Insect Identification on milkweed

Asked August 26, 2018, 12:14 AM EDT

What are these insects on the showy milkweed plant. Are they native? Thanks

Multnomah County Oregon

2 Responses

The newly hatched insects on your milkweed appear to be caterpillars. It's very difficult to identify such young caterpillars but it's very likely they're leaf eaters.

If you are in the experimental mood you could try to rear some until they develop considerably further. This brochure tells how to rear monarch butterflies, but the process is the same for other caterpillars. In your case, the food will also be milkweed because that's where you found them. (

You might keep 6 or so in a large jar and feed them milkweed leaves. To make certain they stay in their temporary housing, add a vented lid such as a piece of fabric (or sturdy paper toweling) secured with a rubber band.

Or you could take the easier route and leave them on the plant as they develop further.

That said, I located a source which discusses milkweed tussock moths. (See But as near as I can discover, their range is Maine and southern Canada to Florida; west to Minnesota and Texas. So, not a good match.

I will contact an entomologist for help with this identification.

While you wait for the next email, here's an image of the various developmental stages of milkweed tussock caterpillars to compare with what's on your milkweed:

I apologize, but I can’t add anything definitive, beyond what Jean has already written. It is surely a caterpillar - but too young to ID with any degree of confidence. Since insects in milkweed are fairly limited, i’m Drawn to milkweed tussock moth or monarch butterfly. But Multnomah County seems too far north for monarchs, and the egg mass doesn’t look right (monarch eggs are not usually laid in a mass, but are instead laid singly). The Tussock moth range is too far west, but the egg mass looks correct. I would be interested to see a photo of the caterpillars at a later stage, is that is att possible - perhaps in a week? Keep in mind that in a week’s time, yellowjackets might capture and kill the caterpillars, or something else might carry them away. But, if at all possible to have a look at older instars, I would love to have a second crack at an ID.