Citizen science is a research approach that involves collaboration between professional scientists and non-professional volunteers. The utilisation of recent online citizen-science platforms (e.g. social networking services) has greatly revolutionised the accessibility of biodiversity data by providing opportunities for connecting professional and citizen scientists worldwide. Meteorus stellatus Fujie, Shimizu & Maeto, 2021 (Hymenoptera, Braconidae, Euphorinae) has been recorded from the Oriental Islands of Japan and known to be a gregarious endoparasitoid of two macro-sized sphingid moths of Macroglossum, Ma. passalus (Drury) and Ma. pyrrhosticta Butler. It constructs characteristic star-shaped communal cocoons, suspended by a long cable. Although M. stellatus has been reported only from the Oriental Islands of Japan, the authors recognise its occurrence and ecological data from Taiwan and the Palaearctic Island of Japan through posts on online citizen-science groups about Taiwanese Insects on Facebook and an article on a Japanese citizen-scientist's website. Through collaboration between professional and citizen scientists via social media (Facebook groups) and websites, the following new biodiversity and ecological data associated with M. stellatus are provided: Meteorus stellatus is recorded for the first time from Taiwan and the Palaearctic Region (Yakushima Is., Japan). Cechetra minor (Butler, 1875), Hippotion celerio (Linnaeus, 1758) and Macroglossum sitiene (Walker, 1856) (Lepidoptera, Sphingidae) are recorded for the first time as hosts of M. stellatus and two of which (C. minor and H. celerio) represent the first genus-level host records for M. stellatus. Mesochorus sp. (Hymenoptera, Ichneumonidae), indeterminate species of Pteromalidae and Trichogrammatidae (Hymenoptera), are recognised as hyperparasitoid wasps of M. stellatus. Parapolybia varia (Fabricius, 1787) (Hymenoptera, Vespidae) is reported as a predator of pendulous communal cocoons of M. stellatus. Meteorus stellatus is recorded for the first time from Taiwan and the Palaearctic Region (Yakushima Is., Japan). Cechetra minor (Butler, 1875), Hippotion celerio (Linnaeus, 1758) and Macroglossum sitiene (Walker, 1856) (Lepidoptera, Sphingidae) are recorded for the first time as hosts of M. stellatus and two of which (C. minor and H. celerio) represent the first genus-level host records for M. stellatus. Mesochorus sp. (Hymenoptera, Ichneumonidae), indeterminate species of Pteromalidae and Trichogrammatidae (Hymenoptera), are recognised as hyperparasitoid wasps of M. stellatus. Parapolybia varia (Fabricius, 1787) (Hymenoptera, Vespidae) is reported as a predator of pendulous communal cocoons of M. stellatus. The nature of suspended large-sized communal cocoons of M. stellatus and the importance and limitations of digital occurrence data and online citizen science are briefly discussed.