During two visits to Guatemala in 1974 and 1975 observations were made on the fauna inEichhomiagrowth of the small lake “Laguna Chichoj”;. Chemical and physical data and faunistic finds are reported. Particular attention was paid to the water miteArrenurus (Arrenurus) valenciusMARSHALL, 1919. Adults of this species occur commonly in theEichhorniagrowth. The larvae parasitize adultIschnura ramburi crédula(Zygoptera, Odonata). This fits the known pattern according to which nearly all species of the subgenusArrenurusare parasites of dragonflies belonging to both the Zygoptera as well as Anisoptera (Münchberg 1935, Mitchell 1959, Böttger 1965, Cassagne‐Méjean 1966, Cook 1974, Stechmann 1977). Also the first mentions in the literature on tropical species of the subgenusArrenuruspointed to Odonata as specific hosts (Münchberg 1958, 1959, 1960).