EVERETT — An abundance of yellow butterflies has made it a colorful summer in the Pacific Northwest. It’s not just casual gardeners who have noticed the boom in tiger swallowtails.

As butterfly caterpillars eat and grow, they go through stages (called “instars”), shedding their skin and often changing their appearance somewhat as they pass from one stage to the next.

The yellow butterfly vine is best propagated from cuttings and can grow 10 to 20 feet tall and wide as shown here in bloom at Victoria Educational Gardens at Victoria Regional Airport. Small ...