BACKYARD SECRET—ZEBRA SWALLOWTAIL CATERPILLARS ARE CANNIBALS

     One of the most striking butterflies that flutters about our yards is the black and white striped zebra swallowtail.  One of the reasons that it is far less common than the eastern tiger swallowtail is probably linked to the fact that it has only one larval host plant—the pawpaw.  On the other hand, the tiger swallowtail uses a variety of plants as hosts for its caterpillars.

     Faced with often scarce larval food plants, one of the ways that zebra swallowtail maximizes the numbers of caterpillars that reach adulthood is its caterpillars sometimes act as cannibals.  Let me explain.

     Female zebra swallowtails typically lay a single egg on the underside of a pawpaw leaf. However, at times they will lay two or more eggs on the same leaf.  When this happens and the eggs hatch one of the young caterpillars will often devour its rival. This cannibalistic behavior ensures it will not have to share precious food with a rival.

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