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Very little is known about the biology of larval odonates from the Neotropical region, and in particular there are no data on behavioral changes during ontogeny and growth ratios, though both are crucial to understanding the dynamics of Odonata communities. Here we study growth ratio, development patterns and behavior of Rhionaeschna marchali larvae. We characterized larval instars using morphometric variables and describe their general behavior. Larvae were obtained from eggs laid by two females in the laboratory. They were maintained in individual containers until their emergence or death. Larvae hatched between 26 and 30 days after laying, and total development time was 340.5 (±5.9) days, with 15 instars. Growth ratios between successive instars averaged 1.12 for head width, 1.25 for head length, 1.20 for antenna length, 1.76 for forewing-pad length, 1.74 for hind wing-pad length, 1.19 for metafemur length and 1.22 for total length. Rhionaeschna marchali larvae spent most time “resting” and “grooming”. As size increased, larvae became more active and time “resting” decreased. The behavior “upwards abdomen bend” showed a decreasing trend with size, while “body bend downwards” became more common with increasing size. The high altitude (2600 m) of the region acts as a limiting factor for growth, and therefore this species completes one generation per year, similar to many temperate species. [ABSTRACT FROM AUTHOR]