Since 1974 caddisfly researchers have met every three years to share developments on all aspects of Trichoptera research from faunistics, taxonomy, systematics, evolutionary biology, ecology and biomonitoring. The 18th International Symposium on Trichoptera took place in Quito, Ecuador in July 2024, and represents the first caddisfly symposium to be held in South America. This special issue represents the proceedings book from this international conference, but also welcomes other contributions that unveil novel insights into the "underwater architects"