Week 10: Butterfly ID Quiz

We’re back to caterpillars this week with some closely related species:

Which of these caterpillars is a Canadian tiger swallowtail?

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The caterpillar on the right is the Canadian tiger swallowtail.
The caterpillar on the left is a spicebush swallowtail.

The spicebush swallowtail has four dots - two large false eyes and two extra dots behind them. The Canadian tiger swallowtail has two smaller false eyes on its enlarged head with two bands - yellow and black behind them. These large false eyes are used for defense to make their head appear to be that of a larger animal, like a snake. Both caterpillars are green when they are younger and change color near pupation. The spicebush will turn yellow like a dying leaf and then brown, while the Canadian will turn the greenish-brown color seen above.

What about the horns?
These are a defensive organ called the osmeterium found in all swallowtail larvae. When the larvae are threatened they flash the osmeterium and emit a foul odor. This combined with the eye spots make this organ look like a tongue - contributing to their predator-scaring snake disguise.

Spicebush Swallowtail by Lynn Harper (iNaturalist)

Canadian Tiger Swallowtail by Kent McFarland (iNaturalist)

This week get ready to test your knowledge of skippers here!