collecting was qualitative, Trichoptera abundance data were converted to relative abundances for all the statistical analyses. To compare Trichoptera diversity between waterfall and river habitats, relative abundances were analyzed using a Wilcoxon paired test for each taxon to determine the associations of taxa with each habitat. To examine the relationship between all the waterfall Trichoptera assemblages, a cluster analysis was performed using the Bray-Curtis similarity index. To explore the patterns of caddisfly diversity among sites, an unconstrained non-metric multidimensional scaling (NMDS) was conducted using the Bray-Curtis dissimilarity index. The environmental variables measured at the 32 sites (temperature, pH, dissolved oxygen, and conductivity) plus elevation were then correlated with their corresponding axis values using multiple linear regression. Significant environmental variables were incorporated as covariates in a second NMDS to improve the environmental explanation of the ordination pattern. Environmental data were previously transformed using Z scores. Analyses were performed using the software Past 5.2.1 (Hammer et al. 2001). Results Among the ten insect orders found in the 38 waterfalls, Trichoptera was the second most abundant group, after Diptera. It represented 33% of all collected macroinvertebrates, with 10,608 individuals from ten families and 24 identified genera (Table 2). Caddisfly larvae were present in all 38 waterfalls, with abundances of 9–948 individuals collected per site, while taxa richness ranged from 1 to 9 families, and 1–14 genera (Suppl. material 1). Hydroptilidae was the most frequently occurring caddisfly family in waterfalls, present in 37 of the 38 waterfalls sampled, with the exception of site B19 (Supp. material 1). Also, Hydroptilidae had the highest abundance with > 5,000 individuals, accounting for almost half of all caddisflies collected, as well as the highest taxonomic diversity with 12 identified genera (Table 2). Metrichia was the most frequently encountered genus in 33 waterfalls, with a little > 2,100 individuals. Its 485 ZooKeys 1263: 479–498 (2025), DOI: 10.3897/zookeys.1263.148087 Darha Solano-Ulate & Monika Springer: Caddisfly larvae from Costa Rican waterfalls Table 2. Taxonomic list of caddisflies in samples. Count of individuals (abundance) of caddisfly larvae collected per genus in the total waterfalls, waterfall subsample, their corresponding rivers samples, and quantity of waterfalls where each taxon was found (Freq.). Family Genus Total Abundance Freq. Waterfalls (n = 38) Waterfalls (n = 11) River (n = 11) Anomalopsychidae Contulma 92 48 3 8 Calamoceratidae Phylloicus – – 45 – Ecnomidae Austrotinodes – – 20 – Glossosomatidae Gen. Undet. 2 – 440 2 Helicopsychidae Helicopsyche 129 81 57 13 Hydrobiosidae Atopsyche 69 19 65 11 Hydropsychidae Calosopsyche 2,411 916 108 30 Leptonema 47 7 182 12 Smicridea 46 3 477 10 Gen. Undet. 14 12 – 2 Hydroptilidae Alisotrichia 2,214 1 1 16 Anchitrichia 1 – 7 1 Byrsopteryx 233 81 3 16 Cerasmatrichia 62 23 4 15 Hydroptila 2 1 24 2 Leucotrichia 112 96 39 19 Mayatrichia 3 3 4 1 Metrichia 2,106 509 125 33 Neotrichia 16 10 322 8 Ochrotrichia 66 64 1 5 Oxyethira – – 8 – Rhyacopsyche 133 39 22 18 Zumatrichia 74 74 3 10 Gen. Undet. 531 345 – 11 Lepidostomatidae Lepidostoma 57 2 198 2 Leptoceridae Atanatolica 629 321 14 15 Nectopsyche 3 1 279 3 Oecetis – – 38 – Triplectides – – 11 – Odontoceridae Marilia – – 36 – Philopotamidae Chimarra (Chimarra)4 4 181 1 Chimarra (Curgia)1,284 167 – 17 Wormaldia 127 13 – 8 Gen. Undet. – – 2 – Polycentropodidae Polycentropus – – 70 – Polyplectropus – – 3 – Xiphocentronidae Gen. Undet. 141 36 9 29 abundance was higher in waterfalls located at low and middle elevations. Also highly abundant was Alisotrichia, with > 2,150 individuals, although it was less widespread, as this hydroptilid was found in only 16 waterfalls, primarily located in lowland areas. The second most abundant and frequent family was Hydropsychidae, comprising > 2,500 individuals. Calosopsyche was the most frequently collected genus within this family, present at 30 waterfalls with 2,411 individuals (Table 2). Also abundant was Chimarra (Curgia) (Philopotamidae), with > 1,200 individuals collected from 17 waterfalls. However, it was only widespread on the Pacific slope, while a few organisms of Chimarra (Chimarra) were collected at a single site on the Caribbean slope (Suppl. material 1). Family Xiphocentronidae and genus Atanatolica (Leptoceridae) were commonly found in the spray areas of waterfalls, while the genera Atopsyche 486 ZooKeys 1263: 479–498 (2025), DOI: 10.3897/zookeys.1263.148087 Darha Solano-Ulate & Monika Springer: Caddisfly larvae from Costa Rican waterfalls (Hydrobiosidae) and Contulma (Anomalopsychidae) (Fig. 5F) were occasionally collected in a wide altitudinal range, and their highest abundances were obtained in intermediate to high elevations. On the other hand, the family Glossosomatidae and six additional genera were collected in fewer than three waterfalls, with Lepidostoma (Lepidostomatidae) and Hydroptila (Hydroptilidae) collected only in two sites, and Anchitrichia and Mayatrichia (Hydroptilidae) found in only one waterfall and with < 5 individuals each (Table 2; Suppl. material 1). At the 11 sites where both waterfall and river caddisfly assemblages were sampled, a higher taxonomic richness was observed in the rivers, comprising 14 families and 29 genera, which corresponded to 2,644 individuals (Table 2). Twenty-three taxa (21 genera and the families Glossosomatidae and Xiphocentronidae) were shared between the total waterfall samples and the river samples. The families Calamoceratidae, Ecnomidae, Odontoceridae, Polycentropodidae, and genus Oxyethira (Hydroptilidae) were only found in rivers, while the Philopotamidae genus Wormaldia and subgenus Chimarra (Curgia) were exclusively collected in waterfalls (Fig. 5B, C; Table 2), inhabiting the same type of shelters and habitus. Also, some of the less abundant taxa in waterfalls (i.e., Glossosomatidae; Chimarra (Chimarra); Smicridea) were very abundant in rivers, while others, like Anchitrichia and Mayatrichia, were rarely found in either habitat (Fig. 3; Table 2). Based on the Wilcoxon paired test, the genera Calosopsyche, Metrichia, Leucotrichia and Byrsopteryx were associated with waterfalls habitat, while Neotrichia, Leptonema, Smicridea, Nectopsyche, and subgenus Chimarra (Chimarra) were associated to river habitat (Fig. 3; Suppl. material 1). Helicopsyche abundances were similar between waterfalls and rivers; however, the case shapes observed in the waterfall specimens were very different, and they were found in spray areas (Figs 3, 5G). The cluster analysis revealed three main groups of waterfall Trichoptera assemblages (Fig. 4A). The first group consisted of sites B18 and B19, which were located at the highest elevations and shared the presence of the genera Atopsyche and Lepidostoma (Table 1; Suppl. material 1). The second group was formed by all the North Pacific intermittent and karstic sites (B2, B6, B7, and B8) and the karstic South Pacific site (R27), sharing approximately 65% assemblage similarity and the highest abundances of the genus Alisotrichia (Fig. 4A; Suppl. material 1). A third group was formed by all remaining sites, sharing different levels of similarity and slope locations (Fig. 4A). The physical and chemical measurements varied among sites, differing according to location. Temperatures varied between 12.3 °C for the higher elevation sites and 27 °C for the lowland waterfalls. Conductivity ranged from 40.3 to 530µS/cm, while pH values varied from 6.66 to 8.41, and one site exhibited a low pH of 4.8 (Table 1). Four of the five environmental variables analyzed with the multiple linear regression were significantly correlated with the sites ordination in the first NMDS conducted, elevation (R2 = 0.12, p = 0.04), temperature (R2 = 0.13, p = 0.04), pH (R2 = 0.23, p < 0.001) and conductivity (R2 = 0.28, p< 0.001). Sites ordination in the NMDS, including these covariates, reflected similar patterns as observed in the cluster analysis (Fig. 4B), differentiating the first group associated with high altitude and low pH values, the second group with high conductivity values, and showing no strong patterns in the ordination of the third sites group. The three genera mentioned earlier were also highly differentiated in the NMDS plot ordination between the first and second groups, as well as the third. 487 ZooKeys 1263: 479–498 (2025), DOI: 10.3897/zookeys.1263.148087 Darha Solano-Ulate & Monika Springer: Caddisfly larvae from Costa Rican waterfalls Discussion The overall composition of macroinvertebrate assemblages from Costa Rican waterfalls showed some similarities with those observed in studies of waterfalls in other regions, where the orders Diptera and Trichoptera were the most dominant taxa (Palmer et al. 1991; Yule 1996; Baker et al. 2016; Clayton and Pearson 2016; Dávila-Recinos et al. 2019). Dominance of families Hydroptilidae and Hydropsychidae observed in waterfalls in Costa Rica was similar to that observed in studies of waterfalls in other regions (Palmer et al. 1991; Yule 1996; Rackemann et al. 2012; Baker et al. 2016; Clayton and Pearson 2016; Dávila-Recinos et al. 2019). The groups identified in this study primarily correspond to highly rheophilic organisms, adapted to life in the current (Rackemann et al. 2012; Clayton and Pearson 2016), as is the case with caddisflies, due to their use of silk (Wiggins 2004). The diversity of caddisflies collected at waterfalls in the present study included ten of the 15 families recorded from Costa Rica (Springer 2010). Hydroptilidae presented the highest diversity and abundance, as well as the greatest frequency. Costa Rica has 17 reported genera of Hydroptilidae (Armitage et al. 2024), of which 12 were collected from the sampled waterfalls. Metrichia, the most frequent and abundant genus found in this study (Fig. 5D), is one of the most species-rich hydroptilid genera in the Neotropics, and its larvae are associated with fast currents and the presence of filamentous algae (Pes et al. 2018; Desidério et al. 2023). The waterfalls where Metrichia was most abundant were located at medium and low elevations, characterized by warm temperatures and high exposure to sunlight. Moreover, some were located in Figure 3. Relative abundances of Trichoptera in waterfalls versus river habitats. Comparison of the relative abundance of caddisfly larvae shared between 11 waterfalls and their corresponding rivers. Taxa abundance significantly different (p < 0.05) between habitats, as determined by the Wilcoxon test, is marked with an asterisk (*; refer to Suppl. material 1 for the Wilcoxon test results). 494 ZooKeys 1263: 479–498 (2025), DOI: 10.3897/zookeys.1263.148087 Darha Solano-Ulate & Monika Springer: Caddisfly larvae from Costa Rican waterfalls semblages and environmental factors, such as elevation or pH, underscore the importance of including additional sampling sites under the same conditions to better understand these distributional patterns. Although Trichoptera diversity could not be analyzed at the species level, the preference of some taxa for waterfalls, as shown in this study, highlights the importance of this habitat in maintaining the diversity of rheophilic insects and even hosting unique or rare species (Rackemann et al. 2012). These environments are also important in the face of fluctuations in river flow. With the decrease in flow due to climate change, waterfalls may be the only environment available for rheophilic macroinvertebrates, especially in regions with lower slopes along the basin (Rackemann et al. 2012). Conclusions This study provides a valuable contribution to our knowledge of Trichoptera diversity associated with waterfalls in a neotropical country. The presence of caddisfly larvae in all studied waterfalls, along with the high diversity reported, indicates that these constitute an important habitat for this diverse aquatic insect group. The high abundance of some genera in the waterfalls, compared to their much lower abundance or absence in the corresponding rivers, indicates a preference for these specific environments, possibly even representing their exclusive habitat. Additionally, some genera or species with similar niches may be adapted to inhabit these two habitats separately, thereby avoiding competition for resources. Waterfall caddisfly diversity was generally similar throughout the country, with differences mediated by site-specific characteristics such as elevation, the geological composition of the bedrock, and chemical factors like temperature and conductivity. The results obtained from this study underscore the importance of expanding research on larval taxonomy and ecology for a deeper understanding of the relationships between species and their habitats of development. This research, which constitutes the first systematic study of macroinvertebrates associated with waterfalls in the Neotropics, highlights the importance of exploring understudied environments to advance our knowledge of freshwater organism ecology and enhance conservation efforts for tropical biodiversity. Acknowledgments We thank Aldair Bejarano and Andrés Beita for their advice on data analyses, Paul Hanson for his English language corrections, and all the tourism projects, family, friends, and collaborators who contributed to this project in some way. Finally, we would like to express our gratitude to the two anonymous reviewers, whose detailed comments significantly improved the quality of this manuscript. Additional information Conflict of interest The authors have declared that no competing interests exist. Ethical statement No ethical statement was reported. 495 ZooKeys 1263: 479–498 (2025), DOI: 10.3897/zookeys.1263.148087 Darha Solano-Ulate & Monika Springer: Caddisfly larvae from Costa Rican waterfalls Use of AI No use of AI was reported. Funding We are grateful to the Vicerrectoria de Investigación of the University of Costa Rica for the financial support provided to this project, and to the Nature Experience Company for covering the registration costs to the 18th Symposium on Trichoptera for the first author. Author contributions Conceptualization: DSU, MS. Data curation: DSU. Formal analysis: DSU. Funding acquisition: MS, DSU. Investigation: DSU. Methodology: DSU. Project administration: DSU. Resources: DSU, MS. Supervision: MS. Writing – original draft: DSU. Writing – review and editing: DSU, MS. 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The Open Database License (ODbL) is a license agreement intended to allow users to freely share, modify, and use this Dataset while maintaining this same freedom for others, provided that the original source and author(s) are credited. Link: https://doi.org/10.3897/zookeys.1263.148087.suppl1