Friday, September 21, 2012


Learned today that Black Swallowtails do not migrate to warmer climes as the Monarchs do. They over-winter as chrysalides instead—and much more rarely as caterpillars.

The butterfly in chrysalis stage can evidently detects the season from a combination of the temperature and the length of the daylight; it then knows what is coming and begins to prepare. In that process it generates a kind of anti-freeze; the chemical protects it for the duration. If it is still a caterpillar, one source informs me, it will burrow a deep hole and, within that, wrap itself into a leaf. I think we witnessed such a case late last fall when a fairly large caterpillar simply disappeared; but we knew too little. Its feeding plants were then in a large pot full of earth, and it may have buried itself. That pot went outdoors for the winter.

Two quite cold nights—with our furnace coming on—sent me on this investigation. We have two candidates for over-wintering. Brigitte has named them Castor and Pollux (although they might well be Castoria and Polluxina). They formed their chrysalides on September 14 and 16 respectively. We shall see. For starters, I took their container out into the cold this morning lest they be deceived.

1 comment:

  1. That is interesting. Glad you're letting the Castor and Pollux feel the temperatures.


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