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Tuesday, July 15, 2014

Western Tiger Swallowtail (Papilio rutulus)

Western tiger Swallowtail (Papilio rutulus) nectaring on Purple Sage (Salvia leucophylla)

Nothing is more enchanting than the appearance of large butterflies in our gardens. July is typically a busy butterfly month, but we’ve been watching the Western Tiger Swallowtails since spring.  If you live in the western United States you may be enjoying them as well.   To learn more about attracting butterflies to your garden see our June 2012 posting (http://mother-natures-backyard.blogspot.com/2012/06/butterfly-gardens.html ).

The Western Tiger Swallowtail ranges through much of western North America from N. Dakota south to New Mexico; west from British Columbia, Canada to Baja California, Mexico. The species is similar to the Eastern Tiger Swallowtail (Papilio glaucus) of eastern N. America and is found mostly between sea level and 5000 ft. (1500 m.).  The tiger swallowtails were formerly included in the genus Pterourus. 

Many westerners recognize this butterfly on sight - it’s large, distinctively colored and relative common. While actually at home in riparian woodlands and stream sides, it’s not unusual to see these butterflies in gardens and city parks.  One thing is certain: you’re more likely to see them in places that have food for their larva (caterpillars): Willows, Cottonwoods, California Sycamore (Platanus racemosa) and ash (Fraxinus spp.).  That’s why we have so many Tiger Swallowtails in Mother Nature’s Backyard.

Two other swallowtail species visit western Los Angeles county gardens (see above).  The Giant Swallowtail is a large black butterfly with a prominent yellow triangle on its open wings.  The Anise Swallowtail, common in some neighborhoods,  looks like a large yellow butterfly wearing a set of heavy black shoulder-pads with 3 short yellow stripes.  The Pale Swallowtail, which has similar markings to the western tiger swallowtail, is black and white (rather than black and yellow) and is rare in gardens.

Western Tiger Swallowtails are large butterflies.  Their wingspan can be as much as 2 ¾ to 4 inches (7 to 10 cm), making them one of the largest butterflies in many western gardens. Females are larger than males, but otherwise similar in appearance.  They are brightly colored, predominantly yellow and black, with spots of blue and red/orange.  The wings are striped like a tiger – four black stripes on yellow - on both the upper and under surface.  The margins of both fore- and hind wings are edged in black with yellow dashes.
Western Tiger Swallowtail (Papilio rutulus)
The hind-wings have ‘tails’ reminiscent of the tail of a swallow – hence the common name ‘Swallowtail’. The lower inner margins of the hind-wings have a dot of blue and orange (some individuals may have additional blue spots, particularly on the underside of wings). The head and body (thorax and abdomen) are striped yellow and black. The antennae are knobbed (not hooked) at the tip. You can get a good look/photo of these butterflies as they sun or nectar, often with their wings spread.      More excellent photos are available  at: http://www.butterfliesandmoths.org/species/Papilio-rutulus and http://nathistoc.bio.uci.edu/lepidopt/papilio/tiger.htm .
While limited to summer in colder climates,  Tiger Swallowtails fly from January through September/October (even all year) in warm S. California sites.  You may note that spring-flying individuals are slightly smaller and paler than their summer counterparts.  But they still are distinctively Tiger Swallowtails.
It’s not uncommon to see males patrolling back and forth through the garden, searching for receptive females.  In the wild, males congregate at shallow pools or damp ground to drink and obtain dissolved minerals. This behavior (termed ‘puddling’) is not often observed in gardens, in large part due to a lack of suitable damp ground.  Males also feed on carrion and dung.  And both male and female adults visit a wide range of flowers to obtain nectar (food). 
Females lay eggs on the leaves of host plants (plants that provide larval food).  The eggs, which are shiny, round and deep green, are laid singly on the undersides of leaves. A female produces approximately 100 eggs in her lifetime.   If you are fortunate, you may witness a female laying eggs.  She curves her abdomen down, releases a sticky egg and deposits it on the leaf. The tiny caterpillar (larva) emerges 4-5 days later.  Ah, the miracle of life!
Tiger Swallowtail larvae go through five life stages (instars) before they pupate (form a chrysalis or cocoon).  They molt between each stage, growing an entirely new exoskeleton to fit the growing, changing caterpillar.  During the early stages, when the larvae are small, they look like a bird dropping – a deterrent to birds and others that might want to eat them.  For pictures of Western Tiger Swallowtail larvae see: http://butterfliesofamerica.com/papilio_rutulus_immatures.htm and http://www.wildutah.us/html/butterflies_moths/papilionidae/h_b_papilio_rutulus_immatures.html
Later stage instars are bright green with a pair of large eyespots, resembling eyes, at the tail end.   This protective coloring also serves to camouflage and fool  predators.  The larvae also possess another potent weapon.  They can raise a brightly colored (and foul smelling) forked organ called the osmeterium (‘stink horn’) from behind the head. The sight and smell of a raised osmeterium are enough to frighten off many potential predators.  
Tiger Swallowtail larvae eat leaves, grow and poop – that’s what caterpillars do!  The larval food plants vary somewhat from place to place but always include willows (Salix species), Cottonwoods and Aspen (Populus species) and Ash (Fraxinus species).  In California, additional native plant sources include the California Sycamore (Platanus racemosa), plants in the Cherry Family (Prunus species), Birches (Betula species) and Alders (Alnus species).  The larvae usually live high in trees and shrubs and are seldom seen by humans.
Western Tiger Swallowtails have 2-3 broods in warm coastal S. California (only one in colder areas).  Summer larvae progress through their development rapidly – sometimes as quickly as 15-20 days from egg to butterfly. Summer broods tend to be the largest.  Late (fall) broods over-winter in the chrysalis in many areas.  As an aid to camouflage, the summer chrysalids are bright green while the fall/winter ones are brown to blend in with surrounding wood.   Butterflies emerge from the winter chrysalids from January through spring, depending on the ambient temperature.
Western Tiger Swallowtail (Papilio rutulus) sunning on Lemonadeberry (Rhus integrifolia)
Watching butterflies in the garden is a fascinating hobby.  It’s inexpensive, you don’t have to travel and you can learn a great deal about the natural world. You may even discover something new about insect behavior!  All you really need are patience and a comfortable place to sit; a camera and binoculars are also useful tools. 
Here are some simple things you can do to make a home for Western Tiger Swallowtails

  1. Plant their favored plants. 

Adult (nectar) plants (relatively simple to provide)

·        California native plants: California buckeye (Aesculus californica); native dogbanes (Apocynum species); native Milkweeds (Asclepias fascicularis; A. eriocarpa; A. speciosa); native Milkvetches (Astragalus species); Cobwebby thistle (Cirsium occidentale); Yerba Santa (Eriodictyon spp.);    Dunn’s Lobelia (Lobelia dunnii  var. serrata); perennial Mints (Monardella lanceolata ; M. linoides; M. macrantha; M.  villosa); Penstemons; Salvias (especially Purple Sage, Salvia leucophylla, in our garden); Wooly blue-curls (Trichostema lanatum)

·        Other garden plants:   abelia, agastache, butterfly bush (Buddleia), lilac, lillies, mints, zinnia

Larval (host) plants (require a little planning)

·       California native plants: cottonwoods, poplars and willows are too big and invasive for most yards.  Try instead native White alder (Alnus rhombifolia), native Prunus species like Hollyleaf & Catalina Island cherries (Prunus ilicifolia), Desert Peach (Prunus andersonii), Desert Almond (Prunus fasciculata), Desert Apricot (Prunus fremontii), native plums and Western chokecherry (Prunus virginiana var. demissa) and California ash (Fraxinus dipetala).

·        Other garden plants: anything in Prunus family (cherries; plums; peaches; nectarines; apricots)

  1. Use pesticides sparingly – or not at all.  Practicing Integrated Pest Management (IPM) is a safer, greener approach to managing garden pests.  Keep plants healthy, use simple preventive measures and use chemical pesticides only as a last resort.   To protect pollinators, never apply pesticides to blooming plants.  For more see: http://www.xerces.org/pesticides/ 
  2. Provide a source of water.  This doesn’t need to be large or sophisticated.  We use glazed clay saucers (like you put under pots) filled with garden soil, gravel and water.  You’ll need to add water daily in warm weather.  If you’re clever, you could probably adapt a hose-fed birdbath dripper to provide water during the day.
  3. Provide sunny, safe places for sunning.  Butterflies need warm, safe places to perch and warm themselves.  Tiger Swallowtails prefer to perch on leaves -  most shrubs with medium to large leaves are fine.  The area should be sunny and out of wind if possible.
  4. Encourage your neighbors to follow butterfly-friendly practices in their yards. 
    Western Tiger Swallowtail (Papilio rutulus) nectaring on Purple Sage (Salvia leucophylla)
We encourage your comments below.   If you have questions about Western Tiger Swallowtail or other gardening topics you can e-mail us at :  mothernaturesbackyard10@gmail.com


  1. I live in Cheyenne, WY and have been seeing this butterfly every day, several times a day. Last year I had 25+ monarch caterpillars and watch and video/pictures of them going into and coming out of crysalis. Now that I have read this, and know what to look for, I hope to find swallowtail caterpillars

  2. I live in Northern IL right on boarder of WI. I was backing out of my driveway and saw this brown caterpillar crawling across the driveway, so stopped and put it on a giant hydrangea we have by our front door. Should I move it or will it find its way to the trees it seeks out?

    1. They can crawl amazing distances. Will probably make it to where it needs to go.

  3. Albuquerque, NM Thank you for the information... each year we have a single butterfly float through our yard several times a day in late spring, summer. Would love to have more! Perhaps this info will help...

  4. First time for me to see this butterfly in eastern San Diego County. It was visiting our plumbago hedge. Beautiful and large!

  5. First time for me to see this butterfly in my yards here in eastern San Diego County, CA. It was visiting our plumbago plumes along with the regular Monarchs. Large and striking!