A second sphinx moth: Xylophanes pluto

Last year I found an adult sphinx moth, Enyo lugubris, on our pool fence. It was the first sphinx moth I’d found on our new property, and it sure brightened up my morning.

The other evening, as I was fighting another skirmish in my never-ending war against the scale bugs on my firebush, I uncovered a moth caterpillar from a new (to me) sphinx moth species, Xylophanes pluto:

It’s one of the “hornworm” caterpillars, a name given to the larvae of the moth family Sphingidae for obvious reasons. If ever a lepidopteran larva looked like a unicorn, it would be the members of this family, although I must admit that the horn appears to be attached to the wrong end. These caterpillars can grow quite large; at only one inch long, this one is pretty small, which means that it must be a relatively early instar.

Apparently these caterpillars come in three color forms: green, brown, and purple-brown. This one is purple-brown, which seems to be perfect camouflage for the plant it was foraging on, since firebush has brown stems and reddish/purple berries, and even the green leaves have a reddish/purplish cast.

Amidships, the caterpillar has four prominent “legs”; these are actually known as the anterior prolegs, to distinguish them from the relatively tiny thoracic legs (you can just make them out on the ventral side of the body up above the eyespot, flying free, not touching the plant at all), while the anal proleg is pretty hard to distinguish; it’s on the end that’s scrunched up at the crotch of the plant, anchoring the beast as its front end wiggles in space.

According to W.J. Holland, while the genus Xylophanes is “very large, containing fifty species and many subspecies,” only two species are known within our territory,

though it is possible that a thorough exploration of southern Florida may show that one or two of the species which are found in the Antilles also occur in that State. The student will have no difficulty recognizing the species occurring within our borders by means of the figures which are given upon our plates.

Xylophanes pluto, Plate IV, Fig. 9, from Holland's Moth Book

The two species Holland mentions are X. pluto and X. tersa, and I’ve now seen them both! (Although only one of them has been in my back yard; witness the poor cellphone snap of X. tersa that is my only record.) Unfortunately, I will have great trouble recognizing this species because I’ve never seen the adult form; I’ve seen only two individuals of the larval form. They’re quite distinctive, but I hope to see the adult one of these days.

Etymology: xylo- is wood, -phanes is from Greek phainomai, to appear or come into view. Pluto, of course, is the Roman god of the underworld (the Greek god of the underworld is Hades). The genus was named by Hubner in 1819, although this particular species was described earlier, by Fabricius (1777).

After I first found this beast, I went out at different times of day and evening trying to find it again with no success. I wonder whether the ants that tend the scale bugs are responsible for its disappearance, or if it just crawled off searching for greener pastures? But a couple of weeks later, just as I was readying this post for publication, I found another individual, this one much more brown than purple, and right around lunchtime! It was nowhere near as active as the first one I found (since they’re nocturnal feeders, it’s not surprising that one found near noon would be sluggish).

Having seen the beautiful photos posted to bugguide.net by photographers like Alan Chin-Lee (another Boca resident), I took care to get some nicer angles. I particularly wanted to show both “eyespots”:

Here’s the side view showing the “horn” of this hornworm:

I’m hoping that my removal of as many scale bugs as I can find on these plants will encourage the survival of these sphinx moths; I’m fairly certain the first one was “cleaned” by the ant ranchers. I’ll keep checking on this one, but I won’t hold my breath, either.

References

Holland, W. J. (1903). The Moth Book: A Popular Guide to a Knowledge of the Moths of North America. NY: Dover. Repr. 1968 with new foreword by A.E. Brower.

Wagner, D. L. (2005). Caterpillars of Eastern North America: A Guide to Identification and Natural History. Princeton UP.