Every fall we receive calls from concerned individuals who have found a caterpillar late in the season, and are wondering what will become of it with the advent of the cold weather. Quite often the caterpillar in question is the Black Swallowtail (Papilio polyxenes), which is commonly found in vegetable gardens feeding on carrot, dill or parsley plants.
If you encounter one of these caterpillars in the fall, not to worry! You can leave the caterpillar to do it’s own thing. They are more than adept at dealing with the cold.
Butterflies are tougher than we give them credit for. They can fly 1000’s of kilometres to overwintering locations, lay hundreds of eggs within a matter of days, and they can do it all within a few short weeks of their adult lives. Plus, they can freeze solid, then thaw out and become alive again. Can you??
Insects are the original experts of cryopreservation (freezing for lengthened periods of time to wake up again in the future). With the good ol’ Canadian season of winter, these cold-blooded (or rather ecothermic) animals have had to come up with a way to survive the coldest part of our year. They contain natural antifreeze chemicals in their body which allow them to partially solidify (like controlled freezing), and then defrost in the spring to continue on with their life cycle.
Because insects like butterflies experience 4 distinct stages in their life cycle, that gives them 4 ways in which they can wait out the winter. Some butterflies hibernate as a caterpillar; very few hibernate as an adult butterfly; most overwinter in the chrysalis stage.
The Black Swallowtail is one such butterfly. See a photo below of the well-camouflaged chrysalis (pictured left) the caterpillar will form, often pupating in a horziontal position, suspended upside down from the plant stem. Not until the spring of next year will the adult adult butterfly emerge (pictured right).
So if you find a caterpillar in your garden – first, rejoice that you have habitat which obviously attracted a mother butterfly to lay eggs! Second, leave it outside – usually it’s best to let nature do it’s thing, and the caterpillar will find a place of its own to make a chrysalis. If desired, you can keep it in a container to wait & watch the butterfly emerge next year. But be careful to keep it in the cold! They’ll emerge too early if it’s in the warmth of your house, thinking it’s already spring.