Carnegie Museum of Natural History

One of the Four Carnegie Museums of Pittsburgh

Lepidoptera

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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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Is this butterfly blue or green?

by Vanessa Verdecia

blue butterfly

An image of a beautiful “blue” butterfly.  What kind is it, they asked me?  That’s not always an easy question to answer.  The first thing I knew was that this butterfly was in the family Papilionidae. That determination was made based on the tails seen on the hindwings, giving the family its common name of Swallowtail butterflies.  It’s a good thing the Carnegie has a wonderful reference collection of butterfly specimens that is also complemented with an extensive library of scientific literature that should give me a good shot at figuring out what this beautiful specimen might be.

I started with some of the amazing picture books in the library because all I had was a single image of a specimen to identify with no visible clues from the image that might show what region of the world the specimen was collected from.  After searching through the historical collection for curated and identified specimens to compare to the image, and perusing through dozens of drawers of mixed swallowtail butterflies that might contain similar specimens, I was almost certain the specimen in the picture was a Papilio blumei, also known as the Green Swallowtail.  Hmmm, the Green Swallowtail? The wing shape and pattern of the markings on the wings were a match, but the picture I had was of a butterfly with blue markings, not green!  All the specimens of this species in the collection looked green.

green butterfly

Then I thought: I bet this unusual color has something to do with the structural coloring in the scales of the wings.  The reason the butterfly looked blue in the image was because the picture was taken in the dark and the photo was shot at an angle. This caused the butterfly to appear blue because the microscopic scales of the wings are structured in such a way that they interfere with visible light.  When I held my hand over the specimen and cast a shadow on it, the green bands then appeared blue, just like in the picture.  Structural coloring like this is seen in many insects and other animals, and can often be iridescent.

blue butterfly and green butterfly that are actually the same butterfly from different angles

The next step was to confirm the identification with Dr. Rawlins, our expert on Lepidoptera (moths and butterflies).  This is where it got tricky.  According to the literature, Papilio blumei consists of four distinct subspecies that represent geographical variants of that species. When looking at specimens in the collection, there are subtle differences in the width of the blue bands on the wings. The photograph I had matched specimens that were identified in the collection as Papilio blumei.  This species is only known from the island of Sulawesi (Indonesia). Differences found among specimens from different regions of the island appear to correspond with the different subspecies. A careful detailed study would have to be done in order to revise this species complex.

Sorting out all this tricky stuff is the science of taxonomy, which is the branch of science that deals with the classification and naming of organisms.  Species are classified according to the various characteristics they have in common, which helps scientists to understand how organisms are related to one another.  A deeper understanding of these different characters and how they evolved over time and in concert with a species life history, is what constitutes the study of systematics, which is the field of study that deals with evolutionary relationships among organisms.

There are over 1 million described insect species on earth, and many more sitting in collections all over the world, still waiting to be “discovered”.  Some of these specimens hidden away in the collections are known to be new species and are in the process of “getting a name”—a common phrase heard around museum insect collections that refers to the process of describing in detail the defining characteristics of the species, assigning a Latin name to the specimen(s), and formally publishing the name in the scientific literature.  Getting to put a name on a new species is one of the best things about working in a museum. Knowing how many specimens there are to work on, or the possibility of stumbling across a lost or forgotten species someday while working in the collection is truly exciting.  In a collection containing an estimated 30,000 drawers and roughly 14.5 million specimens, you never know what you might find!

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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Illustrating the Head of an Inchworm (caterpillar of Lepidoptera: Geometridae)

by Jane Hyland

scientific illustration of an inchworm

Teamwork between scientists studying insects (entomologists) and illustrators is an important part of museum-based scientific research.  This important collaborative aspect between the scientist and the illustrator is instrumental in identifying and clarifying important characteristics of the specimen for identification purposes. Scientific illustration allows observers to see and study certain tiny features that are barely visible under the microscope, but which the scientist is familiar.

By studying and illustrating distinctive morphological features of specimens, the illustrator can choose to emphasize or ignore entirely different characters, increasing the visibility of important structures for accurate identification. For example, the placement of tiny sensory hairs (setae) on the head of this common moth caterpillar (inchworm) may be emphasized by the illustrator as important for identifying this species.

Jane Hyland is a Scientific Preparator at the Carnegie Museum of Natural History. Museum employees are encouraged to blog about their unique experiences and knowledge gained from working at the museum.

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The Significance of Raising Caterpillars

By Vanessa Verdecia

Imperial moth

The Imperial moth (Eacles imperialis) is a member of the Saturniid family, a group also known as the Giant Silkworm Moths.  This specimen is one of several that was reared from eggs laid last year. The corresponding larva (caterpillar) can be seen in this 2017 blog post.

Lepidoptera (moths and butterflies) develop through a process known as complete metamorphosis. They go through four distinct stages: egg, larva, pupa, and adult.  Entomologists use isofemale culture rearings to document these stages in a wide variety of different species.  In isofemale cultures, wild-caught females are kept in isolation until they have laid their eggs. The resulting larvae then represent one known species derived from a single individual. This method eliminates the possibility of accidentally rearing two or more different species together.

Recording the growth and development of caterpillars is important to understanding the natural history of a species. Detailed notes tell the story of the species being reared. For example, we can document the time of year that adults are found and when eggs are laid, food preferences of the larvae, and whether adults eclose from the pupae in the Fall or overwinter until the Spring before starting the cycle all over again.  Even though laboratory conditions may affect the timing of these changes, the specimens preserved still serve as vouchers to represent stages associated with each species.

The Section of Invertebrate Zoology’s Lepidoptera larval collection serves as an incredible library of associated eggs, larvae, pupae, and adult stages for many species documented through extensive isofemale culture rearings. The corresponding notes serve as a valuable resource for life history information, such as host plant preferences.  Host records are important since a given species will survive on only certain types of host plants.  The caterpillars of the Imperial moth will eat a variety of deciduous trees and this specimen was reared on oak.  However, some species may be host specific and only survive when given the correct plant to eat.

Imperial moth

The larvae of Imperial moth caterpillars reared last year overwintered in the pupal stage.  Winter conditions were provided by storing the pupae in containers kept in the refrigerator through the winter.  The containers were removed and placed at room temperature and we are now enjoying the adult Imperial moths that have been eclosing since May and June.  Many images have been taken, and multiple voucher specimens were preserved to fully document this species in the museum’s reared larval collection.

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.