Life history of benthic faunas of tropical high-altitude cold environments are poorly studied. Here, monthly larval and adult data are presented for Anomalocosmoecus illiesi at Saltana Stream in Ecuador. In cold conditions throughout the year (6 °C), this species showed an asynchronous and continuous production. Larval density showed two peaks in August and April. All five larval instars were present in most months. Using the size-frequency method an annual rate of secondary production per biomass of 4.8 was calculated. The measured biomass was 785 mg/m2.