The giant swallowtail butterflies (Papilio cresphontes) that lay the eggs from which the orange dog caterpillars emerge are active throughout the citrus growing season. These caterpillars famously look like bird poop.
Q: I am finding orange dog caterpillars on my citrus now. Some are very small and some are almost two inches long. Why are they different sizes? Wouldn’t they all hatch at the same time?
A: The giant swallowtail butterflies (Papilio cresphontes) that lay the eggs from which the orange dog caterpillars emerge are active throughout the citrus growing season so the caterpillars you are seeing are likely from more than one egg laying event and did hatch at different times.
These caterpillars, which famously look like bird poop, molt through five instars or phenophases before they form a chrysalis or pupa, from thence into beauty. The rate at which they grow is related to the availability of food and the air temperature. Since your caterpillars are all on the same plants with the same conditions, it is safe to say they are all growing at the same rate.
If you’re curious like me, you can monitor their growth as a science experiment to see how long it takes for them to pupate. If the idea of sharing your observations with others in the interest of science gives you a thrill (also like me), there is a program on the Internet and an app for your smartphone called Nature’s Notebook.
There is a workshop on how use this application at Brandi Fenton Memorial Park from 9 a.m. to noon Friday, Sept. 25. Register at the Pima County website, ow.ly/Sd21w.
Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Questions may be emailed to plwarren@ cals.arizona.edu
