Thursday, July 26, 2018

Western Tiger Swallowtail Surprise

During a stopover at my parents' place after a trip to Okanogan County, we were sitting in the shade under an old lilac bush when a huge swallowtail floated by and started hovering around in the upper branches directly above us. I noted that in spite of its large size, it was a Western Tiger Swallowtail (Papilio rutulus) and not a Two-tailed Tiger (P. multicaudata) because the width of the black stripes were very wide. My parents frequently see swallowtails, sulphurs and other butterflies nectaring on the lilac when it is blooming, but it had long gone to seed at this point so we weren't quite sure what this swallowtail was doing because it was hovering from place to place like it was looking for nectar. I moved away from the lilac to get a better look at the swallowtail and observed it appearing to curve its abdomen toward a leaf while continuing to flutter its wings...suddenly the thought hit me, it was ovipositing! I was a little surprised to see it doing this on lilac, as they usually are found on cottonwood, aspen, willow or wild cherry, but I was so excited at the prospect of finally rearing a tiger swallowtail that I didn't think about it much and focused on solving the problem of reaching that high branch.

This particular lilac bush is more like a tree with its multiple 6+ inch diameter gnarly trunks and 20+ foot height. We estimate it is over 70 years old based on the age of the homestead and the knowledge that the lilac was already well-established when the old house was torn down to build the current house. The branch in question was about 14 feet high, but a regular ladder was out of the question because there would be nothing safe to lean it against. I couldn't back my pickup close enough without scratching it...what to do? Dad to the rescue! He fired up his dump truck and had it backed into the lilac in no time, let down the metal panels on the back so we could climb up in it, then set up a six foot step ladder in the bed, which was about four feet off the ground. I was then able to climb almost to the top of the ladder and pull the branch towards me. After a couple minutes of searching I located the leaf and found the egg!

Looking for the Western Tiger Swallowtail (Papilio rutulus) egg on our giant lilac bush. Photo courtesy of Mom, truck and ladder courtesy of Dad :)

Our unconventional setup
Success! Western Tiger Swallowtail (Papilio rutulus) egg on lilac

With egg in hand, I then started thinking that I didn't recall ever reading anything about Western Tigers using lilac as a larval host. A few book and internet searches later, and the only reference to lilac I could find was Art Shapiro's website citing lilac as a host in California. Willow (Salix), poplar/cottonwood/aspen (Populus), wild cherry (Prunus) and ash (Fraxinus) are listed as the hosts everywhere, with sycamore (Platanus), privet (Ligustrum) and sweet gum (Liquidambar) also listed by Art Shapiro. Interestingly, lilac (Syringa) is in the olive family: Oleaceae, which ash and privet both belong to. After talking to Washington lepidopterists, it seems my find is the first record of Western Tigers using lilac in Washington, possibly even anywhere outside of California (if you have recorded them on lilac anywhere, shoot me an email). It is likely that it has just been overlooked all this time, or perhaps they prefer old (i.e. tall) heirloom varieties over more recent varieties that might be less attractive to the butterfly. In any case, if you have lilac bushes, closely watch your tiger swallowtails to see if you notice any strange behaviors around them instead of simply nectaring on the flowers! Now is the time of year to look for tiger swallowtail larvae on all of the hosts listed above - watch for a caterpillar resting in the center of the top of a leaf. Early instars look like bird poop but become a camouflaged green with two large "snake eyes" as they mature. If you find any let me know!

My adorable little cutie-pie, barely a millimeter across with little teddy bear ears

Western Tiger Swallowtail (Papilio rutulus) larva at about 5mm long soon after hatching.
I am rearing it on lilac; a couple 3ft high suckers that Dad dug up from around the base of the old lilac which I then brought home and potted. So far the larva seems to be doing well and has been feeding for about a week now. I'll continue to post photos of it as it grows.


  1. I really liked this blog post of yours. I sent a link to a few folks I know who would be interested. Did you get any replies? Feel free to contact me via personal account.

  2. Did the larva develop normally on lilac and reach the pupal stage?

  3. No, the larva died a couple weeks later. I had trouble with mold on the leaves of the lilac sprout I brought home, so I'm not sure if that caused it or if it was just weak to begin with. I'll definitely be watching for more in the future!