 In 1917, he decided to leave Puerto Bertoni and together with his brother Guillermo Tell they travelled to Asunción where he began to work on his own scientific research, investigating the Paraguayan fauna, chiefly insects (Eumeninae, Polistinae, Masarinae, Sphecinae and Trigonalidae), as well as vertebrates, especially birds.He also made contributions in paleontology and archaeology.From 1930 to 1940, he was a professor of zoology, zootechnics, entomology, and plant pathology at the Escuela Superior de Agricultura and at the Escuela Nacional de Agricultura Mariscal Estigarribia.