Armyworm / Caterpillar Infestation

Hi What’s That Bug,

What are these? I found them on my wall between the window and the ceiling in Phoenix, AZ in March. They almost look like some sort of a black dust formation on the wall.

quickdrawtoo

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Hi quickdrawtoo,

You definitely made it hard for me to identify this one, and unfortunately, I can only give you a vague identification. Because they are so small, immature, and just hanging out on your ceiling, I really can’t give you much more than I think they look like newly hatched caterpillars or sawflies.

The fact that they are on your ceiling instead of a host plant is very intriguing. I have read about fall armyworm moths laying their eggs on the side of houses or under a flood light. This could be a similar situation.

Female fall armyworm moths like to oviposit or lay their eggs on light-colored surfaces. The caterpillars typically feed on corn, but they have over 80 plants they eat, including sorghum, Bermudagrass, and other grass weeds. They can also be detrimental to other field crops like alfalfa, clover, wheat, and rice.

My wife grew up on a cattle ranch and she remembers seeing acres of grass getting mowed down by an infestation of fall armyworms.

But, if they are getting into your house, the best thing to do is seal up any entrances, repair screens, and vacuum up any eggs or caterpillars you see. Other than that, I don’t think they would last very long in your house.

Dr. Bolton PhD

Author

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