A female Monarch deposits 300 to 500 eggs during her lifetime. We knew the rate of survival for Monarch eggs in nature was low, as low as 10 percent, but recently I learned it is actually closer to 5 percent.
Female Monarch curling her abdomen to deposit an egg.
Michigan State University phd entomology student Andrew Myers was determined to find out. He noticed much of the predation happened after nightfall. He camped out for three nights monitoring milkweed plants to discover who exactly were the culprits. The night time predators were earwigs, harvestmen, ants, tree crickets, and spiders. The daytime munchers included stinkbugs, plant bugs, mites, jumping spiders, and milkweed bugs.
Tip for raising Monarchs – When you see a female ovipositing eggs in the garden, wait until she has completely finished depositing her clutch and then head out immediately and snip the leaves and stems with the eggs. If you wait even an hour, many will have already been eaten.
We had a terrible problem with earwigs this summer. They ate every one of our Cecropia Moth eggs and newly emerged caterpillars, despite the fact that the tops of the glass terrariums are covered with several layers of cheesecloth and a fine mesh screen. The pesky creatures can slither into anywhere! Next year, all eggs and newborns are living in the house until they become too big to be an earwig or stinkbug meal!
Earwig and Stinkbug bug photos courtesy wikicommons media