The Migratory Butterflies

A favorite mystery of nature lovers is the behavior of the showy, black-and-orange Monarch butterflies, which appear to fly south in fall like migratory birds. Many authorities have doubted that insects have the brains and endurance to make a real migration to avoid the northern winter. The strategy of most insects is to sit out the winter as eggs or pupae. Last week Dr. Frederick Urquhart, director of Toronto's zoology museum, told about a 19-year study that tends to prove that Monarchs do migrate.

In 1938 Dr. Urquhart, then a young zoologist on the museum's staff, began trying to label Monarch butterflies to find out how far they fly. He soon ran into tagging trouble. A label that sticks firmly to a Monarch's wing is apt to make it aerodynamically unstable.

Insect Aerodynamics. During World War II, Dr. Urquhart worked for the Royal Canadian Air Force, and familiarity with airplanes gave him new ideas. He figured that small paper labels attached to the leading edges of the butterflies' wings close to the body instead of on the surfaces would not interfere as much with their flyability. Little by little Dr. Urquhart learned to make the labels stick by cutting small holes in the wing, folding the label over the hole and gluing the paper to itself rather than to the almost adhesive-proof wing. In 1950 and 1951 he tagged 3,000 butterflies, hopefully set them free, and waited for letters responding to the address tags. He got only one letter--from the meaningless distance of 40 miles.

But large-scale help was on the way. After Dr. Urquhart's wife wrote a nontechnical article in the American Museum of Natural History's magazine Natural History, eager volunteers came forward, and butterfly-tagging started on a continent-wide scale. Again, failure. It soon became apparent that the labels were not sticking in wet weather.

Matter of Taste. Next season Dr. Urquhart and his growing corps of volunteers were ready with waterproof paper labels. In 1955, 382 taggers put labels on 10,000 butterflies. This time 30 letters came. Tagged Monarchs had been found as far south as Virginia.

That winter Dr. Urquhart migrated south himself and found another reason why so few of his tagged butterflies were being reported. Ordinarily, birds do not eat Monarchs, and naturalists have assumed that they taste bad. Dr. Urquhart tried Monarchs and found that they have hardly any taste, resembling dry toast. So he was not surprised to find that birds eat labeled Monarchs without hesitation. The bit of white paper seems to spoil a natural color pattern that keeps birds away.

To overcome bird predation, Dr. Urquhart and his assistants tagged 20,000 Monarchs in 1956. So far, 125 have been found. Some butterflies tagged in Ontario got all the way to Texas and the Gulf Coast. Dr. Urquhart points out that several generations of Monarchs live and die each summer in northern regions, feeding principally on milkweed. Then the generation that is adult when cold weather approaches flies south to spend the winter. Since Monarchs do not breed in the south, the same butterflies move north again in spring.

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