A fly screen with lateral winding for doors or windows comprising: - a lower guide and an upper guide - a plurality of lower tracks and a plurality of upper tracks which are designed to be positioned respectively in the lower guide and in the upper guide in a closed configuration of the fly screen, - a slider which is slidable along the lower guide and the upper guide , - a lateral box comprising a winding tube , and - a mesh comprising a lower end and an upper end respectively slidable in the lower and upper guides, wherein the mesh is fixed with a first lateral end to the slider and with a second lateral end to the winding tube of the lateral box , wherein the lower guide and the upper guide define a plane (S) for sliding of the mesh , and wherein each lower track defines a sliding channel of the mesh delimited by a first lateral surface and a second lateral surface opposite to each other, each lateral surface comprising a plurality of brushes protruding towards the inside of the sliding channel, the brushes being arranged inclined towards a lower surface of the sliding channel and configured for locking the lower end of the mesh in the case in which the lower end tends to escape from the sliding plane (S) , wherein the upper guide defines a sliding channel delimited by a first lateral surface and a second lateral surface opposite one another, each lateral surface of the upper guide comprising a plurality of first brushes , inclined towards an upper surface of the sliding channel of the upper guide , the first brushes being configured to support the plurality of upper tracks , characterized in that each lateral surface of the upper guide comprises a plurality of second brushes located below the first brushes and protruding towards the inside of the sliding channel of the upper guide , the second brushes being arranged inclined towards an upper surface of the sliding channel of the upper guide and configured for locking the upper end of the mesh in the case in which the upper end tends to escape from the sliding plane (S). - a lower guide and an upper guide - a plurality of lower tracks and a plurality of upper tracks which are designed to be positioned respectively in the lower guide and in the upper guide in a closed configuration of the fly screen, - a slider which is slidable along the lower guide and the upper guide , - a lateral box comprising a winding tube , and - a mesh comprising a lower end and an upper end respectively slidable in the lower and upper guides, wherein the mesh is fixed with a first lateral end to the slider and with a second lateral end to the winding tube of the lateral box , each lower track defines a sliding channel of the mesh delimited by a first lateral surface and a second lateral surface opposite to each other, each lateral surface comprising a plurality of brushes protruding towards the inside of the sliding channel, the brushes being arranged inclined towards a lower surface of the sliding channel and configured for locking the lower end of the mesh in the case in which the lower end tends to escape from the sliding plane (S) , wherein the upper guide defines a sliding channel delimited by a first lateral surface and a second lateral surface opposite one another, each lateral surface of the upper guide comprising a plurality of first brushes , inclined towards an upper surface of the sliding channel of the upper guide , the first brushes being configured to support the plurality of upper tracks , characterized in that each lateral surface of the upper guide comprises a plurality of second brushes located below the first brushes and protruding towards the inside of the sliding channel of the upper guide , the second brushes being arranged inclined towards an upper surface of the sliding channel of the upper guide and configured for locking the upper end of the mesh in the case in which the upper end tends to escape from the sliding plane (S). <EOS>