More About White-lined Sphinx Caterpillars

Some of you might be wondering why the white-lined sphinx moth caterpillars (Hyles lineata) are traveling in such numbers (see previous post). No one knows for sure what is going on. Two suggestions are that the caterpillars are looking for places where they can dig into the soil to pupate, and/or that they have run out of food and are looking for more. The caterpillars feed on common desert weeds, several wild relatives of four o’clocks. These plants are drying out since we haven’t had rain in a little while, so it is possible at least some of them are looking for food.

I was able to do a small experiment to test whether the pupation idea holds water. If you place one of these wandering larvae in a terrarium filled with soft, moist potting soil, you will be amazed at how fast they dig in. I expected to see a bit of wandering, then dig into the soil. Nope, almost as soon as their legs touched the soil they were digging. The hard clay desert soil (yes, our desert soil is clay rather than sand) is almost like cement where these larvae were found.

Update:  The white-lined sphinx moth emerged in September.


  1. Jill Plashko

    Our class is trying to raise the hummingbird moth caterpillar. We live in Wisconsin. I just found out that it needs soil, so I will bring some soil. What can we feed the caterpillar? He’s starting to not look very good. If he survives and turns into a moth, do we let him go or do we feed him? How do we take care of him? Thank you so much. Pleas right reply right away.

  2. Roberta


    Raising caterpillars can be an exciting project for the children, but not without its challenges.

    I would try the soil first, because if the caterpillar was out and about, it might have been looking for a place to pupate.

    About food, do you have any idea where the caterpillar was found? If it was on or near a plant, I would try giving it a few leaves of that plant. It might be kind of tricky to figure out otherwise without knowing exactly what kind of caterpillar it is. Can you give me a description?

    As for not looking good, it might be a couple of things. First of all, it could really be sick. Caterpillars do get diseases (fortunately not passed to humans). They also can be parasitized by tiny wasps or flies. Or, it could be that it is beginning to turn into a pupa. The caterpillar will start to swell and stiffen when it is getting ready to pupate.

    Good luck!

  3. Michael

    How large a tererium is required? My kids found one in the driveway here in Omaha, and want try raising it. I gave them a jar half-filled with moist soil, but “Cali” seems more intent on finding a way out than digging in.

    Its a fat black catapillar; head, tail, and horn all a matching tan color. I’m sure its a humming bird, and I assume it was feeding on elm, as there isn’t much else around here.

  4. Roberta

    The white-lined sphinx moth caterpillars can be black. Here’s a link to a photograph at What’s That Bug? Website:

    If the jar is too small, it might be an issue. It should be deep enough so the caterpillar can be covered with soil completely. Also, the texture and moisture level of the soil does matter sometimes. Finally, it might just not be done wandering yet. They go through a phase where they crawl about before digging in. If it was on a driveway, it is probably wandering.

    If it doesn’t dig in the next day or so, you might want to give it more soil or a different texture of soil.

    Good luck.

  5. Roberta

    If you are interested in caterpillars, check out this cecropia project:

  6. Cassi

    You say to use potting soil. Does it matter if the potting soil has fertilizer/plant food in it?

  7. Roberta

    I wouldn’t recommend potting soil with fertilizer in it.

  8. JoAnne

    How big do white-lined sphinx caterpillars get before they pupate? I have one trying to escape. It has soil but isn’t digging

  9. Roberta

    The size will vary, but if it has plenty of food and is starting to wander, it is probably ready.

  10. Amanda Stack

    How long does it take….going in the soil u til they emerge as a moth?

  11. Roberta

    Really depends on what kind of moth and what time of year. In the northern hemisphere right now it is headed for cooler temperatures, so many moths will go into their overwintering phase. That would mean they might stay underground for three or four months or possibly longer.

  12. Roberta

    However, it could be as short as two weeks.

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