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Predators and Parasites on the Prowl
By Elizabeth Howard

Female tachinid fly laying her eggs on the skin of a moth larva.
Photo by Robert W. Mitchell

Sucking the life from their victims, devouring the eggs, eating the young; you don't have to go to Africa to see it! You can explore the predator/prey interactions that monarchs face in your own backyard. You'll be amazed at what you see.

I certainly was! Right before my eyes, my monarch caterpillar suddenly split open--and out crawled 3 maggots. It was like science fiction....The white maggots, I learned later, were tachinid fly larvae.

The adult tachinid fly lays its eggs on monarch larvae--and the young flies develop inside. Just before my monarch caterpillar became a chrysalis, the fly larvae emerged from its body. I knew they were alive and was curious, so I kept them. Within a few days, the larvae developed into adult flies . . .

Not as nice as raising monarchs, maybe, but fascinating.

Try This!

  • Can you draw the life cycle of both monarch and tachinid fly? Read the text about the tachinid cycle above carefully, and draw from your knowledge about the monarch life cycle.

National Science Education Standards

  • Scientists use different kinds of investigations depending on the questions they are trying to answer. (K-4)
  • Plants and animals have life cycles that include being born, developing into adults, reproducing, and eventually dying. The details of this life cycle are different for different organisms. (K-4)

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