Butterfly Migration

Butterfly Migration

Like birds butterflies also migrate . But the reasons for the migration are not yet fully understood , since they usually do not survive to return to their place of origin to confirm to the definition of migration . The return journey is undertaken by the offspring only . This is essential since butterflies are short lived and usually cannot survive to complete the round trips . About 250 species in the world and 60 in India are reported to be migratory in nature . Migrating butterflies mostly belong to families , the Pieridae ,the Danaidae, the Nymphalidae and to a lesser extent, the Lycaenidae and the Hesperiidae . Such butterflies are found in the genera, Catopsilia, Euploea, Paranatica, Danaus, Papilio , Cynthia , Kallima and Lampides in India.
Butterfly migrations often take the form of persistent flight in one direction over long distance by large numbers of them and are clearly different from local flights around the breeding area , which are associated with feeding , mating and egg laying . Most migrations are usually characterised by the long periods which the butterflies spend in the air instead of resting or feeding on the ground. Flying for such long periods involves the use of enormous quantities of energy . This is provided from fat stored in the fat body , mainly in the abdomen . Butterflies are well endowed with fat body , mainly in the abdomen . Butterflies are well endowed with fat body when they emerge . After a long migration , the fat reserve may be reduced to 1-2 percent in the case of the Monarch butterfly . In females , the fat body is also used to nourish the developing eggs and this is partly why migrating butterflys often do not mature their eggs until after their long flight is completed . The total distance covered by a butterfly during its life time is known as life time track which may vary from 2 km in a few species to as high as 3200 km in the Monarch butterfly .

Butterflies mostly adapt a preferred compas direction for navigation . They undertake flinght during sunny periods only . The orientation is relative to the sun’s azimuth and persists at least for a period of overnight . As a result of this , butterflies travel slightly in different directions at different times of the day . Butterflies are not much influenced by wind directions in their travels . If following the winds , they may fly above the ground. On the days the wind is head-on or sideways , they may fly close to the ground . During favourable weather , the Monarch butterflies are seen soaring at height of 300 m above the ground .

Many theries have been postulated to explain the reason for butterfly migration. The most possible conclution is that butterflies undertake migration is response to unfavourable conditions such as lack of food , insufficient food of the right quality , over crowding or the onset of the winter. But butterfly migration is certainly brought about by environmental factors which set in anticipation of unfavourable conditions before they actually happen . These triggers acting through hormone system of the developing larvae , change the physiology of the next generation so that specifically migrant adults are produced .

Not much work has been done on butterfly migration in India recently . Our knowledge on this aspect is mainly derived from the works C. B . Williams , J. Evershed , H. D . Peile and W. H .Evans in the Palni hills , the Nigiris and the Himalayas . But thousands of butterflies comprising members of Danaus , Tirumala , Euploea , Catopsilia and Papilio migrate every year from the Sirumalai hills to the Kodai hills in Tamil Nadu during the month of October .

Elsewhere , the Monarch butterfly Danaus plexippus plexippus is known as the best migrant . It covers a distance of nearly 3200 km between its breading areas in Canada and northern United States , California and Mexico . There are reports that more than 14 million butterflies were found in areas of 1.5 ha in Mexico alone during migration . Their speed of light is usually 16 km / hour but can often attain a speed up to 48 km / hour . It has been found that a Monarch can fly about 960 km on the ‘tankful’ of nectar.

The most famous of the Monarch winter resort is Pacific Grove, California, where the butterflies have been returning year after year in large numbers for atleast a hundred years . During the month of October , the Monarch flutter in to the area where they form nightly clusters on trees and protected by City Ordinance No. 352 , which states that it shall be illegal to molest or interfere in any way the peaceful occupy of the Monarch butterflies on their annual visit to the city . There is a possible penalty of the dollar 5000 fine or a six- month jail sentence . Because Pacific Grove is an annual winter gathering place for the butterflies , it has become known as ‘’Butterfly Town , USA’’, and each autumn, the local children celebrate the return of the Monarchs with a parade .
Another famous migrant is the Painted Lady , Cynthia cardui . It is a cosmopolitan species , perhaps its food plants , the thistles , are also cosmopolitan . Migration of this butterfly occurs in both North America and Europe . Migratory movements have also been seen in Pakistan , South Africa and Australia . In Pakistan , a flight was seen moving southeast at 6000 m in August . This is probably the greatest elevation at which migrating butterflies have been observed .

Natural Enemies of Butterflies