Compléter Gap Fill Exercises 2Version en ligne ...... par Tea Cher 1 change butterflies decades Scientists monarch habitat US Mexico milkweed pesticides attention species miles But on the return trip to , an individual often makes the entire flight itself . That's a journey of up to 2 , 500 ( 4 , 000 km ) ! Today there are far fewer monarchs flying than there were in recent . Loss of their in Mexico is making it harder for the to survive . In many areas of the , farmers spray that kill plants . Climate is also affecting the timing of the butterflies' migration . hope that putting the monarch on the world's list of endangered will give this butterfly the , and help , it needs .