Salt Marsh Caterpillar Eating Hounds Tongue

2021 April 4

Sam and Rosie found me this woolly caterpillar on September 15, 2019.


They have gotten cautious about handling hairy caterpillars, because a lot of them have hairs that can get stuck in your skin like tiny, itchy little porcupine quills. So to avoid touching it, they brought back part of the plant it was eating, too. This gives us a nice 2-for-1 post today, with a caterpillar and its host plant.


So first, the caterpillar: From the woollyness, it is clearly one of the “woolly bear” caterpillars in the subfamily Arctiinae. After perusing the pictures, I think it looks like a Salt Marsh Caterpillar, Estigmene acrea. In particular, its face is an excellent match, with a yellow stripe running down the forehead, a yellow “moustache”, and the yellow prongs either side of the mouth.


I think the face coloration is probably more useful for ID than, say, the hair color in this case, because Bugguide says that their hair can range from jet-black to a pale blonde, although most common appears to be the black hair on the back with brown hairs on the side like we see in this one.

These caterpillars, like so many other woolly caterpillars, overwinter as nearly full-grown caterpillars, and then pupate in the spring. These particular ones then become large, white moths with black spots and orangeish-tan under their wings and on top of their abdomens.

Moving on to the plant it is eating, it has very distinctive seed heads, a cluster of four flat pads covered with velcro-like projections, surrounding a central spike.



The leaves are fairly long and stemless, broad at the base, and taper to a point.


The seed heads, which are very distinctive, look like “Hound’s Tongue”, Cynoglossum officinale. It took a while to identify it from the seeds, because it has actually fairly attractive reddish-purple flowers that draw most photographers.

So, unlike the caterpillar eating it (which is native to North America), Hound’s Tongue is an invasive from Europe that is rated as a “noxious weed” in several states and Canadian provinces. The plant itself is toxic to cattle, and in addition the seeds are one of the varieties commonly referred to as “stick-tights”. They actually are little pads coated with natural velcro hooks, and latch on to all varieties of cloth and animal fur with great tenacity. Animals therefore brush against them and spread them about willy-nilly.

Given that it is an invasive plant with substantial chemical defenses, it is good to see that at least one of our native insects appears to have developed a taste for it. Go, little woolly caterpillar, go!

One Response
  1. April 8, 2021

    The best part is that you have lab assistants that are on the lookout for wiggly data points!

    Great photos as always.

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