Subject: Daniel – What’s This Egg?
Location: Hawthorne, CA
November 7, 2013 2:13 pm
When I was out looking for Monarch Caterpillars on the Mexican Milkweed the other day, I spied these eggs on the bottom of a leaf. Can you please identify what laid them? I’m hoping something beneficial.
Signature: Thanks, Anna Carreon
We just discovered this unanswered request that dates to our return after a short holiday. The shape of the eggs and the quantity leads us to believe these are Moth Eggs. Biophotonics has a photo of Milkweed Tiger Moth Caterpillars, Euchaetes egle, that is attributed to Kailen Mooney of the University of California, Irvine, however, to the best of our knowledge, the Milkweed Tiger Moth is an eastern species. See the BugGuide range map for confirmation. We have not had any luck locating any moths that feed on Milkweed in California.
I think these may have been Mourning Cloak eggs. They all hatched out at once, ate their egg sacs, and left. I thought it very strange that they would be on milkweed and noted that these caterpillars sometimes feed on rose leaves. There are rosebushes on either side of the milkweed plant in question, but I never spied any activity there. I guess it will remain a mystery.
I still think these are Mourning Cloak eggs, but have been known to be wrong on more than one occasion. This picture was taken the day before they hatched and, now that I think back, they did not eat the egg sacs. Here’s a photo of them just after hatching.
It might be very difficult to identify these Caterpillars from a photo, but they still look like hatchling Tiger Moth Caterpillars to us. Mourning Cloak Caterpillars will stay together as they grow. Too bad you lost track of them. We may never know for certain.
Now I see that you are most likely correct. I am confused, though because you say the Tiger Moth is an Eastern species. I’ll try to do some research into this. These caterpillars definitely did not stay together. They disappeared, never to be seen again.
Hi again Anna,
Tiger Moths are a subfamily Arctiinae, not a single species. See Bugguide. There are many western species, but the Milkweed Tiger Moth (see BugGuide) is an eastern species. We have numerous western species. Perhaps it was a Painted Tiger Moth. The Painted Tiger Moth is a general feeder, but we don’t think it would feed on milkweed. Female Painted Tiger Moths often lay eggs on buildings, but the caterpillars will not eat the buildings. Upon hatching, the caterpillars soon disperse and begin feeding on a wide variety of plants in yards.
P.S. We will be away for a week. This entire correspondence is postdated to go live on January 20. We will return to the office late next week.