By Carrie Knutson, Horticulture agent

NDSU Extension – Grand Forks County

When I work in the garden, I keep my eyes open for any fun visitors I might find. Notable visitors have been garden spiders and centipedes, not my children's favorite. This year, I had my sights set on something they weren’t afraid to help me track down.

The visitor was a swallowtail butterfly. Two swallowtail butterflies had been visiting the flowers around my house. Even with my children scouting for me, I was never quick enough to get a picture. While I was working in a school garden, two swallowtail butterflies were there. They were more cooperative than the ones at home and patiently waited for their photograph to be taken.

There are different species of swallowtails, so I checked with Patrick Beauzay, NDSU Extension entomology research specialist. He narrowed it down to Eastern Tiger Swallowtail or a Canadian Tiger Swallowtail butterfly, leaning towards the first.

Eastern Tiger Swallowtails have a few characteristics that make them easier for most of us to identify. They are a larger butterfly with a wingspan of 3 to 5 inches. The adults are yellow in color and have four black bands on their front wings. The edges of the wings are black with a row of yellow spots.

Females will have blue on their hindwings. It is interesting to note that females are dimorphic. This means that females can have two color forms. In addition to the standard yellow, females can have a dark wing color.

Butterflies are in the scientific order “Lepidoptera.” Lepidoptera means “scale wing.” The scales, which are modified hairs, are responsible for the fantastic coloring we see in butterflies. Each scale is individually attached and can break off the wing. This can help the butterflies escape from predators.

Speaking of escaping from predators, the caterpillars of Eastern Tiger Swallowtail butterflies have three main defensive strategies to repel predators. Young caterpillars resemble bird droppings. Older caterpillars are green with two large eye spots. These are not true eyes, but another strategy to discourage predators. A final strategy the caterpillars use to discourage predators is a set of bright orange glands. The caterpillar has the ability to release the glands as needed. The glands will produce an offensive-smelling secretion that repels the predator.

The caterpillars can feed on a variety of woody plants like ash, birch and cherry. Adults feed on nectar from many different flowers.

Eastern Tiger Swallowtails can have two generations per year in our area. When the final generation caterpillars are mature, they will enter the pupal stage and overwinter on twigs or dead plant materials.

I hope to see more swallowtails in my gardens next year! Happy gardening!

NDSU Agriculture Communication – Sept. 4, 2025

Source: Carrie Knutson, 701-780-8229, carrie.knutson@ndsu.edu

Editor: Kelli Anderson, 701-231-6136, kelli.c.anderson@ndsu.edu