Walnut Sphinx Moth: All You Need to Know

The Walnut Sphinx Moth is an insect primarily found in North America. It plays a role in the ecosystem, particularly in deciduous woodlands where it is native.

Understanding its characteristics and behavior is essential for both entomologists and those interested in the natural world.

In this article, we will discuss this beautiful moth.

Walnut Sphinx Moth

Historical Background

The Walnut Sphinx Moth was first described in 1797 by an English botanist named James Edward Smith

Later, in 1809, German entomologist Jacob Hübner established the genus Amorpha, with the Walnut Sphinx Moth being its sole species.

Scientific Classification

  • Family: Sphingidae
  • Genus: Amorpha
  • Scientific Name: Amorpha juglandis

This classification places the Walnut Sphinx Moth within the Sphingidae family, commonly referred to as the hawk moths

Physical Description

The Walnut Sphinx Moth’s physical attributes vary across its life stages, from the greenish caterpillar with white bumps to the brown-toned adult moth with its distinct wing patterns.

Let’s understand the distinct physical characteristics across each life stage:

Caterpillar Stage

The larvae of this species exhibit a greenish hue on their bodies, punctuated by evenly spaced white bumps. Their heads are notably pointed. 

A unique behavior observed in these caterpillars is their ability to produce a “squeaking” sound

This sound is generated when they release air from their abdominal spiracles. This behavior serves a defensive purpose, aiming to startle and deter potential predators.

Pupa Stage

This is the transitional phase where the caterpillar undergoes metamorphosis to become an adult moth.

The pupa is the resting stage before the emergence of the adult form.

Adult Moth

Adult Walnut Sphinx Moths display sexual dimorphism, though it’s not highly pronounced. 

Their wings, when spread, reveal either a light or dark brown color. Some may have tinges of pink or white. 

Patterns on the wings can vary, being either distinct or faint. When the wings are folded, the coloration remains consistent, but the patterns appear slightly muted. 

These moths have an average wingspan ranging from 45 to 75 mm. Their flight pattern is described as erratic.

Eggs

Female moths lay their eggs in proximity to their host plants, typically soon after mating.

These eggs are relatively large, with their shape oscillating between round and oval.

Behavior and Ecology

The Walnut Sphinx Moth exhibits specific behaviors and ecological patterns that are integral to its survival and propagation:

Active Months

The moth is predominantly active from May through August. During these months, it engages in mating, laying eggs, and completing its life cycle.

Attraction to Light

Both male and female Walnut Sphinx moths are drawn to light sources. 

This behavior is evident as they frequently appear at light traps, making light an effective method for studying or observing this species.

Defensive Behaviors

The caterpillars have developed a unique defense mechanism. When they sense a threat, they produce a “squeaking” sound. 

This sound is created by expelling air from their spiracles. Along with this sound, they may also thrash about, aiming to startle and ward off potential predators.

Reproductive Cycle

In the northern states, the Walnut Sphinx Moth typically produces a single brood between May and August. 

However, in warmer southern regions, they can produce two broods within the same timeframe.

Distribution and Habitat

The Walnut Sphinx Moth is primarily distributed in North America. Its presence is notably dominant in Missouri and extends to states located east of the Rocky Mountains

The moth’s natural habitat is deciduous woodlands, where it thrives and reproduces. 

While it is commonly found in these woodlands, the Walnut Sphinx Moth displays adaptability by making appearances in various other habitats. 

However, it has not been observed in specific regions, like the Atlantic Coastal Pine Barrens. 

Walnut Sphinx

Diet

The larvae, or caterpillars, have a diet that primarily consists of leaves from walnut, butternut, hickory, alder, beech, hazelnut, and hophornbeam trees. 

In contrast, adult Walnut Sphinx Moths do not consume any food.

Reproduction and Life Cycle

The reproductive and life cycle processes of the Walnut Sphinx Moth are systematic and influenced by environmental factors:

Egg Laying

After mating, female moths lay their eggs near host plants. 

The proximity to these plants ensures that emerging caterpillars have immediate access to their primary food source. 

The eggs are sizable, with shapes ranging from round to oval.

Larval Stage

Once the eggs hatch, the larvae, or caterpillars, begin feeding on the leaves of their host plants. 

Their nocturnal feeding habits allow them to consume nutrients with reduced risk from daytime predators. 

During the day, they often rest along the mid-vein of leaves, blending in with their surroundings.

Pupation

After reaching maturity, the caterpillars enter the pupa stage, a transitional phase leading to their transformation into adult moths. 

This metamorphosis is a critical stage in their life cycle.

Walnut Sphinx

Adult Stage

Emerging as fully-grown moths, they engage in mating activities to continue the propagation of their species. 

While the northern regions typically see a single brood between May and August, the warmer southern areas can witness two broods within the same period.

Unique Features and Fun Facts

The Walnut Sphinx Moth, while a member of the broader moth family, possesses several distinct characteristics and intriguing facts:

Regional Variation

In Western Texas, a subset of this moth species displays a grayish hue, contrasting the typical brown found in other regions. 

This variation showcases the moth’s adaptability to different environments.

Larval Defense

Beyond the “squeaking” sound, the larvae exhibit fluorescence under UV light. 

This bright glow can be a deterrent to potential predators, making them easier to spot at night.

Dietary Flexibility

While the larvae have preferred host plants, there have been reports of them feeding on other plants. 

However, these claims require further validation through controlled studies.

Sensitivity to Conditions

In captivity, the Walnut Sphinx Moth larvae have shown sensitivity to humidity levels. Proper ventilation is crucial to ensure their well-being.

Single Genus Species

The Walnut Sphinx Moth is the only species classified under the genus Amorpha. This exclusivity highlights its unique position within the moth family.

Newly Eclosed Walnut Sphinx

Rearing in Captivity

Rearing the Walnut Sphinx Moth in captivity requires specific conditions and practices to ensure their healthy development:

Egg Collection

To obtain eggs, a female moth can be placed in a brown paper bag for several days.

A single female is capable of laying over 100 eggs during this period.

Larval Diet

The larvae predominantly feed on two genera: Carya and Juglans, which include species like Pecan, Black Walnut, and Pignut Hickory.

They also accept Ostrya (Hop Hornbeam) and other Juglandaceae plants.

Housing Conditions

The larvae need adequate space to thrive. In medium-sized containers, it’s advisable to house 3-5 larvae.

Larger containers can accommodate up to 50 larvae. Overcrowding should be avoided.

Humidity Management

The larvae are sensitive to humidity levels. Containers should be aired out daily to maintain optimal conditions.

Pupation

The paper towel method is effective for pupation. Alternatively, soil can be used as a pupation medium.

It’s essential to monitor the larvae during this stage and ensure they have the right conditions for metamorphosis.

Newly Eclosed Walnut Sphinx

Frequently Asked Questions

What does Amorpha Juglandis eat?

The Amorpha juglandis (walnut sphinx) caterpillar eats the leaves of many trees, including: 
Walnut and butternut (Juglans)
Hickory (Carya)
Alder (Alnus)
Beech (Fagus)
Hazelnut (Corylus)
Hop-hornbeam (Ostrya)

What is the North American walnut sphinx moth caterpillar?

Caterpillars belonging to the Amorpha juglandis species are also called hornworms. They have strong, stubby legs that can clamp onto plants, a small horn at the back, and a sizeable, vibrant body. The caterpillar frequently has the appearance of a sphinx when it is perched on a branch. The monotypic moth genus Amorpha, which is in the family Sphingidae, only contains one species, the Amorpha juglandis. Its wingspan ranges from 4.5 to 7.5 cm, or 1 3/4 to 2 15/16 inches. The adult moth can be brown, white, or pink in color and ranges in length from 45mm to 75mm (1.77″ to 2.95″).

Conclusion

In summary, the Walnut Sphinx Moth, native to North America, is a unique insect with a rich history, first described in 1797. 

Classified under the Sphingidae family, its life cycle encompasses distinct stages from egg to adult. 

Primarily found in deciduous woodlands, its larvae feed on specific host plants like walnut and hickory. 

The moth displays intriguing behaviors, such as attraction to light and a larval “squeaking” defense mechanism. 

Regional variations exist, with some moths in Texas exhibiting a gray hue. Rearing in captivity demands specific conditions, especially concerning humidity and space. 

This moth’s distinct characteristics make it a fascinating subject of study.

Reader Emails

Over the years, our website, whatsthatbug.com has received hundreds of letters and some interesting images asking us about these insects. Scroll down to have a look at some of them.

Letter 1 – Walnut Sphinx

 

Moth
I look at your bug page just about everyday and enjoy everything about it, I came across this moth a while back and can’t ID it and thought maybe you could help. I live right outside San Antonio, Texas. Thank You…



This is a positively beautiful photograph of a Walnut Sphinx, Amorpha juglandis, which can be found on Bill Oehlke’s excellent website.

Letter 2 – Walnut Sphinx

 

Big Brown Moth Location: Houston, Texas March 21, 2011 9:41 pm I found this very large moth on the outside of the house in the afternoon, September 11 2009. I thought it was a weirdly stuck leaf but, on closer inspection, it turned out to be a cool moth. It seemed really docile and allowed me to pick it up and mess with it without reacting very much. I brought it inside with me and set it on a plant inside. It started acting up right then, sprayed a white fluid out of it’s rear end and started flying around. I had gotten some of the white fluid on me so it washed it off while the giant insect tried to escape. I eventually got it out of the house but not after chasing it all over and losing track of it a few times. I found this website recently and I wondered if you could tell me what sort of moth it was and what it sprayed at me. Signature: Thanks, Kelly Bufkin
Walnut Sphinx
Hi Kelly, Your moth is a Walnut Sphinx, Amorpha juglandis, and you can verify that by looking at the images on the Sphingidae of the Americas website.  Bill Oehlke writes:  “The adults are also highly variable; sometimes wings of an individual may be all one color or may have several colors, ranging from pale to dark brown, and may have a white or pink tinge. Patterns range from faint to pronounced.”  We have never heard of a Sphinx Moth spraying, and we suspect the fluid it exuded may have been a residual product of metamorphosis.
Walnut Sphinx
I looked through the moths people had sent in before and I saw a lot of other kinds of sphinxes.  They did look like my moth but not quite, haha.  For it to spray at me I must have scared it or something.  Thank you for identifying it!

Letter 3 – Walnut Sphinx

 

Moth in West Virginia Location: Cabins West Virginia July 18, 2011 3:47 pm While on vacation in Cabins, West Virginia last week I had some company waiting on the front porch one morning. I believe one moth was the Imperial Moth and the other one remains a mystery to me. Any help you may be able to give me would be greatly appreicated. I am so glad I found your site it it WONDERFUL! Signature: Priscilla
Walnut Sphinx
Dear Priscilla, You are correct about the Imperial Moth and the other is a Walnut Sphinx, Amorpha juglandis, which we verified by researching it on the Sphingidae of the Americas website.

Letter 4 – Walnut Sphinx

 

Moth that looks like a leaf? Location: Oklahoma City August 23, 2011 8:32 am This moth is on my house, right outside the front door. It’s very cool, looks like oak leaves! 🙂 What is it called? Signature: Elizabeth
Walnut Sphinx
Hi Elizabeth, This interesting moth is a Walnut Sphinx, Amorpha juglandis.  You can verify our identification on the Sphingidae of the Americas website.

Letter 5 – Walnut Sphinx

 

Subject: Poplar Hawkmoth in Texas? Location: Wise County, Texas July 9, 2013 9:36 am Photographed this today just off my deck – I’m in Wise County, Texas. It looks like the UK moth, but this is Texas! Have they moved here, or is this a related species? Thanks! Signature: Mary
Walnut Sphinx
Walnut Sphinx
Hi Mary, Your moth is in the same family, Sphingidae, as the Poplar Hawkmoth.  This is a Walnut Sphinx, Amorpha juglandis, and according to the Sphingidae of the Americas:  “The adults are also highly variable; sometimes wings of an individual may be all one color or may have several colors, ranging from pale to dark brown, and may have a white or pink tinge. Patterns range from faint to pronounced.” Hey, Daniel! Thank you so much for your quick response.  I love its name!  It’s gone off to wherever moths fly away to, but I truly enjoyed seeing it – what a beauty! Mary

Letter 6 – Walnut Sphinx

 

Subject: Moth identification Location: Mid-Michigan January 13, 2016 2:16 pm I found this moth in my laundry tub in the late Summer/Fall. It was found in mid-Michigan. Our home is located in the countryside and boardered by a creek. Signature: Charli
Walnut Sphinx
Walnut Sphinx
Dear Charli, This impressive moth is a Walnut Sphinx.  You can read more about it on the Sphingidae of the Americas site. Thank you so much for your quick response. I will tell others about your website!

Letter 7 – Walnut Sphinx Caterpillar

 

Hissing Catapillar Location: Ft. Hood, TX October 19, 2011 1:02 pm This catapillar started hissing when my wife tried to move it away from her chair. What is it? Signature: Brian
Walnut Sphinx Caterpillar
Hi Brian, This is the caterpillar of one of the Sphinx Moths or Hawkmoths.  The head and caudal horn are very distinctive in your individual, and we believe this may the the caterpillar of the Walnut Sphinx, Amorpha juglandis.  There are photos on the Sphingidae of the Americas website that show the similarities and there are also some similar photos on BugGuide which notes:  “larva may produce a whistle-like hiss when handled.”  We will contact Bill Oehlke to see if he can confirm or correct. Bill Oehkle responds Yes it is Amorpha juglandis, the walnut sphinx.

Authors

    by
  • Bugman

    Bugman aka Daniel Marlos has been identifying bugs since 1999. whatsthatbug.com is his passion project and it has helped millions of readers identify the bug that has been bugging them for over two decades. You can reach out to him through our Contact Page.

  • Piyushi Dhir

    Piyushi is a nature lover, blogger and traveler at heart. She lives in beautiful Canada with her family. Piyushi is an animal lover and loves to write about all creatures.

5 thoughts on “Walnut Sphinx Moth: All You Need to Know”

  1. I found this Post as a result of searching for a similar incident. My students found a Small-eyed Sphinx moth and when I allowed it to walk on my finger it began to vibrate and shoot out quite a large amount of white liquid. The spray on my shorts dried quickly, leaving a permanent bleached out stain! The moth continued to gyrate for another 20-30 seconds then flew away.

    Reply
    • Until we learn otherwise, we are going to stick to our original assumption that the spray was a residual product of metamorphosis.

      Reply
  2. I found this species at my primary school at Melbourne Australia when I was in prep on this following date 3-08-2011 at 1:16 pm at my play time so they called the national Australia wildlife welfare Australia. So I found this first and it was hissing at me when I picked it up and it had eyes like a human being and when I was touching it felt like leather so it was an interesting journey.

    Reply
    • The Walnut Sphinx is not native to Australia. Other Sphinx Moth caterpillars native to Australia might have similar behavior.

      Reply
  3. Hello,
    I have a mournful sphinx moth, for several days now and he has done the same. At first it was a red/pinkish liquid, then the next couple times it was clear. (I also have bleached spots on my shirt and was just wondering when I got bleach on it- which I don’t think I did)
    I would be happy to get a video of him doing this if you’d like to send to you! I’m not sure, but I didn’t think they would continue to expel liquid from metamorphosis for multiple days.
    I felt it was a defense mechanism, as he always starts warming his wings at basically the same time.

    Reply

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