What's That Bug? does not endorse extermination

Subject: Daniel – What’s This Egg?
Location: Hawthorne, CA
November 7, 2013 2:13 pm
Hi Daniel,
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

Moth Eggs, we believe

Moth Eggs, we believe

Hi Anna,
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.

Hi Daniel,
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.
Thank you,
Anna

Eggs

Eggs

Hi again Anna,
According to Backyard Nature and BugGuide, Mourning Cloak eggs are yellow and ribbed.  We don’t think your eggs are Mourning Cloak eggs.

Hi Daniel,
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.
Anna

Hatchling Caterpillars

Hatchling Caterpillars

Hi Anna,
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.
Anna

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.

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What's That Bug? does not endorse extermination
Location: Hawthorne, CA

2 Responses to Eggs on Milkweed might be Moth Eggs

  1. Kimberlie Sasan says:

    Not all moths lay eggs on the host plant. Some even lay eggs on brick walls or window screens, for example. Most likely these larvae ate their egg shells, had a bite of the plant they were on, and wiggled down a silk thread to find something more palatable.

  2. Nancy Macias says:

    I just found the same thing on my milkweed plant. I live in Southern California in Riverside County. I will leave them as long as they will not harm my Monarch caterpillars.

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