Northern Butterflies

Though more-southerly states such as Colorado can claim 250 or more resident species of butterflies, at least 78 species flit around the Alaskan countryside.

Summer coolness rather than winter's cold limits the number of butterflies in the Arctic. Not having a source of heat within their bodies as mammals do, and yet needing a certain minimum body temperature in order to fly, butterflies must gain heat from their environment. In winter they are, of course, inactive but those who live over the winter in the adult stage avoid freezing damage to their body tissues by stocking up on self-manufactured antifreeze materials each fall. Some arctic butterflies survive, in larval stage, over two winters.

A few species of butterflies live only in the northern tundra. They can survive there in summer because they have become experts on making use of solar energy. By doing so, butterflies are capable of raising their body temperatures as much as 17°C (30°F) above ambient.

This information comes from Dr. Kenelm Philip who, though an astronomer by training, has pursued a hobby interest in butterflies until it has become his main avocation. In the process, he has become the leading expert on Alaskan butterflies. In his home near the University of Alaska at Fairbanks he has developed an extensive butterfly collection numbering in the thousands. He also has many fine photographs of butterflies showing all stages of their development from eggs, through usually 5 larval stages, into winged adults.

In describing the behavior of those species of butterflies living in the far north, Dr. Philip notes that one of the surprises is that at least one species is found mostly on south-facing rock slides. The reason is, he says, that the butterflies find these slides to be warmer than other areas. The rocks collect the sun's heat, and then the butterflies collect the heat from them, sometimes by laying their wings down against the hot rocks.

So that they can absorb more heat, northern butterflies tend to be darker than their low-latitude relatives. Females tend to be darker than males, probably because their reproductive task is more difficult, and, as Dr. Philip points out, reproduction is the only purpose in life of the adult butterfly.

Northern butterflies also are smaller than others because smallness is an advantage when it comes to absorbing heat from the surroundings. By contrast, mammals who are heat generators gain by being large.

Certain butterfly species are particularly clever about gathering up the sun's heat directly. When cold, they stand with wings folded and lean away from the direction of the sun so that they present the biggest area to the sun. When too warm, they lean into the sun to create minimum area. When disturbed, they also lean into the sun to minimize their shadows and thereby make themselves least visible to predators. One kind also soaks up heat by holding its wings at just the right angle to reflect the sun's rays directly onto the butterfly's central body.

Yet another interesting behavioral pattern of butterflies has been observed in the upland area of central Alaska. Collectors have found that certain species tend to cluster on hilltops, but that the vast majority found there are males. The mystery of why this occurs was solved when the collectors looked at the sex of butterflies flying up and down-slope below the hilltops. These butterflies were mostly females. Furthermore, it was found that the butterflies headed uphill were all virgins and those going down were impregnated. Thus, it seems that the butterflies are clever enough to use the local topography to increase the chances of getting together for reproduction.