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I saw these caterpillars rapidly consuming a potato plant in Central Texas:

enter image description here

They have thin, dark green-blue bodies with yellow-white longitudinal stripes and a bright rust-red head. Their body seems to be covered in fine hairs which may be difficult to see in the photo. They are about 1 cm long.

On some leaves of the same plant I saw what appear to be eggs - little black balls 1-2 mm in diameter, with a shiny appearance reminiscent of black caviar (well, I suppose they are black caviar). They seem to cover only a handful of leaves, in groups of about 100 or so (rough guess). Some can be seen in the photo.

Curiously enough, nearby there were tomato and strawberry plants, but they were not affected, while the potato was extensively predated (a few dozen leaves consumed).

What are these caterpillars? How do you kill them?

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    $\begingroup$ The "eggs" are poop (good for th soil, though I wouldn't call them caviar ;). As the caterpillars grow, their poop increases in size. (I've raised a number of caterpillars in an effort to increase the population of endangered butterflies.) $\endgroup$ – anongoodnurse Mar 12 '17 at 19:27
  • $\begingroup$ I think they are eggs. They are round and occur in clusters (can't see easily in this picture). The caterpillars leave what I think is poop as well, it is smaller, cigar shaped, irregularly shaped and fluid. $\endgroup$ – Superbest Mar 12 '17 at 19:40
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    $\begingroup$ If they are in dense clusters, you are very likely correct. I don't know what you're describing is... I've never seen it. @theforestecologist will know, though. $\endgroup$ – anongoodnurse Mar 12 '17 at 19:43
  • $\begingroup$ @anongoodnurse They might be poop as well, it's hard to tell, but they seem like eggs to me (not in this photo). I'll see if I can get a high quality image of the eggs. $\endgroup$ – Superbest Mar 12 '17 at 19:45
  • $\begingroup$ A better photo would help! I'm stumped. I've searched everywhere I know to. I like the rear end of these caterpillars: slightly bulbous with kinda fake eyes? $\endgroup$ – anongoodnurse Mar 12 '17 at 19:47
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I believe this is the middle instar of a Southern Armyworm (Spodoptera eridania) larvae. Or some closely related species in the Spodoptera genus (family Noctuidae).

enter image description here

© 2016 Wings, Worms, & Wonder

The larvae undergo six instars as they grow to attain a length of about 35 mm.

Armyworms are so called because you typically find 100s at a time on a single leaf or plant. According to here:

Armyworms strike in the blink of an eye, and there are so many in their army that you will be finding them for weeks after the primary attack.

Behavior: larvae are mostly active at night and hide on leaf undersides, in curled leaves, or in leaf litter during the day.

  • This University of Florida site claims

    Young larvae feed on under surface of leaflets leaving upper epidermis intact ("windowpaned"). Older larvae consume foliage and eat large holes in fruit.

Range: native to the American tropics (occurs widely in Central and South America and the Caribbean). Also found in US (principally in the Southeast but extends West to Kansas and New Mexico). It also is reported from California.

  • Here's a map showing some confirmed sightings [source]:

    enter image description here

Host Plants: This species has a very broad host range including important crops (including potatoes).

  • I would be concerned for your nearby tomatoes, because thy too are a favorite food of these insects.

See here for more information including management suggestions.


Defecation vs. Eggs??

The picture in the question shows S. eridania's feces.

  • This Mississippi State site includes a great zoomed-in picture of S. eridania's feces:

    enter image description here

    © Lee Ruth

  • Note: caterpillars don't lay eggs. Only adult moths/butterflies lay eggs.

    Eggs: large masses of 100-200 eggs covered with moth body scales, found on underside of leaves, hatch in 3 days.

    enter image description here

    © 2016 Wings, Worms, & Wonder

    Here's a picture of inside the seed casing of closely related S. exigua [source]:

    http://www.soilcropandmore.info/crops/Insects/Insect-Pictures/Beet_Armyworm/VEG2.JPG

© 2016 Wings, Worms, & Wonder


Finally, here's a picture of the nocturnal adult:

enter image description here

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    $\begingroup$ Enter the cavalry! How did you find this? $\endgroup$ – anongoodnurse Mar 13 '17 at 0:21
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    $\begingroup$ haha :D. Well, truth be told, I don't know my lepidoptera as well as I could. So I simply started by googling a general description, then followed some links to seemingly related-looking species and eventually I narrowed it down. Took about 10 minutes :p. $\endgroup$ – theforestecologist Mar 13 '17 at 2:32
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    $\begingroup$ Really nice answer and info! $\endgroup$ – anongoodnurse Mar 13 '17 at 3:40

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