FAIRBANKS — All the big, black and yellow striped butterflies you see fluttering about are nothing unusual. It’s just the annual outbreak of hatching Canadian tiger swallowtails.
“Tiger swallowtails come out in the spring,” said lepidopterist Kenelm Philip, a senior research associate at the University of Alaska Fairbanks, who is better known as “the butterfly guy,” said. “You may see some still flying in July.”
While this year’s outbreak of Canadian tiger swallowtails is a noticeable one, it’s nothing extraordinary, Philip said.
“There have been similar outbreaks a number of times in the past here, leading to large aggregations at mud puddles along dirt roads and many seen flying along road margins in aspen forest areas (like Murphy Dome Road, or the Alaska Highway between Delta and Tok),” he wrote in an email.
In fact, there was a outbreak similar to this year’s in 2010. “The spots I was in last year there were similar outbreaks to this,” said Philip, who collects butterflies in the Bonanza Creek Experimental Forest just south of Fairbanks. “I remember people coming up to me to ask me what these large yellow butterflies were that they had never seen before in Fairbanks.
“It’s interesting how many people last summer said they’ve never seen these butterflies before and they’ve been here for hundreds of years,” he said.
There is a road named Monarch Road off Murphy Dome Road that was given that name a number of years ago by a local resident who told Philip that he saw numerous monarch butterflies feeding at damp earth on the road by his house. Philip checked and, sure enough, the monarchs were actually tiger swallowtails. Many people in Alaska and the Yukon call them monarchs, Philip said.
As their name implies, tiger swallowtails have distinctive yellow and black stripes on their wings and bodies. They are called swallowtails because they have long tails on their hindwings that look a bit like the long, pointed tails of swallows.
Their name is meaner than it sounds. The only thing tiger swallowtails eat is nectar from flowers, which is why they are often seen fluttering around blooming chokecherry trees at this time of year. They only live a month or two before laying their eggs. Tiger swallowtails overwinter in the larva or chrysalis stage, hatching in late May. Their primary predator, besides the windshields and grills of automobiles, are yellowjackets, which eat the butterflies when the butterflies are in caterpillar form, Philip said.
“The one year we had a really bad outbreak of yellowjackets in the 1990s, the following summer most of the species of butterflies of Alaska were down to about 2 percent of their normal levels,” he said. “They simply ate all the caterpillars.”
It was an amazing difference.
“The following summer they were a bit below normal and summer after that they were back to normal,” Philip said.
The average female butterfly lays about 200 eggs, so the populations can rebound quickly, he said.
Almost all Alaska insects have large, and apparently random, year-to-year fluctuations in their abundance, and the causative factors are not known, Philip said, adding that weather and predation “certainly” play a part.
“What I have seen here over the last 45 years is apparently uncoordinated fluctuations in the abundance of different species,” Philip wrote. “That would appear to indicate that the causes of these fluctuations are complex.”