Whistle While You Eat

Forget your trouble
Try to be
Just like the cheerful chickadee
And whistle while you work

~Alternative lyrics to the Disney song from Snow White and the Seven Dwarfs

Walnut sphinx  caterpillar 1

A brief post today to share a remarkable scientific study on an unusual caterpillar behavior. In an earlier blog, I mentioned the unique sound-producing capabilities of the beautiful walnut sphinx caterpillar. What I had read is that the sound was produced to startle would-be predators. New research has refined this explanation. As reported in The Scientist (check it out to hear the caterpillar), a new study has shown the loud sound, created by the forcible expulsion of air from specialized holes along the side of the larva, is now believed to mimic the alarm call of birds. Some birds, such as black-capped chickadees, make special vocalizations when they see a potential predator. Other birds react by diving for cover. When this caterpillar is threatened, it emits a similar sound that can fool a hungry bird into thinking there is danger nearby, thus breaking off the birds’ attack on the larva. Amazing!

Heads or Tails?

There will always be scary predator eyes looking out at us from the bushes – it’s just that most of the time they are mounted on the rear end of a happily munching caterpillar.

~The Caterpillar Lab, Sam Jaffe, Director

On a walk at Yates Mill Park the other day, I came across one of my favorite caterpillars. My first glimpse was of a darkened blob on a leaf as I walked past a fence. The leaf was on a climbing vine of a Greenbriar, Smilax rotundifolia.

Turbulent Phosphila on leaf

Turbulent Phosphila larvae on Greenbriar leaf (click photos to enlarge)

When I stepped closer, I knew what the blob was…a group of tightly packed caterpillars! These striking larvae go by the unusual name of Turbulent Phosphila, Phosphila turbulenta. I discussed this species in an earlier post and am always delighted to find them. The name intrigues me…I understand the turbulent (characterized by conflict, disorder, or confusion) part…they are gregarious feeders in their early stages and can appear quite confusing when seen in a mass on the underside of a Smilax leaf (their only host plant). Sam Jaffe, an incredible photographer and educator on the subject of caterpillars, described them as looking like a mass appearing more like some strange outdoor QR code than biological life. Well said, Sam. It is the Phosphila part that has me baffled. If you break it down into its Greek roots, it means “phos” = Light, and “phila” = loving….light loving.

Turbulent Phosphila on stem 1

Turbulent Phosphila on Greenbriar stem

These guys usually hide on the underside of leaves as larvae or are clustered along a stem, hardly the behavior of a light-lover. Perhaps the adult moth is especially attracted to light? I don’t know. Perhaps the bright white spots on the rear of the caterpillar resemble bright points of light to someone? Not sure. Those spots are believed to function as fake eyes, and are more prominent and numerous than the eye spots on the anterior end of this species, making it tough to tell which end is which.

Turbulent Phosphila on stem

Turbulent Phosphila larvae, head downward, on Greenbriar stem

Whether the fake eye spots on the rear create a distraction for would-be predators away from the more vital head portion of the caterpillar, or they just serve as a startle and potential threat factor when seen in a grouping, the impact is one of confusion when you first look at these larvae. David Wagner, in his excellent reference, Caterpillars of Eastern North America, states that both the coloration and behavior suggest that these caterpillars are chemically protected. Whatever the case, they provide me with a wonderful visual treat every time I encounter them.

Poop, Pose, and Pastry

Reality is easy. It’s deception that’s the hard work.

~ Lauryn Hill

Nature is full of deception. And now it is being touted by none other than the New York Times.  A recent article on caterpillar defenses caught my eye. Researchers studied the late stage larvae of the Canadian Swallowtail (Papilio canadensis). The larvae are plump, green caterpillars with distinctive eye spots that are said to make them snake mimics. This type of mimicry is fairly common in the caterpillar world and is thought to provide some protection from avian predators. When I looked at the photos in the article, they looked very similar to something I found in the yard a couple of weeks ago.

Eastern Tiger Swallowtail larva third instar

Eastern Tiger Swallowtail larva – bird poop mimic (click photos to enlarge)

I posted a photo of the third instar larva of an Eastern Tiger Swallowtail (Papilio glaucus) in an earlier post. Like the early instar larvae of many species of swallowtails, it is said to resemble a bird dropping. These so-called bird poop mimics usually have a dark base color and at least one conspicuous white splotch on their body (usually near the center). But, the last two instars of this species look very different.

Eastern Tiger Swallowtail larva late instar

Eastern Tiger Swallowtail larva in later stage

I checked on the swallowtail caterpillar in my yard a week after that first photo and it looked almost exactly like the snake mimic photo of the Canadian Swallowtail larva. Gone was the bird dropping costume and in its place was a light green body with fairly prominent fake eye spots, and a slightly swollen anterior portion, giving it the appearance of a snake’s head.
Eastern Tiger Swallowtail larva late instar swelling anterior po

The larva rears up in a “snake strike pose” when disturbed

When the caterpillar is disturbed (I blew on it and touched the leaf for the photo above), it arches its body making the eye spots become more visible and enlarging the “snake head” region. In the recent study reported in The New York Times, researchers studied the predator deterrent efficacy of this snake look-alike strategy by creating tasty plain green “pastry caterpillars”. When placed on twigs, birds readily ate them. They then added eye spots and snake-like heads, and the birds tended to avoid them. In fact, adding just eye spots caused about the same rate of avoidance. This caused them to wonder….If real caterpillars don’t gain extra protection from extra deception, then how could their disguise have evolved?

They decided to present their pastry larvae to day-old bird chicks who had never seen a snake, theorizing that birds may have an innate fear of snakes and snake-like objects. Here are the results…When the chicks were offered simple green cylinders, they grabbed them. But when eye spots were added, the chicks became wary. Consistent with earlier research, the scientists found that adding a snakelike head didn’t make the chicks any more fearful. Over the next two days, the scientists presented the chicks with pastry caterpillars five more times. By the end, the chicks had learned that cylinders with eye spots were, in fact, tasty snacks. That was not the case when the chicks were presented with pastry caterpillars with both eye spots and snakelike heads. Even at the end of the study, the chicks were still fairly wary of the more realistic mimics. They concluded that birds have evolved a fear of snakes and that just a few characteristics, like eye spots, can make them wary. But, birds and other animals, can learn to distinguish between similar-looking objects, which may have driven caterpillars to evolve more elaborate disguises in order to keep fooling the birds.
Eastern Tiger Swallowtail larva late instar with osmeterium

After more provocation, the caterpillar extrudes its osmeterium, which happens to resemble a snake’s tongue

And, if you are going to have a snake’s head, you may as well have a snake’s tongue. Turns out, all members of the family Papilionidae have a special glandular organ, called the osmeterium, that can be extruded from just behind their head capsule when they are threatened. The forked shape resembles the forked tongue of a snake, further reinforcing this disguise to any would-be bird doubters. The osmeterium also produces secretions with a distinctive and disagreeable odor. These secretions have been shown to repel many invertebrate predators such as ants and mantids, but are not believed as effective against most vertebrate predators.

So, it seems this group of caterpillars are quite adept at the art of deception. From bird poop to strike poses, they offer an array of distasteful, or possibly even dangerous-looking, meal options for foraging birds. I am always fascinated by this long, slow dance of predator and prey and how it plays out in terms of behavior and appearance.


Caterpillar Conundrum

Turbulent Phosphila 2

Turbulent Phosphila (click photos to enlarge)

I have been away a few days celebrating a major birthday (hard to believe it is that number) and returned to find a few caterpillars from BugFest still active (most were released the day after the event). I was particularly pleased to see the snappily-attired Turbulent Phosphila munching away on its host plant, Greenbrier (Smilax sp.). I remember the first time I found one of these pin-striped beauties I could not decide which end was which, a common caterpillar conundrum. A frequent defense strategy of many types of insects is to present a false head to would-be predators. This usually involves eye spots of some sort since we, and most vertebrate predators like birds, associate eyes with the head of an animal. By going after the head first, a bird is likely to immobilize its prey quickly and cut off any escape attempt.

Turbulent Phosphila 1

Turbulent Phosphila – which end is which?

A close look reveals the truth – the last three segments of the rear of the caterpillar are somewhat enlarged and have prominent white spots suggesting eyes. Ironically, the true head end of the larva also has false eye spots on the thorax. The true eyes, like those of most caterpillars, are diminutive and arranged in arcs on the side of the caterpillar’s true head capsule, which is tucked on the right side of the larva in the image above (note the presence of the short antennae and true legs on that end). Maybe it is no accident that referee shirts look like the bold patterns of this larva – many of us question where their eyes are as well.

Turbulent Phosphila

Turbulent Phosphila on Smilax sp.

David Wagner (Owlet Caterpillars of Eastern North America) states that “the bold coloration is suggestive that the insect is chemically protected, although it remains to be shown if the Turbulent Phosphila is in fact unpalatable, or if its patterning is largely a ruse”.

Turbulent phosphila

Grouping of Turbulent Phosphila larvae

Young caterpillars are gregarious feeders on various species of Greenbrier, but as they grow older, they become more solitary. Finding a group of them on the underside of a Greenbrier leaf or clumped on a vine is a caterpillar-lover’s (and perhaps graphic artist’s) delight. The moth has two generations per year throughout much of our region and can often be found as late as November in the coastal plain. Finding the Curve-lined Owlet caterpillar, and now these interesting larvae, on Greenbrier, gives me a reason to appreciate this often maligned vine.

Cool Cats

“Teaching a child not to step on a caterpillar is as valuable to the child as it is to the caterpillar.”        Bradley Millar

Caterpillars are cool. I have been fascinated by these diverse and sometimes outlandish creatures for decades and have found them to be one of the best gateways for introducing people to the wonders of nature. I have used them effectively in teaching teachers, students, and the general public in my thirty year career with state parks and the museum. Their often unusual shapes and behaviors make them instantly appealing, they are fun to raise, and almost everyone that witnesses the miracle of metamorphosis is changed in some way. Tomorrow is the annual special event at the museum, BugFest, where we get to showcase caterpillars (and lots of other types of interesting invertebrates) with thousands of visitors. Several staff plus a few volunteers like me have been out looking for caterpillars this past week to share at BugFest. We have found a good variety but I want to highlight three of my favorites.

Yellow-shouldered Slug 1

Yellow-shouldered Slug (click on photos to enlarge)

I posted on one of the more exotic slug caterpillars last week, the Saddleback. There are more than twenty species of slug caterpillars in our region, and there are some that do not have the stinging spines of the Saddleback. The Yellow-shouldered Slug is actually one of the more mundane of the group in appearance, but I always enjoy finding any of this peculiar clan. This species apparently has stinging spines in early instars (an instar is the stage between molts), but lacks them in the final one. Slug caterpillars tend to have more instars than most caterpillars – from 7 to 9, instead of the usual 5 of most species. Not sure where this one is in the process although it is still pretty small.

Black-etched Prominent 3

Black-etched Prominent

The Prominents are another interesting group. Several have greatly elongated anal prolegs which resemble two tails. This Black-etched Prominent was feeding on a willow when it was discovered due to the presence of chewed leaves.

Black-etched Prominent 5a

Black-etched Prominent feeding on willow leaf

They do have a remarkable camouflage that mimics the leaf color and shape, even to the detail of having a faux mid-vein-like stripe along their sides. But if pretending to be a leaf doesn’t fool a potential predator or parasite, this prominent has a couple of other defenses in its arsenal. The caterpillar can rapidly pump fluid into the two “tails” when it is agitated thereby greatly increasing their length. It quickly arches them over the body and whips the air with them which is probably especially effective against small flying parasitic wasps and flies.

Black-etched Prominent face

Black-etched Prominent “face”

If further alarmed, the caterpillar rears back and arches its head toward the intruder, revealing markings tat look like a large false head with dark eyes. It also opens and closes its mandibles in a threat display. Ultimately, this, and several other prominents, may result to chemical warfare. They can shoot an acid spray from a gland underneath the head region. I have not yet experienced this so am unsure if it deters something like a large mammal with a camera, but will let you know if and when.

Curved-lined Owlet as dead leaf mimic

Curve-lined Owlet as dead leaf mimic

Then there are the caterpillars that I have seen in David Wagner’s field guide, Caterpillar’s of Eastern North America, and wished I could see first hand because they are so beautiful or bizarre (yeah, it’s true, I do think about such things). The Curve-lined Owlet is one of those species. And then, on the same day as the encounter with the Bobcat I reported in the last post, my friend found one of these Owlets on its host plant, Greenbrier (or Catbrier, Smilax sp.). And bizarre it is.

Curved-lined Owlet dark green background

Curve-lined Owlet on Greenbrier tendril

This caterpillar is a dead leaf mimic. It is very slow in its movements and will gently quiver from side to side when disturbed, much as a dead leaf would do in a slight breeze. The unusual elongate projections coming off the dorsal side make sense when you see the caterpillar in its environment – the tendrils of its host plant, Greenbrier, have similar curves, and the rolled edges of dying leaves are similar in color and shape. After BugFest, I will return this and a couple of the other caterpillars found down east to their rightful home (either as larvae or pupae). Every effort is made to return the larvae to the proper environment after they are used for educational purposes. Now, if I could only find that one on page 270 that mimics the color and shape of a cluster of green grapes.

They Grow Up So Fast…

Bumblebee Moth egg

Snowberry Clearwing Moth egg

Question Mark egg 1

Question Mark egg

It seems like just yesterday they were just a gleam in their parents multifaceted eyes, and then, before you know it, they are off to pupation college. I reported on some egg-laying of butterflies and moths in recent posts and decided yesterday to go out and look for the young ones out in the garden. It has been about three weeks since I photographed the eggs. Most lepidopteran eggs hatch within 3-5 days after being laid and many species of butterflies and moths have larval stages that last about two to three weeks. So, I expected to find some caterpillars that were in the mid to late instar stage of development. I did find a couple, and while I can’t be sure they are the ones from the eggs I photographed, they probably are from eggs laid about the same time.

Snowberry Clearwing larva mid instar

Snowberry Clearwing larva

The species I nicknamed Little Spike (a Snowberry Clearwing Moth larva) has become more proportional to its caudal horn (tail spike) and changed color. I cannot find any reference as to the function of the tail spike found on most sphinx moth larvae, other than one tongue-in-cheek mention that it must be to scare gardeners. Indeed, there is a common misconception that these types of caterpillars can sting you with that horn (they cannot). Perhaps it is similar to the angled stripes that many species have along their sides and serves to help break up the typical caterpillar outline or shape by blending in with leaf veins, petioles, etc. Notice that this larva does exhibit a form of counter-shading, with the color becoming fainter as you move from the bottom to the dorsal side of the body. Since this species often feeds on the underside of the light-colored leaves of honeysuckle plants, this color scheme makes sense, especially when viewed from below the leaf, causing the caterpillar to blend in more with its surroundings.

Question Mark larva late instar

Question Mark larva late instar

Next I looked over the elm sapling where I had found the Question Mark or Eastern Comma eggs (they are identical). It turns out they were laid by a Question Mark. The caterpillar is a rather fierce-looking larva armed with branching spines (scolia). I had to check the field guide to make sure it is not one of the so-called stinging caterpillars (like Io Moth or Saddleback Caterpillars) whose stiff spines contain venom which can cause severe irritation when touched. This species is, indeed, harmless, but the spines undoubtedly serve to protect it from many invertebrate predators and perhaps deter others.

Question Mark larva late instar 1

Question Mark larva posture

This particular caterpillar also had an interesting behavior when disturbed. It arched its body in a tight curve and stuck out the posterior end. I have seen some caterpillar species do this that can exude distasteful chemicals from their anus, or that have fake heads on their backside. I’m not sure if this is a species level behavioral trait or what the function might be if it is, but anytime I am faced with an array of sharp spines, I think twice before grabbing.