Hubbards Silkmoth: All You Need to Know for Enthusiasts and Curious Minds

Hubbard’s Silkmoth, part of the giant silk moth family (Saturniidae), is known for its captivating appearance and fascinating biology. These moths, like other Saturniids, are typically nocturnal and embark on their journey through life with one main purpose: reproduction.

As adults, Hubbard’s Silkmoths do not eat due to their vestigial mouthparts and lack of a gut. Instead, they rely on the lipids stored during their caterpillar stage for nourishment. This unique feature makes their adult lives quite intriguing and often short-lived, as they focus on finding mates and laying eggs. Their caterpillars are prone to being preyed upon by parasites, while the adult moths face threats from owls and bats.

Overall, Hubbard’s Silkmoth is a captivating species that offers a unique glimpse into the world of nocturnal insects. By understanding their life cycle and the challenges they face, we can appreciate their beauty and the important role they play in nature.

Hubbard’s Silkmoth Basics

Identification and Appearance

Hubbard’s Silkmoth (Sphingicampa hubbardi) is a moth belonging to the family Saturniidae, which comprises various giant silk moths. Key features of this moth include:

• Large, often colorful wings
• Distinct eye-like patterns on the wings
• Wingspan can range from 3 to 6 inches

The appearance of Hubbard’s Silkmoth can serve as a useful example when comparing it with other moths within the Saturniidae family.

Classification and Species

Hubbard’s Silkmoth is part of the Animalia kingdom, the Arthropoda phylum, and the Insecta class. Here is a brief classification of this species:

• Kingdom: Animalia
• Phylum: Arthropoda
• Class: Insecta
• Order: Lepidoptera
• Family: Saturniidae
• Genus: Sphingicampa
• Species: S. hubbardi

Syssphinx is another genus within the Saturniidae family and shares similar traits with Hubbard’s Silkmoth.

The following comparison table illustrates some differences between Hubbard’s Silkmoth and other species within the Saturniidae family:

Keep in mind that characteristics can vary even within the same species, so the information provided here serves as a general guide.

Life Cycle and Habitat

From Caterpillar to Adult Moth

Hubbard’s Silkmoth goes through a standard life cycle:

• Eggs: The female moth lays eggs on suitable host plants.
• Caterpillar: The eggs hatch into larvae, feeding on leaves.
• Pupa: The caterpillar forms a cocoon and pupates inside.
• Adult Moth: Moths emerge from cocoons with distinctive hind wings.

This process typically occurs over a span of weeks, depending on environmental conditions. Examples of host plants for Hubbard’s Silkmoth caterpillars include mesquite and acacia trees. During winter, some caterpillars overwinter as pupae in their cocoons, waiting for favorable conditions to emerge as adult moths.

Habitat and Range

Hubbard’s Small Silkmoth is found across various regions in North America. Their habitat ranges from California, Texas, Arizona, New Mexico, and extends into Mexico. The moth prefers a mix of landscapes – from open grasslands to wooded areas. The caterpillars feed mainly on mesquite and acacia leaves, making these host plants essential components of their habitat.

Host Plants and Food Sources

Mesquite and Acacia Trees

Hubbards Silkmoth (Subfamily Ceratocampinae) primarily feeds on Mesquite (Prosopis spp.) and Acacia (Cercidium microphyllum) trees. Here are some key points on these host plants:

• Mesquite trees, especially Honey Mesquite (Prosopis glandulosa)
• Acacia trees, specifically Catclaw Acacia (Acacia greggii)

These trees provide essential nutrients for the moth’s growth and survival.

Herbivore Diet

As an herbivore, Hubbards Silkmoth’s diet consists specifically of plant material from Mesquite and Acacia. Examples of their diet include:

• Leaves
• Plant stems
• Flower buds

These components offer necessary nourishment, including vitamins, minerals, and fibers.

Comparison of Host Plants

Overall, both host plants are of great importance to Hubbards Silkmoth, assisting them in obtaining adequate nutrition from leaves, plant stems, and flower buds. These resources are especially crucial for sustaining their growth, reproduction, and survival.

Mating and Reproduction

Attracting Mates and Courtship

Hubbards Silkmoths utilize visual and chemical cues to attract mates. Females release pheromones, while males use their antenna to detect them. Males also tend to have a larger size and antenna compared to females, which may play a role in attracting females.

Males and females can be identified by their distinct color patterns. Here are a few differences:

Female Hubbards Silkmoth:

• Light gray to brown color
• Red-pink markings with white dots
• Size: Approximately 3 inches in length

Male Hubbards Silkmoth:

• Darker gray color
• Red-pink markings with a more continuous pattern
• Size: Slightly larger, up to 3.5 inches in length

Female and Male Differences

Males and females also differ in their reproductive behaviors. Once a male detects the female’s pheromones, he’ll approach her and initiate courtship. During courtship, males often flutter their wings while females remain still. After a successful courtship, male and female Hubbards Silkmoths will copulate, ensuring the continuation of their species.

In summary, Hubbards Silkmoths have unique visual and chemical mating cues, and their colors and patterns help distinguish males from females. The different behaviors exhibited during courtship and the distinct characteristics between males and females are essential factors for the successful reproduction of these moths.

Defense Mechanisms and Predators

Antipredator Adaptations

Hubbards Silkmoths employ various antipredator adaptations:

• Black spot: Found on the undersides of the wings, these spots mimic the eyes of a larger creature, deterring predators.
• Camouflage: Older caterpillars and adult moths blend in with their surroundings, avoiding detection by predators.

These adaptations provide protection and improve the moth’s chances of survival.

Common Predators

Common predators of the Hubbards Silkmoth caterpillars and adults include:

• Ants: Known to attack at the petioles and leaf bases.
• Larger insects: Can prey on older caterpillars, overcoming their horns for defense.

Comparison Table

Human Interactions and Conservation

Hubbards Silkmoth in Research and Literature

The Hubbard’s silkmoth, also known as the mesquite moth, belongs to the family of moths found across the U.S. and Canada. It has been widely studied by entomologists at institutions such as the University of California Press. In the book “Moths of Western North America,” the moth’s habitat, characteristics, and behavior are thoroughly examined.

Characteristics of the Hubbard’s Silkmoth:

• Typically found in arid regions
• Tends to inhabit mesquite trees
• Distinct coloring and pattern on wings
• Known for the caterpillar’s silk-spinning abilities

Conservation and Population Status

Due to habitat fragmentation and human activities, the conservation status of the Hubbard’s silkmoth is a point of concern. Below is a comparison of the moth’s habitat in various regions:

Efforts to protect and maintain the moth’s habitat are critical in ensuring its survival. Researchers and conservationists continue to assess the population status, evaluate potential threats, and devise strategies to ensure the long-term preservation of this unique species.

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 – Hubbard's Small Silkmoth Caterpillar

Odd Caterpillar
Sir,
My son’s and I located this odd looking caterpillar. It is purple and green with horns. It also has silver spikes on it’s back. We were wondering if you would be able to identify what it is. We have attached a few photo’s as well. Thank you for your time.
Michael

Hi Michael,
We are going to very gently inform you about how crucial it is for you to provide us with location information when submitting an identification request. We are certain this is a moth in the genus Syssphinx, most probably the Hubbard’s Small Silkmoth, Syssphinx hubbardi. It ranges from Arizona to West Texas. It is also found in extreme east California and south Nevada. If you live in central Texas, it is probably a closely related species, Syssphinx heiligbrodti.

Mr. Marlos,
I apologize, we live in Tucson, Arizona. I would also like to know if they are poisonous or if they sting.
Michael

Hi again Michael,
Thanks for writing back with your location. These caterpillars neither sting, nor are they poisonous. The frightful appearance is a protective device.

Letter 2 – Mesquite Moth Caterpillar

Hickory Horned Devil Relative?
This roughly two inch bugger was hanging out on a rock under a mesquite tree in our yard in Tucson, AZ. It was quite regal with all the shiny silver spots down it’s back. I was looking at the home page and it seems like this guy might be related to the HHD perhaps? Just ran across your site last week after my pregnant wife yelled out from our bathroom, “Aaaagh! Hey get in here! What are these giant sized maggot things crawling all over the bathroom floor.” I’m still not 100% sure if they were hornets or yellow jackets, but had to remove them. (They were nesting in the bathroom vent ductwork and the larvae were crawling down the pipe and then falling from the ceiling.) Keep up the great work! By the by, it’d be great if there was a way to leverage all the data to create a self-identification process. I recall from my Microbiology days constructing decision trees for identifying bacteria species. Similar idea here for snakes.
http://www.spiritone.com/~brucem/garter.htm
It’d be cool if a user could answer a few rule-based questions and then get photos and names to compare as “potentials”. Sorry for the detail, just the geek in me thinking too hard. Cheers,
Timo

Hi Timo,
We needed to research this guy, but we quickly were lead to a photo of Sphingicampa hubbardi, the Mesquite Moth Caterpillar. The moth is also known as Hubbard’s Silkmoth. The caterpillar is gorgeous, and it is one of the Saturnidae and the same subfamily, Citheroniinae, as the Royal Walnut Moth or Hickory Horned Devil. We did find a website with some information.

Letter 3 – Hubbard's Silkmoth Caterpillar

Unknown Beautiful Caterpillar
Dear WTB,
My 2-year old daughter discovered this caterpillar amongst “Primrose” jasmine and “Barbara Karst” bougainvillea here in Tucson, Arizona on Sep. 30, 2006. After being “captured”, it was offered jasmine and appeared uninterested. However, it seems to enjoy eating the bougainvillea. The color seems a little off in this photo. Its underside, head, and rear-end are leaf-green; its back and sides are maroon. The teardrop shaped “spikes” on each section of the body are metallic silver on the topsides and red-tipped white on the undersides. The “bumps” that line each section of the body are metallic gold. It is absolutely beautiful and, unfortunately, I have so far been unable to get a picture of it which does it the slightest bit of justice. My daughter absolutely loves the little critter and so we have given it a home in a large “bug house”. I’m not really sure how to care for it, but I have equipped it with a rigid stick for climbing, a damp cotton pad for moisture, and bougainvillea leaves for food. If you are able to tell me, I would be greatly interested in learning what kind of caterpillar it is, what it will become, and how best to care for it. I think it would be great if my daughter could witness its metamorphosis before we release it back outside. Thank you!
Janet

Hi Janet,
This is a Hubbard’s Silkmoth or Mesquite Moth Caterpillar, Sphingicampa hubbardi. The caterpillars food plants are listed as acacia and mesquite. Perhaps you have one of those nearby. If not, it seems we might be able to add bouganvilla to the list of host plants. The adult moths are grayish brown with rosy pink hind wings. We would love to recieve a photo of the adult if the metamorphosis is successful.

Letter 4 – Hubbard's Small Silkmoth Caterpillar

Sphingid Larva
April 9, 2010
Picture taken last summer in our yard in Tucson, Arizona. I remember looking it up and found it once, but lost the ID. I think it fed on ironwood. Found a couple specimens crawling around. Can’t remember the month, but thinking it was late summer. Most distinctive were the mirror-like scales running the length of the body.
Lisa Rakestraw
Tucson

Dear Lisa,
Despite the name Syssphinx hubbardi, the Hubbard’s Small Silkmoth Caterpillar is not a Sphinx in the family Sphingidae, but a Royal Moth in the tribe Ceratocampinae.  BugGuide reports this species from Arizona and New Mexico, though it is also known from California, Nevada and Texas.

Letter 5 – Hubbard's Small Silkmoth Caterpillar

Thorny Tucson caterpillar
Location: East Tucson, AZ
September 30, 2011 10:48 pm
What is my bug?
Signature: Curious in tucson

Dear Curious in Tuscon,
Your caterpillar is in the genus Syssphinx, and it is most likely Hubbard’s Small Silkmoth, Syssphinx hubbardi.  You can compare your photo to images posted on BugGuide which indicates:  “Larvae feed on Wright’s acacia, honey mesquite and catclaw acacia”.

Letter 6 – Possibly Hubbard’s Small Silkmoth Caterpillar

Subject:  Caterpillar ID
Geographic location of the bug:  SW North America (AZ desert)
Date: 09/28/2021
Time: 12:11 PM EDT
Your letter to the bugman:  We found this Sept, 27 early evening in New River, AZ (2,000 ft elevation).  I have not found anything like it in my searches.  The shiny silver barbs on its back come out when agitated.
How you want your letter signed:  DC

Dear DC,
This is a Silkmoth Caterpillar in the genus Syssphinx, possibly a Hubbard’s Small Silkmoth Caterpillar.  Here is a BugGuide image for comparison.

Letter 7 – Prepupal Hubbard’s Silkmoth Caterpillar

Subject: What is this bug
Location: Tucson AZ
September 10, 2015 11:59 am
I work at a dog kennel and I have I have found a lot of them out in my dog runs I Just want to make sure they are not poisonous.
Signature: Jonathan

Good morning Jonathan,
This is a pre-pupal caterpillar from a moth in the genus Sphingicampa, formerly Syssphinx, and we suspect it is most likely a Hubbard’s Silkmoth, Sphingicampa hubbardi, though another species, Sphingicampa raspa, is also found in Arizona.  According to BugGuide, the Hubbard’s Silkmoth:  “Larvae feed on Wright’s acacia, honey mesquite and catclaw acacia.”  They are not poisonous.