What is that pinhead-sized cream bump on the underside of a milkweed leaf?

A monarch butterfly egg! Look for these ribbed eggs on the underside of the top tender leaves of milkweed plants. Keep watch for three to five days and you’ll notice the dark head of the developing caterpillar near the top of the egg. The caterpillar is about to emerge! 

A newly hatched monarch caterpillar, or larva, is shiny gray. Their egg shell is their first meal. Then they have the dangerous diet of sticky latex-filled milkweed leaves – about a third are mired in the milkweed latex. To avoid getting stuck in the glue, caterpillars cut a small circle in the leaf surface, blocking the flow of latex to the enclosed safe-eating area. 

After one to three days, they’ll shed their skin (become their 2nd instar) and don their characteristic black, yellow, and white bands. Over about a week or two, caterpillars shed their skin five times, grow to about two inches in length, and increase their body mass about 2,000 times! 

One thought on “Natural History Mystery

  1. what you are teaching is amazing. I wish ther was more of this for inner city kids, they know so little about nature.

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