What are these black and yellow caterpillars all over Arizona?

TUCSON, Arizona (KGUN) – What are these black and yellow caterpillars all over Arizona? And why are there so many at the moment?

If you’ve been walking the river path or having a close look at the weeds that have been growing in your yard lately, you’ve undoubtedly spotted these scribbling creatures munching on weeds or scurrying over the asphalt. You’ll spot the white-lined sphinx caterpillars every year in Arizona and across North America, but a busy monsoon has given them quite a bit to chew on this year.

Gene room is an entomologist and Insect Collection Manager at the University of Arizona. He emailed some of our questions about these critters: why are they here, how long they will stay, and what effect they will have on our desert:

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What are these yellow and black caterpillars that we are seeing all over Arizona right now? Are they from our region?

These caterpillars, which come in a wide variety of body colors, are the immature stage of the white-lined sphinx moth (Hyles lineata). They are native to our region and widespread elsewhere, from Central America to Canada.

Are they dangerous?

No, they are harmless plant eaters, no need to fear or worry about them.

Do they have predators in our ecosystem?

Yes, other animals feed on caterpillars, they are a good source of protein. Native Americans also used them as a food source.

Why do they seemingly all appear at the same time?

It is not uncommon to see these caterpillars in large numbers, especially as they migrate from one food source to another. This is the time of year when we usually see the big migrations.

What is the reason for the large number of them this season?

While caterpillars are known to occur in large numbers during migration, their numbers could be even higher this year due to abundant food plants and other optimal conditions thanks to our monsoon rains. Over the past couple of years, we have experienced hot, dry summers with poor monsoons, which could explain the low numbers before this year, making this year’s large populations more visible.

When will they all start pupating? How long will they be there?

In our area, they typically have two broods each year, and their presence will begin to decline in late summer / early fall.

What type of butterfly / moth will they become?

It is a species of moth, the white-lined sphinx butterfly. Adult butterflies are important pollinators and can be seen flying at dusk and dawn. They are also known as hummingbirds because they fly from flower to flower in search of nectar, like hummingbirds. They also fly at night, so if there is an increase in numbers, they likely won’t be visible. The increase in the number of these moths is not of concern as they are harmless and important pollinators.

Andy Reago & Chrissy McClarren

What impact will they have on our ecosystem?

In the natural world, there is a good balance between plants and the insects that feed on them. Caterpillars act as natural “pruners” for plants, provide a food source for other animals that feed on them, and adult butterflies pollinate plants.

Any other info you would like to add?

If you have the chance, take the time to watch and observe these and other insects, learn something about their behavior, and appreciate the role they play in the natural balance of life in the desert. We are fortunate to live in a region with a rich diversity of flora and fauna.

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