diff --git a/src/modules/butterflies/butterflies_dispersal.c b/src/modules/butterflies/butterflies_dispersal.c
index 47b7c13a9cf1b87ef9da1a76744efd68dcfdbe61..cc373c5ccea2cdab3b0e8e1f0254af11ebd5298b 100644
--- a/src/modules/butterflies/butterflies_dispersal.c
+++ b/src/modules/butterflies/butterflies_dispersal.c
@@ -78,7 +78,7 @@ static void inline single_random_walk(struct cats_thread_info *ts, struct cats_g
                 // is the cell a valid dispersal target location?
                 if (!(data->info_layer[row][col] & BF_CELL_VALID_DISPERSAL_TARGET)) {
                         if (debug_rw) {
-                                fprintf(f, "%d,%d,%d,%d,%d,%d\n", row, col, steps + 1,
+                                fprintf(f, "%d,%d,%d,%d,%d,%d,%d\n", rw_num, row, col, steps + 1,
                                         module_conf->animal_dispersal_max_radius - steps - 1, 0, eggs_left);
                         }