Aug. 14, 2009
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| Western Tiger Swallowtail, image taken in east Davis in August 2009. Click to enlarge. (Photo by Greg Kareofelas) |
DAVIS—It’s almost as if he has a “tiger by the tail.”
In this case, it’s the Western Tiger Swallowtail butterfly (Papilio rutulus), back in the Davis area after a 15-year hiatus.
Butterfly expert Arthur Shapiro, professor of evolution and ecology at the University of California, Davis, says the Western Tiger, one of the largest and showiest of butterflies, “was relatively common in Davis until the early 1990s, when it suddenly disappeared.”
“Since then there have been no sightings at all, or at most one or two per year--until this year. Now it looks like it's back as if nothing had happened!”
The butterfly, with a wingspan of three to four inches, has bright yellow wings edged with a black border. Four diagonal stripes grace the top of the wings, and blue and orange spots on the hind wings, near its tail. Its normal range covers much of western North America, from British Columbia to North Dakota in the north to Baja California and New Mexico in the south. It nectars from many flowers including thistles, abelia, California buckeye, zinnia, and yerba santa.
Shapiro has tallied about 100 sightings in the Davis/Vacaville area since March 26.“It’s still flying today.”
Florian Altermatt, a visitor from Switzerland, spotted the first Western Tiger March 26 near the Memorial Union, UC Davis campus. He had no idea the species had "disappeared.”
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| Art Shapiro (Photo by Kathy Keatley Garvey) |
Shapiro saw the next one on April 12. Between then and June 4, six more sightings occurred: on campus, in central Davis, and in both east and west Davis.
“The second generation was first spotted on campus on June 24 and in the next five days there were eight more sightings--on campus and in central Davis,” Shapiro said. “There's no doubt the Western Tiger is breeding here again. The mystery is why it ever went
away."
Davis naturalist and photographer Greg Kareofelas reports seeing the Western Tiger in his yard in east Davis “consistently” since the last week in June. “It’s an incredible phenomenon,” he said. “I have lived in Davis since 1972 and this is the most I have ever seen. In the last 18 years of ‘Davis record keeping,’ I’ve been averaging about one Davis sighting a year. This year, I have been seeing about one a day for the last seven weeks. My data is only for my yard in east Davis. So this year is unparalleled.”
Lynn Kimsey, director of the Bohart Museum of Entomology, and professor and vice chair of the UC Davis Department of Entomology, said the Bohart Museum “has a large collection of these butterflies, in part due to the efforts of Art Shapiro and his students. The collection is important because it archives where the swallowtails have been found in the past, and changes in their distribution over time.”
“I haven’t actually seen them in town,” Kimsey said. “I guess it’s because I’m always looking for insects on the ground.”
The Western Tiger Swallowtail, Shapiro said, “occurs in riverbank forest in our part
of California, where its caterpillars feed on the leaves of several deciduous trees including sycamore (Platanus), ash (Fraxinus), cherry (Prunus--in our area non-native), and willow (Salix).”
These trees are widely grown in cities throughout California, he said. “The butterfly is a regular breeder in old, established residential neighborhoods where it is often seen sailing majestically up and down the streets 25 feet off the ground, or taking nectar from butterfly bush (Buddleia) in gardens.”
It is common in Capitol Park and the “Fabulous Forties” in Sacramento, in the East Bay and even in San Francisco, where it breeds on plane trees (Platanus) at Civic Center Plaza.
And Vacaville? “They are just as common in Vacaville as they are here in Davis this year,” he said. “In Vacaville, they never went away.”
“I set a site-specific day record for me with 22 at Gates Canyon (Vacaville) on July 7, and another with eight in the Suisun Marsh on Aug. 9,” Shapiro said.
The professor said the Western Tiger Swallowtail can be seen in Vacaville in season on Buck Avenue as well as in Alamo-Buck Park at the west end of Buck Avenue.
“The Papilio rutulus boom extends at least from Suisun to midtown Sacramento, but seemingly no further east. In fact, this year there have been no rutulus seen at Castle Peak--which is not all that odd.”
So why did it disappear from leafy, green Davis?
Shapiro said it's just one of many Lepidoptera to vanish with no obvious explanation: for example, the Davis fauna of late winter-early spring moths, quite prevalent in the 1970s and early 1980s, has disappeared. Most of these were tree-feeders, too.
Shapiro is happy it’s back. He asks that sightings be sent to him at amshapiro@ucdavis.edu for documentation purposes.
Shapiro maintains a Web site at http://butterfly.ucdavis.edu/, covering more than three decades of collected data. He authored the 359-page Field Guide to Butterflies of the San Francisco Bay and Sacramento Valley Regions, published by the University of California Press. Tim Manolis provided the illustrations.
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--Kathy Keatley Garvey
Communications specialist
UC Davis Department of Entomology
(530) 754-6894
