Plecoptera, some publications mention the existence of a positive relationship between both (Khoo 1964; Elliott

It is commonly accepted in Plecoptera that the number of eggs a female may produce is directly propor-tional to its size (Khoo 1964; Brittain 1990; Peckarsky & Cowan 1991). In our research we have analyzed the relationship existing not only between the female size and the number of eggs, but also between its size and the egg size. Particularly we have focused on Isoperla nevada Aubert 1952. This species belongs to the super-family Perloidea, where the egg is little affected by differ-ences in the hydratation of the surrounding membrane (which avoids mistakes in egg measurements). Furthermore, eggs are completely mature in nymphs of last instars in this species (Tierno de Figueroa & Sánchez-Ortega 1999), so the female will not produce more eggs along its adult life