At Rainforest Expeditions, entomologist Aaron Pomerantz describes a weird caterpillar that he found on a guided tourist expedition to the Peruvian rainforest. It has this weird behavior . . .
His ID:
After a little research, I found that this caterpillar is in the moth family Geometridae and is in the genusNematocampa. Also referred to as ‘horned-spanworms’ or ‘filament bearers’, these peculiar caterpillars can be found in North America and the Neotropics.
Okay, why do you think they do this? Pomerantz floats three hypotheses (indentations are his words):
1. David Wagner, in his field guide ‘Caterpillars of Eastern North America,’ notes:
“It is difficult to imagine what the [Nematocampa] larva is mimicking, but the overall effect is not unlike a fallen brown flower with exerted stamens. Alarmed caterpillars shunt hemolymph into filaments, enlarging them by as much as twice their resting length.”
What Wagner seems to be proposing is that the larva movement is similar to the way flowers or other plant matter move in the wind: the behavior more effectively blends the caterpillar into its surroundings.
I don’t find that terribly plausible, for the movement is coordinated and sudden, and would be detected by a predator (after all, it’s the predator who sets it off!).
2. The tentacles extend when the caterpillar is alarmed so that an attacking predator (such as a bird) has a higher probability of snagging a tentacle, as opposed to the main body, so that the caterpillar may drop away and escape with its life (similar to how some lizards are able to lose their tails).
More plausible, although this would be better if the tentacles were colored or had other ornaments that would distract a predator away from the body.
3. The setae, or “hairs,” located at the tip of a long tentacle could be highly sensitive vibration detectors that are able to sense predacious birds or insects that make nearby sounds.
Not that plausible, as if there’s a nearby predator that sets it off, what good does it do to detect the predator by touch?
There’s another hypothesis, too, which is mine: the tentacles secrete or spray some noxious substance that deters predators. The problem with that is that I can’t see anything coming out of the tentacles. But it could be invisible, like moth pheromones.
And yet another: the tentacles could make the caterpillar look bigger, deterring predators.
Finally, maybe the caterpillar is mimicking some other noxious animal that we don’t know about.
Your guesses?
The natural world seems replete with sources for sci-fi movie creatures…
Your guess is as good (and better) than mine. Any of those you suggested seem plausible. I can’t think of anything else.
The function seems clear to me: “raising the roof” in response to music.
Well, similar to your last two, I would guess the sudden change unnerves or surprises the predator. Or just makes it look not-prey-like. If a predator has an instinct to eat tube-shaped things, looking generically spikey-shaped may confer an advantage.
I’m reminded of Jeff Corwin facing down cheetahs: when they charge, you don’t run. Running is what prey does; if you run, you look like prey. If you don’t run, their predator instinct gets confused. Maybe a similar thing is happening here: when some predator with caterpillar-eating instincts appears, any mechanism that makes you not look/act like a caterpillar could be a positive adaptation.
Yeah the quick motion is freaky and may make predators think twice about giving it a taste.
This is the creature that has haunted my nightmares. The tentacles are an adaptation, much like Fredy Kruger’s face, to keep me from sleeping.
Clearly, caterpillar is auditioning for America’s Got Talent.
I think it looks like it is mimicking a spider.
I thought that too and what is scary about spiders is their dirty, unpredictable movements so I wondered if this wasn’t so much mimicking a spider but mimicking what is freaky about a spider.
dirty?
Creative iPad spelling – their darty, unpredictable movements. I really should proof read.
That’s what I thought too. Does the sudden movement seem like a warning? (Woodlouse spider is bitey and found in the same range too. Not a good resemblance though, except for the ‘legs’.)
Also, I wonder if the white tips of the tentacles act like a decoy and distract predators away from the body. It sure looks like the caterpillar can detect vibrations. I read something similar for hairstreak butterflies.
If it were warding off predators with a noxious substance, it would help to find out if there was a weird smell like other caterpillars have. It wasn’t mentioned so maybe there wasn’t a strong smell, if any.
Woodlouse spiders do a threat display too.
My guess too. Coordinated filaments mimic a spider’s attack posture. Perhaps the caterpillar’s main predator (assuming it’s not a bird) avoids a local spider that the caterpillar has evolved to mimic.
Yes, or a long-legged beetle. The markings on its back near the base of the tentacles suggest beetle to me, although I’m not entirely sure why.
At around 33 it looks like a long-horned beetle to me. It even seems to have a couple of orange bands which could be aposematic.
Some beetles are known for spraying noxious chemicals.
The caterpillar’s color pattern help camouflage, and the coiled up tentacles probably help that a little bit by breaking up the insect’s outline. That sudden eruption of long, white-tipped tentacles would be startling for any predatory, perhaps just confusing enough to save a caterpillar’s life from time to time.
That idea of spraying a chemical may be a good one. I’ve been sprayed by Black Swallowtail larvae and they didn’t have any obvious nozzle or anything, and yet my fingers ended up smelling like essence of carrot.
Looks a bit like something infested with a fungus. Perhaps predators prefer to avoid such tainted meals?
I vote for this one.
That was my first thought.
But why would there be movement? If a caterpillar was mimicking a fungus attack, shouldn’t it play dead?
It doesn’t seem to be moving once the appendages are extended. My notion is that if it gets startled by something that it continues to recognize as a threat, it remains still and waits for it to go away.
Or, probably more likely, it’s something else entirely. Maybe it drops like a stone to the ground if something touches its extended tendrils, thwarting attempts to grab it. Would have been nice if they tried touching them in the video to see what happened.
Craaazyyyy tentacles ohhh my god ohhhhhhhhh!
I noticed at :41 it kind of looks like a mantis. Maybe it’s “trying” to make itself look like a predator bug?
I like the simpler explanation however that it simply looks bigger.
Of course, there’s one more explanation that I dare not mention, having to do with a center giant tentacled monster currently asleep in R’lyeh.
Great video and interesting critter in any case.
A Thing That Should Not Be?
One more thought:
If the tentacles are there to detect vibration as the narrator says, wouldn’t they be extended all the time?
I imagine it takes some effort to keep the tentacles extended via hydrostatic pressure. There’s some muscle squeezing a bladder somewhere in the larva’s back, and the moment that muscle relaxes, the tentacles retract.
Somebody please tell Miss Litella that the word is “tentacles” — and that she can stop searching for a salve to cure the caterpillar’s condition.
Geometrid larvae are the familiar ‘inchworms’. I think the tentacles are to resemble a threat display commonly used in spiders. There are contrasting colors in the caterpillar that may help.
Yes, I agree. Thanks for posting that link; that’s what I’ve been imagining.
Good illustration.
The coiling and uncoiling is interesting, a bit like some plant tendrils?
Maybe the little sucker is just happy to be here.
Perhaps it imitates a caterpillar that’s parasitized; I seem to remember that some parasites, to switch hosts, cause their present host to produce extensions that move to attract the would-be new host to ingest them. Maybe a predator of caterpillars has learned to avoid ones that look like that.
Something remotely close to that scenario that involved inchworms–see #6 here:
http://io9.com/12-real-parasites-that-control-the-lives-of-their-hosts-461313366
Unrelated: there’s a quick moment around 36 where the caterpillar looks surrounded by some exudate or silk or something, but I think that’s a photographic artifact.
It would be good to know which frequencies trigger the behaviour. Also: do the tentacles remind anyone of ants/other arthropods that are infected by Cordiceps? I believe infected ants may be a strong deterrent.
But, I have to admit that I do not think there is a species of ants that goes marching through the rainforest shouting “OMG, … cray-zeeee … tentacles!”
That’s the crux of the enigma.
LIke quite a few of the others when I first saw this my immediate thought was “spider mimic” what type I have no idea.
An evolutionary behavioral ecologist (i.e., naturalist) might set up hidden surveillance cameras (with sound recording) in the caterpillar’s natural habitat and record how caterpillars respond to real-world stimuli. As it is, without data, although hypotheses are rife, the significance of the response remains enigmatic. If it were possible to block the behavioral response in individual caterpillars, both fitness effects and adaptive significance (or not) could be estimated by comparing the ecological fates of normal caterpillars with those lacking the behavior. Alternatively, and more easily done but less conclusive, encounters could be staged between caterpillars and putative predators and parasites. Although the video shows response with regard to sound, it is possible that the relevant stimulus is actually surface vibration or aerial vibrations of flying insect enemies. We could ask how caterpillars respond to a bird singing, a lizard running along the branch, a predatory wasp or parasitic fly buzzing (or fanning) close by, etc.
With regard to the video setting, it seems unlikely that these little brown caterpillars are found loose on green leaf margins in the full light of day. It would be useful to see the caterpillar in its normal feeding and resting places.
I have the following take on some of the hypotheses:
1. The ‘tentacles’ may mimic legs of a spider or ‘feelers’ of a centipede as it might appear emerging from a bit of dead plant material. This deception might deter a predaceous wasp, mantid, or even a small bird. (This is just a restatement of Jerry’s last hypothesis). In support of this, at 15 sec into the video you can observe two orange spots between the bases of tentacle pairs that look almost like eyes.
2. If caterpillars are rare, the caterpillar movement in itself (with exposure of the “false eyes”) may be sufficiently unexpected and unique in the experience of many predators to elicit an avoidance/startle response. (I see that Diana MacPherson has anticipated this suggestion also.)
3. If tentacles pop-out fast when a wasp or fly (predator or parasite) buzzes close by, the movement could surprise (and perhaps strike) and frighten the enemy away.
My problem is trying to imagine (or hypothesize) anything that might attack a caterpillar that is noisy when it hunts. Birds and lizards in feeding mode would vibrate branches, not sing or grunt. My ‘vote’ is for defense against predaceous and parasitic flies and wasps. In any case, most of the hypotheses (except perhaps chemical defense) are not mutually exclusive, such that indentifying one function does not exclude the possibility that different kinds of advantage are obtained with other types of enemies.
I think it’s interesting that when the caterpillar moves to the leaf’s top service the tentacles are symmetrically bent so that they resemble some insect’s leg morphology. At the same time its body looks like of the 3 insect body divisions.