Pachylia ficus
Fig Sphinx Caterpillar

Pachylia ficus caterpillar courtesy of Beatrice Cruz and students,
elementary school science lab in Harlingen, Texas.

Pachylia ficus caterpillar courtesy of Beatrice Cruz and students,
elementary school science lab in Harlingen, Texas.

On October 17, 2007 Breatrice writes,

"Dear Bill:

"My name is Beatrice and I teach at an elementary in Deep South Texas, Harlingen, Texas. We have a science lab and I run the lab. We started this lab last year and it has become something very exciting on campus. Ever since I started running the lab, students have been bringing me all kinds of bugs and small creatures.

"Iíve made a huge bulletin board of various butterflies and moths that I have found or that other teachers and students have brought me. (Iíve enclosed those pictures).

"I try to research about the butterfly or moth and find a picture of the caterpillar that it used to be. The students really enjoy bringing me new animals.

"The reason I am writing is because I had a student bring the biggest orange caterpillar I have ever seen in my life. (Iíve also enclosed pictures.) Itís about 4Ē long.

"I finally came across your website and found out that it is a Ficus Sphinx. Iím so excited to be able to report tomorrow what it is. My question is now how can I create an ďenvironmentĒ where the students can watch this caterpillar morph into a moth. This would be such a wonderful experience if I could get it to happen.

"Please let me know what I can do and any additional information about this creature. Thank you so much for all the work you are already doing."

***

I very much appreciate Beatrice's efforts to make the lab come alive for her students. I am sure there are things they will see and learn that will remain with them for the rest of their lives.

Most images of Sphingidae larvae (caterpillars) that I receive are of mature caterpillars that are ready to pupate.

The larvae are quite noticeable at that time due to their relatively large size, or due to their situation: 1) they might be near the end of a plant twig where they have just devoured five or six leaves, rendering them quite visible, or 2) they may have left the plant and are crawling around on the ground, seeking some soft earth so that they can excavate a subterranean chamber in which to pupate.

Birds love to eat caterpillars, and the avians probably find a great many meals at this time in a caterpillar's life.

To rescue the caterpillar from a possible trip down a bird's gullet and watch it transform first into a pupa and then into a moth or butterfly, there are a few simple but important steps to follow.

1) Handle the caterpillar as little as possible. Most caterpillars, especially those of the Sphingidae, are completely harmless to humans, but there are some spiny or even hairy ones from other families that can sting or cause an allergenic reaction. It is best to pick the caterpillar up with its feet and your fingers firmly attached to a twig. If that is not possible, then allowing it to crawl onto a piece of paper or twig or into a jar or cup is prefered.

2) Have a look at the immediate surroundings and take note of the foodplant(s) the caterpillar has been eating or might have been eating. If the caterpillar was found on a branch or stem and it is still feeding and growing, them some leaves, still affixed to the stem should be brought into the lab with the caterpillar. Many caterpillars will only eat specific plants.

3) A good habitat for rearing and observing is a nice sized glass jar (quart or litre sized or bigger), or a clear plastic tub, aquarium, etc.

Caterpillars require very little air, but they do need to take in moisture from their food. For that reason it is best to rear them and watch them develop in an airtight container. They will not suffer from lack of air and the closed environment will conserve the moisture content of the foliage (leaves) they might continue to eat.

Many people try to rear the caterpillars in a jar with a cloth or screen top, or the people punch holes in the jar lid. Sometimes this works, but it is not necessary, and it can actually be detrimental to the caterpillar if the leaves lose too much moisture.

4) The rearing container should be cleaned out at least every other day and fresh leaves should be offered so that developing caterpillars are never without food. Again, handle the caterpillars as little as possible. You can carefully empty the contents of the jar onto a piece of newspaper on a counter or desk top, then thoroughly clean out the jar and dry the insides of the jar, if it has been washed. Put in some fresh leaves, still affixed to the twig and carefully put the caterpillar back into the jar, preferably still attached to a leaf or stem. The caterpillar will crawl onto the fresh food soon enough.

5) The Sphingidae caterpillars do not spin silken cocoons when they are mature. Instead, most of them will leave the host plant and will crawl on the ground and seek some soft earth in which to dig an earthworm-like hole. Sometimes they dig down to a depth of six inches, squirm around and compact the soft earth so that they have a nice comfortable chamber in which to pupate. Often, however, they will pupate amongst leaf litter on the surface or excavate a much more shallow tunnel/chamber.

6) You can watch what typically goes on under the earth by placing the mature caterpillar in an antfarm-like structure, i.e., two pieces of upright glass in a frame sandwiching some loose soil. It is much easier, however, just to place the mature caterpillar in a tub, jar, bucket, etc., with a paper towel loosely folded and placed on the bottom of the container.

7) You can tell when the caterpillar is mature by its behaviour. When it stops feeding, leaves the foliage and crawls around the bottom of container, it is looking for a safe haven, and that is the time to move it to the housing described above.

8) The caterpillar will usually crawl under the paper towel, give off considerable moisture, and shrink noticeably. Its legs will become quite stumpy after a couple of days, and it will no longer be able to crawl.

9) Usually within four or five days, the caterpillar will shed its skin and form a pupa. In mid summer the pupa stage usually only lasts two to three weeks before the adult moth will emerge. Caterpillars found in the fall, however, will usually remain in a dormant stage, called diapause, over the winter months.

To be continued, when you write back and tell me you now have a pupa.

Email: Bill Oehlke

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