Since 1974, caddisfly researchers have convened every three years to share developments in all aspects of Trichoptera research, including faunistics, taxonomy, systematics, evolutionary biology, ecology, and biomonitoring. The 18^th International Symposium on Trichoptera took place in Quito, Ecuador, from 1 to 5 July 2024. It represented the first caddisfly symposium to be held in South America. Starting with the first meeting of Trichoptera workers initiated by the late Hans Malicky in Lunz am See, Austria, in 1974, the symposium has now been held on all continents except Africa. This special issue constitutes the proceedings from this international conference, highlighting novel insights into the study of the “underwater architects”.

The 18^th International Symposium on Trichoptera took place at the Universidad de Las Américas (UDLA), located in the Inter-Andean Valley, Quito (Fig. 1). The UDLA Park campus offered a perfect venue for our 18^th Symposium, including modern lecture halls, excellent nearby hotels, and easy access from an international airport. Fifty-four participants from 19 countries joined the symposium. The demographic makeup of the meeting was very evenly spaced, with numerous early-career researchers from Latin America attending the Trichoptera Symposium for the first time. At the same time, numerous long-standing regular attendees to previous symposia from North America, Europe, and Asia participated, including Professor John Morse, from Clemson University, who has attended all 18 symposia (Fig. 2).

Several institutions provided funding to sponsor the participation of students and young researchers for the Symposium. Applications for sponsorship were numerous, and we had a selection committee composed of Paul Frandsen, Ernesto Rázuri-Gonzales, Christian Villamarín, and Blanca Ríos-Touma. The recipients and the related sponsors were:

Diego Vimos, Universidad de Cuenca (Ecuador), and Cyntia Daniela Alvear, a young student from IKIAM (Universidad Regional Amazónia Ikiam), received support for registration and travel from the World Wildlife Fund. Nature Experience provided three student registrations for Dahra Solano, a student from Universidad de Costa Rica; Silvana Gallegos, from Universidad Nacional de Tucumán, Argentina; and Naomi Santana, from Universidad Tecnológica Indoamérica, Ecuador. Semblis Foundation, Netherlands, provided one registration, granted to Alejandra Correa-Bedoya from Universidad de Antioquia, Colombia.

The symposium program was organized by Blanca Ríos-Touma, Ralph W. Holzenthal, Jolanda Huisman, Paul B. Frandsen, Ernesto Rázuri-Gonzales, and Steffen U. Pauls. An opening reception welcomed all participants. The meeting was officially called to order by Blanca Ríos-Touma, the symposium’s organizer and convener. Prof. Gonzalo Mendieta, President of UDLA, gave the welcome remarks and wished the participants a successful meeting. His comments were followed by one of four plenary talks, each starting off the subsequent day’s sessions. These plenary presentations covered central topics in caddisfly research, including freshwater conservation, diversity and distribution, biogeography and faunistics, and systematics and taxonomy:

Each day included morning and afternoon sessions of contributed papers and a session devoted to posters. The contributed oral and poster presentations covered the fields of taxonomy, systematics, and evolution (15), diversity and faunistics (17), and ecology and biomonitoring (17). The symposium program, including abstracts of all presentations, has been digitally archived at https://doi.org/10.5281/zenodo.17665618. Also, a calming video of caddisflies in flight was prepared by Rogier Maaskant of Rotterdam, The Netherlands, and was displayed before each day’s presentations. A formal dinner was held in the old colonial part of Quito at the “Purísima” Restaurant on the last day of scientific presentations (Fig. 8). The symposium ended on 5 July with participants choosing between two one-day excursions to the Cotopaxi National Park or the Tandayapa Biological Reserve. This allowed participants to enjoy and marvel at Ecuador’s natural beauty and remarkable biodiversity (Figs 10, 11).

List of contributed oral presentations in alphabetical order of the first author (presenter in bold face; * denotes presentations published in the proceedings)

List of contributed poster presentations in alphabetical order of the first author (presenter in bold face; * denotes presentations published in the proceedings)

In the time between the 17^th International Symposium on Trichoptera in Lunz am See, Austria (5–9 September 2022) and the 18^th Symposium in Quito (1–5 July 2024) we lost several colleagues who will be greatly missed.

Fernando Muñoz-Quesada (1956–2024) was Professor at the University of Antioquia in Medellín, Colombia. A native of San José, Costa Rica, Fernando graduated from the University of Costa Rica where he worked in the ichthyology collection and at Costa Rica’s National Biodiversity Institute (INBio) on a project to survey the caddisflies of the country. He later attended the University of Minnesota where he revised the New World species of Wormaldia. He also described new species in several other genera from Costa Rica, including Leptonema, Austrotinodes, and Xiphocentron). After receiving his PhD in 2002, he spent the rest of his career at the University of Antioquia teaching and mentoring students in aquatic entomology. He was a caring and attentive teacher, loved by his students. He was known for his humor and his love of Latin American literature and culture. An obituary is planned by his students and colleagues at the University of Antioquia.

Carmen Zamora Muñoz (1964–2022) was a Professor of Zoology at the University of Granada in Spain. Born in Sevilla, she attended the same university at which she later spent her academic career. Her contributions to the taxonomy, biogeography, and ecology of Trichoptera of the Iberian Peninsula provided fundamental knowledge of evolutionary ecology and aquatic biodiversity of the region. Her 30-year career spanned research in Europe, North Africa, and the Americas. In addition to her dedication to teaching at the University of Granada, Carmen was recognized for her rigor, passion, and commitment to science, leaving an important legacy. An obituary by Núria Bonada, Javier Alba-Tercedor, and Marcos González is available in Limnetica (https://www.limnetica.com/documentos/limnetica/limnetica-42-1-i.pdf) as is one by Marcos González in Braueria (https://www.zobodat.at/pdf/BRA_50_0005-0010.pdf).

Dave Ruiter (1948–2021) was an expert on western North American caddisflies, with works that expanded to taxa distributed across the globe, including Japan. While Dave was perhaps best known for his work on Limnephilidae, including his 1995 treatment of the taxonomy of new world Limnephilus, his work encompassed many other groups of caddisflies. He had a particular interest in associating females to species and did so for many North American species. Dave is remembered by his colleagues as an enthusiastic researcher who was generous with his time in helping others. An obituary for Dave was written by his wife, Terri, and colleagues and is available in the Society for Freshwater Science news (https://freshwater-science.org/news/in-memorium-david-ernest-ruiter).

Sára Nógrádi (1942–2023) was an expert on the caddisfly fauna of Hungary and the Carpathian Basin. Her research focused on the faunistics of the region which culminated in 75 scientific publications and the fundamental book for the region “The Caddisflies of Hungary (Trichoptera)” which she wrote together with her husband Ákos Uherkovich. She was known for her detailed illustrations, many of which were published in the Caddisflies of Hungary. An obituary was written in Braueria in 2024 by Ákos Uherkovich (https://www.zobodat.at/pdf/BRA_51_0051-0052.pdf).

Hans Malicky (1935–2025) was an Emeritus Associate Professor of the University of Vienna and retired scientist of the Biological Station Lunz of the Austrian Academy of Sciences. Born in Theresienfeld and trained in Vienna, Hans was likely the most prolific caddisfly taxonomist of the last few decades, perhaps ever. With > 2500 new species described mainly from Europe, Asia, and Africa, he was well-known to the entire caddisfly community. He initiated the First International Symposium on Trichoptera, of which the Trichoptera Newsletter Braueria was an outcome. For 52 issues it served as both a publication outlet for faunistic and taxonomic studies, but also as an important repository for literature on caddisflies as well as information on caddisfly workers around the globe. While likely best known for his taxonomic work and his Atlas of European Trichoptera, Hans was also an excellent freshwater ecologist and biogeographer. He was also very generous in sharing his time and knowledge with colleagues from across the globe, many of whom visited him in his home in Lunz am See. An extensive obituary is currently in preparation.

David Allen (“Ets”) Etnier (1938–2023) was Professor Emeritus from the University of Tennessee, USA. He joined the faculty after completing his PhD at the University of Minnesota on the caddisflies of the state. He is best known for his discovery of the snail darter (Percina tanasi), a previously unknown species of fish in the path of a proposed federal dam project, thus testing the limits of the U.S. Endangered Species Act. Ets was an energetic instructor, researcher, and naturalist. His Regional Studies classes provided several generations of Tennessee biologists with active opportunities to learn about biogeography, bird songs, freshwater mussel taxonomy, and aquatic insect ecology, among other topics. His Trichoptera research included faunistic studies on the caddisflies of Minnesota and several southeastern US states as well as taxonomic studies on the genera Hydropsyche, Pycnopsyche, Agapetus, Neophylax, Rhyacophila, and several other genera. Prior to his death, he and his wife Elizabeth endowed the University of Tennessee with perpetual support for his fish and caddisfly collection, housed in the Department of Ecology and Evolutionary Biology.

Charles Rex (“Chuck”) Parker (1948–2023) was a biologist in Great Smoky Mountains National Park, USA. After his dissertation work at Virginia Polytechnical, where he examined the ecology of filter feeding caddisflies in some Virginia rivers, Chuck pursued postdoctoral work at the Royal Ontario Museum in Toronto. His employment in the park lasted 30 years under the umbrella of several different federal agencies. Chuck was a patient and keenly observant naturalist who added immense value to every project. He was instrumental in the historic All Taxa Biotic Inventory in the Great Smokies and partnered with specialists in many different insect taxa to leverage the ATBI effort to generate great scientific discoveries. He revised the world species of the odontocerid genus Psilotreta, the limnephilid genus Hesperophylax, the goerid genus Goerita, and the glossosomatid genus Agapetus in eastern N. America.

As with the conference, the ZooKeys Special Issue covers topics from evolution and phylogenetics to ecology, faunistics, and taxonomy of Trichoptera. In the individual papers, two themes are recurring: first, it is clear that we are still missing substantial basic knowledge about the diversity and distribution of caddisflies around the globe. This is true for adult and immature life stages, and even in regions with a long history of aquatic entomology research, e.g. Europe and North America. In the proceedings, five new species are described from North America. However, as can be expected, 22 new species are described from hyperdiverse and less intensively studied regions in Latin America. Evidently, we are still scratching at the surface of species and ecological diversity in caddisflies. Second, increasing the interdisciplinarity of the research being conducted is opening new avenues. For example, faunistics and taxonomy reveal many new species (even in putatively well-studied regions), are often conducted hand-in-hand, and increasingly focus on integrative methodologies.

The scope of the proceedings is wide-ranging with two, five, eight, and five contributions on the Trichoptera of Asia, Europe, Latin America, and North America, respectively. Two contributions address Trichoptera as a whole.