Why do butterflies migrate? This is the first mystery. Some entomologists believe that the migration of insects is an instinctive behavior of species to escape from harsh environmental conditions. Related to genetic and environmental conditions. They put forward two hypotheses. The first hypothesis holds that migration is a direct response of insects to unfavorable environmental conditions at that time, such as lack of food, dry weather, overproduction and overcrowding. For example, when Pieris rapae emerges, if its parasitic plants cannot provide it with a better food source, it will migrate to find delicious food. On the contrary, if its parasitic plants can meet its needs, it will not move.
The second hypothesis holds that the change of some environmental conditions affects the individual development of insects and makes them develop into a migratory adult. These migrating adults are often obviously different from the resident adults in morphology, physiological state and behavior. They found that differences in photoperiod, temperature, population density and food conditions would cause obvious differentiation of adult physiology and flight ability.
However, neither of the above two hypotheses can explain the phenomenon of butterfly migration. For example, butterflies in America, before winter comes, they go to the Madre Mountain in Mexico for the winter in droves, starting from cold North America and Canada. The next spring, they flew to the north in droves, with a journey of 2880 kilometers. Every time the butterfly leaves, it covers the sky like a cloud. Someone has calculated the number of migrating butterflies, about 30 billion. Incredibly, they all have clear goals, fly directly to their destinations, never desert, and move between fixed locations regularly every year without making mistakes. Scientists still can't solve the mystery.
Why does a fragile little butterfly have great energy to fly across Qian Shan and sail 3000 ~ 4000 kilometers? Where does this energy come from? From a dynamic point of view, butterflies can't fly that far. This is the second mystery of butterfly migration.
Some scientists believe that butterflies can fly so far mainly because of the wind. They found that among many migrating insects, the migration direction is downwind, and the migration time is synchronized with the monsoon, that is, insects migrate from south to north and from east to west with the monsoon.
However, some entomologists believe that the above migration phenomenon is only the performance of wind-borne migratory insects. The migration direction and path of butterflies are not affected by monsoon. And they have a certain degree of self-control. They can fly against the wind or run against the wind to their destination.
Soviet scientists mikhailov and Svesenigov believe that the advanced and energy-saving "jet engine principle" is used in butterfly movement. They filmed the flight of the yellow butterfly with a high-speed camera, and were surprised to find that the wings of the butterfly stuck together for one third of the flight. They skillfully use the opening and closing of wings to make the front pair of wings form an air collector and the back pair of wings form a funnel-shaped air injection channel. Every time the butterfly flaps its wings, the size of the jet channel, the shape and length of the air inlet and air outlet, and the degree of contraction are all changing in an orderly manner. The air between the wings is squeezed out from front to back due to the constant flapping of the wings, forming a jet stream. Part of the energy of the jet is used to maintain the flying altitude, and the other part of the horizontal thrust generated by the jet is used to accelerate. Butterflies use this "jet engine principle" to cross the ocean. However, how butterflies manipulate this "jet channel" is still a mystery.
In the blue sky, how do butterflies navigate directionally, overcome all kinds of bad weather and rush to their destinations? This is the third mystery of butterfly migration.
Entomologist Baker specializes in insect navigation. He found that the Pieris rapae in western Europe always keeps a constant angle with the azimuth of the sun when it moves south in autumn. During the day, the azimuth of the sun changes with time, so does the migration direction of butterflies. Its daily migration path is a semi-circular arc from east to south and finally to west. During the whole migration season, a series of semicircular arcs are formed to migrate southward.
He also found that long-distance (more than 2000 kilometers) butterflies (such as butterflies) can adjust their course according to the daily change of the sun azimuth when navigating by the sun. In other words, its flight direction is not always constant with the azimuth of the sun, but changes with the azimuth of the sun. This change is regulated by the internal biological clock. For example, at 9 ~ 10 in the morning, if it flies towards the sun, at 3 ~ 4 in the afternoon, it will be adjusted to fly with its back to the sun, but it will always keep its flight path close to a straight line and reach its destination in the shortest voyage. His research seems to prove that butterflies navigate by the sun.
198 1, scientists from the University of Florida found tiny magnetic particles in the head and chest of butterflies. They believe that these micro-magnetic particles are the "navigator" of butterfly migration and the "biological compass" in the butterfly. However, it is a mystery how butterflies use micro-magnetic particles to find the geomagnetic field and determine their direction.