January 26, 2015
By Elizabeth Long By now most people familiar with the BioSCAN Project know that we spend a lot of time looking at flies, but it may come as a surprise that we are equally passionate about other insect groups that can also be used for our biodiversity research. One such group is the Order Lepidoptera, the much beloved butterflies and moths. They are not usually collected by way of Malaise traps (they get a bit soggy in the ethanol), so for this reason there’s not much information about butterfly diversity in Malaise trap based projects. When I first started to identify the BioSCAN samples, I didn’t know what to expect and I was pretty sure that we wouldn’t be finding any new species of butterflies, much less 30 new species (yes, sometimes I have phorid fly envy!) — collecting and naming butterflies has been popular for centuries.
The great joy of butterfly "hunting" in the field. Photo credit: Zach Smith Recently I found the closest thing to a new butterfly species that we’re likely to see. I opened up a jar and to my pleasant surprise I found a big, beautiful, yellow and black butterfly that I have always called the Giant Swallowtail, Papilio cresophontes. The Los Angeles area has a few different species of yellow and black swallowtails, but I am particularly intrigued by this one. The caterpillars, which are incredible mimics of bird droppings, feed on citrus leaves, so unlike a lot of butterfly species, these beautiful animals tend to benefit from human agricultural activities in Southern California. Giant Swallowtails have an interesting geographic distribution — Southern California, Arizona, New Mexico, eastward into Texas and sometimes as far north as the Great Lakes states. It just so happens that right around the time that I found this species in one of the trap samples, new research was published that suggests that the species in our area has incorrectly been identified as the same species that shows up in the Eastern US. Their main lines of evidence involve some detailed and intricate differences that are only visible if you catch the animals in question and dissect out the male genitalia, or if you take a DNA sample and do some gene sequencing. Luckily for the accomplished amateur, though, there are some slight differences in the wing patterns of the proposed new species that allow us to distinguish between the two. Let's examine the photo below:
Can you spot the differences? Photo credit: Elizabeth Long The most subtle distinction is the yellow and black patterning on the “neck” of the butterfly, but there are also a few other pattern marks that are more obvious if you know what to look for. Take a look at the arrow labeled “1” in the photograph of both the western and eastern types, pointing out a black spot on a yellow background in the forewing. You can see that the spot on the animal on the right is much smaller than the corresponding spot in the animal on the left. Next, look at arrow “2.” This arrow is pointing at the feature that gives this group of butterflies their common name- the swallowtail. The animal on the left has a thinner tail with less yellow than the animal on the right. Next have a look at arrow “3.” The hindwing margin on the animal on the left is plain black, while the animal on the right has yellow markings on the scalloped edges. The animal on the left comes from California, while the one on the right is from Florida. If you’re visiting the part of Texas where these two types of swallowtails overlap, you should try looking for these wing marks and see if you can tell them apart! If Lepidopterists do determine that these are two distinct species, then the name of these butterflies will need to be changed, which brings up an important point about the taxonomy of every major group on the planet: the more we learn about the biology of organisms, the more we have to revisit and sometimes revise our classification schemes. Chances are good that some people in the Lepidoptera community will agree with this change, but many, including myself, will have a hard time letting go of old habits when it comes to names. I may learn to call the Great Swallowtail by its new proposed name Heraclides rumiko when writing a paper, but honestly in my head I’ll probably always think of it as Papilio cresphontes, the name it had when I first learned to identify it. But regardless of what I call it, I’ll always get a smile on my face when I see this beautiful creature waft through the citrus trees in the museum’s Nature Garden.