Western Tiger Swallowtail


Common Name: Western Tiger Swallowtail
Scientific Name: Papilio rutulus
Order: Lepidoptera
Family: Papilionoidea - Swallowtail Butterflies
Subfamily: Papilioninae

Name
Swallowtails are named for the tails on their hindwings that resemble the long tail feathers of swallows. Papilio is from the Latin word papilio meaning "butterfly."

Range
Western North America, from eastern British Columbia to eastern North Dakota, south to northern Baja California and southern New Mexico. Rare stray to central Nebraska.

Description
Adult butterflies have a two-and-three-quarter to four-inch (seven- to ten-centimeter) wingspan. The wings are black and pale yellow with black tiger-stripes. The hindwings have tails at their lower tips that resemble the long tail feathers of a swallow; hence, their common name swallowtail. Also on the hindwing, there are narrow yellow spots along the wing's margin and orange tint on two spots near the end of the inner margin of the wing. Blue spots are found around the outer margin of the hindwing. The upper side of the hindwing may have a yellow spot on the outer margin. On the forewing, yellow spots form a continuous band along the outer margin of the wing. These yellow spots are bordered in black.

The adult antennae are knobbed but never hooked at the tip.

Life Cycle
A deep green, shiny, spherical egg is laid on the underside of a leaf. Eggs are laid singly, but there may be a number of them on the leaf. The caterpillars reach about two inches in length, are deep to light green in color, are swollen in the front, and have large yellow eyespots with black and blue pupils. There is a colored forked organ called the osmeterium located behind the head on the back of the caterpillar. This foul-smelling organ can turn inside out, and, along with the eyespots, may deter predators. The dark brown chrysalis overwinters slung from a twig or tree trunk. The chysalis is woodlike.
Swallowtail females may lay up to four batches of eggs in a season and up to one hundred eggs in total. The length of time that it takes for the larvae to emerge from the egg depends upon the weather, but generally, in summer, it takes four days. The larvae molt five times - called instars - before they pupate. After each molt, the caterpillar eats the old skin which is rich in nutrients.

Flight
February in southern California, May in Washington State. Normally in mountain areas adults fly from June through July. In the lower latitudes and altitudes there may be up to three broods, while in the more northern extents of the range there may be only one.

Habitat
Woodlands near streams and rivers, wooded residential areas, canyons, parks, and sagelands and mesas with creeks. May be seen at higher elevations.

Food
Caterpillars feed upon cottonwood, willow, quaking aspen, alder, maple, sycamore, hoptree, plum and ash. Adults feed on flower nectar from a wide variety of flowers.

Remarks
This is the commonest swallowtail observed in the West. A person can attract these butterflies to a garden by planting zinnias, milkweeds, thistles, penstemons and other flowers.

Certain species of wasps lay their eggs on a caterpillar as the caterpillar is spinning its last silk threads before it pupates. At this point the caterpillar is totally defenseless. The wasp's eggs will develop inside the caterpillar and feed upon it, killing the caterpillar.

In summer, it takes about ten to fifteen days (weather depending) for the caterpillar to change into the adult butterfly. The chrysalis will be green in summer and brown in winter.






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