Western Tiger Swallowtail Butterfly Inspection

A Western tiger swallowtail, also known as the Swallowtail butterfly, lives in North America. Its yellow and black wings make it easy to notice, and its high activity levels make it a pretty sight to observe.

Western tiger swallowtail species summary

Scientific NamePapilio rutulus
Family NamePapilionidae
Kingdom Animalia
Genus Papilio
HabitatAll sunny areas, riparian areas, riversides, hilltops
RangeWestern North America
Host PlantsMaples, cottonwood, willow, and wild cherry species
Butterfly DescriptionAngular wings with a yellow base and black stripes
Caterpillar DescriptionGreen, with a prominent black collar, becomes brown in the last instar

Butterfly Physical Description

Western Tiger Swallowtail Butterfly Feeding
Western Tiger Swallowtail Butterfly Feeding

The wingspan of a Western tiger swallowtail butterfly can reach 3 to 4 inches. Their hindwings are tapered towards the end and give them that distinct “tail” that is usually one of the distinguishing factors of Swallowtail butterflies.

When open, their wings are yellow, while blue and orange spots cover most parts of the medial part of their tails. The wings’ appearance is similar on the ventral side, except that the rounded edges of the hindwings have cyan-blue markings parallel to the edges. 

Black stripes and markings outline their triangular forewings and hindwings. The markings on these large butterflies then vertically and perpendicularly cross the wing surfaces.

The difference between Eastern and Western Tiger Swallowtail

The Western tiger swallowtail is slightly less yellow and has fewer blue patterns on the hindwings. The lines that outline their wings are also more black. On the other hand, the Eastern tiger swallowtail has more blue coloration (female) or is almost completely black (male) on its hindwings and is brightly yellow.

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What color is the Western Tiger Swallowtail caterpillar?

The larvae typically look like bird droppings when they hatch from their eggs. They molt at least 5 times, and their shade brightens up a bit every time.

They will turn a bright green hue once they finish the fifth molting process. At this point, their eyespots are large and yellow with blue and black pupils.

Western tiger swallowtail caterpillar
Western tiger swallowtail caterpillar

A fully-grown caterpillar can be as long as 2 inches. Once it reaches this stage, it will hang itself upside down and turn into a pupa.

The pupa appears dark brown during the winter and green during the summer season, with black spines and golden spots on their ventral sides. To predators, the chrysalis will look like an inconspicuous piece of wood.

Where do Western Tiger Swallowtails lay their eggs?

Some of the host plants where Western tiger swallowtail butterflies lay eggs include:

  • Quaking Aspen (Populus tremuloides)
  • Gray Alder (Alnus incana)
  • Western Sycamore (Platanus racemosa)
  • Scouler’s Willow (Salix scouleriana)
  • Cottonwood (Populus sect. Aigeiros)
  • Catalina Cherry (Prunus iliucifolia ssp. lyonii)
  • Bitter Cherry (Prunus emarginata)
  • Green Alder (Alnus viridus)
  • Sandbar Willow (Salix exigua)

Where do Western tiger swallowtails live?

In general, Western tiger swallowtail butterflies love the warmth and thus favor sunny areas, so they frequent riversides, hilltops, meadows, and roadsides. Here are some other types of habitats where their broods thrive:

  • Rural woodland edges
  • Urban gardens and parks
  • Riparian areas
  • Tundra-edge deciduous woods
  • Wooded suburbs
  • Alpine terrains (above treelines)
  • Canyons and canyon streams 
  • Coastal parts of an area
  • Streamsides

What do Western tiger swallowtails eat?

This adult butterfly species love to get nectar from the following native plants:

  • California Buckeye
  • Alders
  • Aspens 
  • Maples
  • Zinnia
  • Poplars
  • Thistles
  • Yerba Santa

Behavior and life cycle

Instars feed on the leaves of the host plants as soon as they emerge from the eggs. They spin rounded patterns of silken pads on the leaves, which serve as their resting spots when they are not feeding.

Unlike other species that hang themselves upside down on leaves when ready to pupate, they form their chrysalis on the ground in leaf litter. They also do this when they overwinter.

Female Western tiger swallowtail butterflies lay about 100 eggs that appear deep green, spherical, and shiny. They usually do this on the underside of the leaves.

As for the males, they typically swarm together with other Swallowtail species on rivers, streams, and sometimes pools. They suck in water from puddles and muddles to extract moisture and minerals they need for future reproduction.

Despite this behavior, they are considered a loner type of species. During the breeding season, the males go around the habitats mentioned above in search of females. 

Common Predators

These are the Western tiger swallowtail butterflies’ natural predators:

  • Flycatchers
  • Owls
  • Woodpeckers
  • Praying mantis
  • Hornets
  • Blackbirds
  • Robber flies
  • Spiders
  • Squirrels
  • Possums
  • Dragonflies
  • Raccoons
  • Hawks

Do Western Tiger Swallowtails live in the Eastern United States?

The Western tiger swallowtail butterfly lives in Western North America. They live in California, New Mexico (the US), and the southern regions of British Columbia (Canada). This species is similar to the Eastern tiger swallowtail, which lives in the Eastern US, so people who live in the Eastern US may think it’s the Western.

Are these butterflies rare?

If you’re on the constant lookout for these butterflies, you’re in luck because they are not as rare as you may think. Their prevalence in different countries suggests that they are a common species.

Are there any cultural customs and beliefs related to this butterfly?

Some groups believe that these butterflies represent your inner self. Therefore, when a Western tiger swallowtail lands on you, it may mean that you’re receiving a blessing in the form of transformation, good life, endurance, positive change, and hope for the near future.

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