Carnegie Museum of Natural History

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caterpillars

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Deck the Trees with Moth Cocoons

By Vanessa Verdecia

cocoons

Many people wonder: “what happens to bugs during the winter months?”  In the case of Callosamia promethea, known as the Promethea Moth, the caterpillars will have spun a cocoon in a leaf and will spend the winter as a pupa in a cocoon that is well attached by silk and hanging from a tree.  This is the third stage of metamorphosis before the adult moth ecloses (=emerges) the following summer and is seen flying during June-July in Pennsylvania.  You may look for these cocoons in the winter as they are usually found on low-hanging branches of many types of forest trees.

This year in Invertebrate Zoology we reared Promethea caterpillars and we are now ready to mimic winter conditions in the lab. The live cocoons have been carefully stored in a sealed plastic bag with a damp paper towel to maintain humidity.  This bag has been stored in the refrigerator to mimic the cold temperature that the cocoons would have experienced outside.  Insects are sensitive to temperature cues that will dictate when the moth is ready to eclose.  Experiencing diapause—a period of suspended development—will trigger the moths to eclose the following year.  The cocoons will remain in the refrigerator until next spring, and hopefully they will survive and we’ll have some beautiful moths eclose.  Insects are also dependent on light cues and are sensitive to day length, which is more difficult to mimic in a lab setting.  I am hopeful these will survive, as this technique has worked in the past.

many cocoons

This process will conclude the full cycle of an isofemale rearing in which all of the stages of metamorphosis were observed and documented.  We have the wild-caught male and female adult parents.  At each stage of development, specimens were chosen to be preserved in order to document the egg, larval, and pupal stages.  These specimens serve as a reference for associating the developmental stages of a single species, as documented in a reared culture from a single parent.

egg, larvae, and cocoon specimens

Go ahead and look around because this is the perfect time of the year to see Promethea moth cocoons decking the trees of the forest this holiday season!

Vanessa Verdecia is a collection assistant in the museum’s Invertebrate Zoology Section. Museum employees are encouraged to blog about their unique experiences and knowledge gained from working at the museum.

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What is a caterpillar database?

What is a caterpillar database? Curatorial Assistant in Invertebrate Zoology Catherine Giles introduces the larval collection and how it is organized. Learn how the section of Invertebrate Zoology collects and pickles specimens, then how they are stored and matched to a digital database of images and written notes.

Ask a Scientist is a video series where we ask our research staff questions about the millions of amazing objects and specimens stored in our museum collection. Tune in on YouTube, and submit your own questions via Twitter @CarnegieMNH!

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The Very Hungry Promethea Caterpillars

by Vanessa Verdecia

promethea moth eggs

These Promethea Moth (Callosamia promethea) eggs were laid in clusters by a single female parent.  When the caterpillars first hatched they measured approximately 3mm in length and as the caterpillars grew, they shed their skin and molted through a series of stages referred to as instars.  Each one of these instars varies in appearance.  Early instars are gregarious and remain together on the underside of the leaves.  

promethea moth caterpillars
promethea moth caterpillars

In the earlier instars the Promethea Moth caterpillars have a black and yellow banded appearance.  In contrast to these earlier stages, the body of the last instar caterpillars are pale green and they are recognized by the protruding, bright red knobs that are located on the thoracic region as well as the yellow knob found on the eighth abdominal segment.  The final instar caterpillars in this culture measured up to 4.5cm in length in a resting position, but they can measure up to 6cm when active and stretched out.

promethea moth caterpillar

The Promethea Moth is a member of the family Saturniidae, a group known as the Giant Silkworm moths. In this group of moths, the mouth parts are reduced and the digestive tract is absent, which means they do not feed as adults.  Most caterpillar species are big eaters, but in families like Saturniidae, the adult moths rely heavily on all the energy stored while eating in the larval stages.

Raising caterpillars in the lab is a labor of love.  Caterpillars depend on having fresh food and a clean environment that is created by housing the live caterpillars in plastic chambers that help preserve the moisture in the leaves.  This culture was reared on sweet gum, but Promethea Moth caterpillars will feed on many different trees.  The caterpillars hatched on 8-June-2018 and some of the specimens in the final instars were seen spinning their cocoons on 17-July-2018.

caterpillars on sweet gum

The caterpillars produce silk on a leaf and the petiole and spin a cocoon with the leaf wrapped around it. After the caterpillars spin their cocoons, they will enter the pupal stage and overwinter until the late spring or early summer of 2019, however, a partial second generation in the summer is known to occur in Pennsylvania.  Cocoons attached to the hostplant by the silk can be seen in the winter when all the other leaves have fallen.

cocoon

Vanessa Verdecia is a collection assistant in the museum’s Invertebrate Zoology Section. Museum employees are encouraged to blog about their unique experiences and knowledge gained from working at the museum.

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Eacles imperialis

imperial moth caterpillars (Eacles imperialis)

by Vanessa Verdecia

A culture of imperial moth caterpillars (Eacles imperialis) was reared on oak leaves this summer in Carnegie Museum of Natural History’s Section of Invertebrate Zoology. This species is common in Pennsylvania and belongs to the giant silkworm moth family known as the Saturniidae. The caterpillars occur in various color forms including green, brown, red, and pink, but they all have long setae (“hairs” as seen in the image) and pronounced white spots along the side. All the ones in this culture were brown. The larvae occur from July through September, and there is one generation this far north. The adult moths should eclose next year—late spring or early summer.

Vanessa Verdecia is a collection assistant in the museum’s Invertebrate Zoology Section. Museum employees are encouraged to blog about their unique experiences and knowledge gained from working at the museum.