Froghoppers are “true bugs”—in the order Hemiptera and placed in the suborder Auchenorrhyncha. They’re also known as “spittlebugs” because the nymphs reside in a mass of foamed-up excretion (incorporating plant sap) which looks like spittle (see below). This foamy mass clearly protects the young insects.
First, the adult, which is what we’re concerned with here:
This profile shows you why they’re called “froghoppers”. Aren’t they cute?
This is why they’re known as spittlebugs:
I’ll try to be brief here, for the contents of a new paper about these creatures, which appears in Proc. Nat. Acad. Sci. USA (click on screenshot below) can be conveyed briefly. But do go to the website as you can see movies of these things jumping; I’ve given links to the movie. The paper is free with the legal Unpaywall app, the pdf is here, and the full reference is at bottom.
This study used the species Philaenus spumarius, and the question was how these bugs hop off of smooth plants.
There are several ways insects and other creatures adhere to smooth plant surfaces. Some use adhesive pads like the familiar gecko, others have rough “heel” pads that produce friction against the plant, and still others, like this one, have strong spines on their feet.
As the authors show in the case of P. spumarius, its spines are also the mechanism that it uses to jump (after all, they’re called “hoppers”). And they can jump fast, attaining a velocity of close to 5 meters per second incurring forces of 550 g (!). That mean they must get a firm grip on the substrate. They do this by pressing strong claws on their rear jumping legs into the plant surface, leaving dents in the plant.
The first two bits of the figure below show the tough spines on the first and second tarsal segment of the hind legs, spines that are hardened at the tips. The third photo shows that these tips contain zinc, which makes them extra hard (it’s possible using X-ray scanning to detect specific elements in a sample). “D” shows a close-up of the spines, and “E” shows that some of these spines are damaged, almost certainly when the insect jumps on plant surfaces. (“Distal” means towards the end of the leg: away from the body.)
Goetzke et al. first determined that froghoppers can’t take off properly from glass, as they slip, slide, and fall all over (see the movie here), but they can leap successfully from a surface of somewhat softer epoxy on a slide or from ivy plants (see a leap from epoxy here). They hypothesized that this was because the hind-leg spines couldn’t get a purchase on the glass (they even determined that the hardness of the spines was sufficient to deform or pierce the epoxy or the plant, but not the glass). They then conducted high-speed video filming of froghopper leaps, which were of sufficiently high resolution to see those spines digging into the surfaces.
Finally, they photographed the position of the hind legs right before a jump, and showed that not only was the leaf damaged by the jump, but the damage (as revealed by a dye) was right at the position of the first and second tarsal segment, where the spines are. (See a deformation of epoxy in this video.) Finally, there’s a video of a magnificent leap from an ivy leaf (notice how the jump involves a somersault).
Below is time-lapse series of a leaping froghopper, the methylene blue stain showing plant damage, and holes in the plant surface where the tarsi of the rear legs resided:
Leaping! Notice the rear legs digging into the plant surface as it jumps:
Methylene blue stain right where the rear legs resided on this very jump. (Ta2 and Ta1 were where the second and first tarsal segments were placed.)
And damage to the leaf:
Finally, the authors note that a related group of leafhoppers don’t have these spines, but jump using “several soft pad-like structures on their hind tarsi” that produce high friction during a jump. This means that at least one of these structures—spines or pads—evolved independently.
Why don’t all the leafhoppers use the same morphology when jumping? The authors speculate that the “spine” species have shorter legs than the “pad” species but accelerate nearly three times as rapidly, which would produce considerable wear and damage to pads. That, of course, raises the question of why the “spine” species didn’t evolve longer legs. But there are tradeoffs, evolutionary history, and so on.
The upshot: The authors found a unique method of insect jumping, which may be fairly widespread since only this one species has been examined in such detail. They speculate that this discovery may “provide biological inspiration for robotic grippers”, and perhaps that’s true, but remains to be seen. I was particularly impressed, however, by the sequestration of zinc in the spine tips, which implies a sophisticated evolutionary and metabolic pathway for hardening the spine tips.
Tomorrow: Once again: why do zebras have stripes? The answer is now clearer.
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Goetzke, H. H., J. G. Pattrick, and W. Federle. 2019. Froghoppers jump from smooth plant surfaces by piercing them with sharp spines. Proceedings of the National Academy of Sciences 116:3012-3017.
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This is fascinating to me. In addition to learning how these particular spittlebugs/froghoppers jump, I learned that the immature bugs leave and return to their spittle houses. I’d assumed that they remained in their protective foam throughout their development.
Once again: why do zebras have stripes? The answer is now clearer.
This made it onto BBC television news this morning, including an interview with a scientist from Bristol university. I was somewhat distracted from what he was saying by a horse wearing a zebra striped blanket 🙂
Alrighty! The subject of the various ‘hoppers, including froghoppers (with much attention to spittlebugs), treehoppers, and leafhoppers would be a good subject for one of the True Facts videos.
You have spittle, wild colors, bizarre ant mimicry and great camouflage, along with a surprising amount of parental care in many species.
Nice! On the subject of spines, you never covered “A nudibranch removes rival sperm with a disposable spiny penis” article 🙂
https://link.springer.com/article/10.1007/s10164-018-0562-z?wt_mc=alerts.TOCjournals&utm_source=toc&utm_medium=email&utm_campaign=toc_10164_37_1
Wow, this is just so cool. Very glad to have learned all this.
Just wait until Nike get their mitts on this paper
Track spikes evolved long before the humans who now use them!
I have seen this bug in both stages—its annoying spittle stage and its cute hopping stage—but I never connected the dots. Thanks for an interesting post.
I guess the zinc detected in the tips is not in the metallic state – rather in ionic, right? If this is the case, can one make the argument that zinc would actually make the spines harder?
Leaf damage. Wow. I am looking forward to the zebra stripes.
I wanted to hear more about the metal. A creature that had evolved metallic spines would be a great addition to my science fiction story. LOL.
Very interesting. I have never heard of a biological creature utilizing metal. Are there any other examples in nature?
I had a spittlebug infestation on a field of unmowed grass last year. It was really weird…just about every blade of grass had a nymph. I don’t think they did any harm to the garden or ornamental flora; I don’t know what the adults eat. We’ll see what this summer brings.
Exciting! I wonder, in what form is this zinc? My speculation: it cross-binds other atoms, like in zinc finger proteins.
Why hasn’t anyone mentioned Wolverine yet!
Yeah!
I may forget but Safari hasn’t on this iPado.
I’m impressed. They’d make good competition for circus fleas.
Zebras! I can hardly wait.
Over here in GB ,the foamy stuff is known as Cuckoo Spit .
Wow, way cool! I like spittlebugs, they’re cute. 550 g’s — I guess it helps to be a creature of very little brain 🙂
It’s been a real blessing for me.
The zinc part is fascinating. I doubt that it’s just Zn++ binding proteins, but suspect that Zn++ binding proteins of some sort are somehow involved in generating metallic zinc.
What comes to mind is deposition of calcium, and in at least one mollusc, and so presumably many/all, a protein rich in histidine and phosphoserine seems to be involved in deposition of calcium. At least that’s the suggestion from a paper I recall from long ago. The phosphoserine would sequester Ca++ ions, and then nucleophilic attack on the (calcium) phosphoserine residues by histidine residues would release highly insoluble calcium phosphate in an ordered array, leaving behind the spent protein with crosslinks called histidinoalanine residues in their place. Since the crosslinked protein is an end-product, new protein must be synthesized to repeat the process.
Histidines are also frequent Zn++ ligands, so somewhere in the example of proteins involved in calcium phosphate deposition may lie a model for zinc deposition.
Thinking more on this, there’s no reason the structures couldn’t be insoluble zinc salts. The two counterions most prevalant in physiological media are carbonate and phosphate, and it turns out that both ZnCO3 and Zinc phosphate are water-insoluble. Generation of zinc phosphate crystals could be imagined in a scenario analagous to hydroxyapatite (calcium phosphate) in the above example, perhaps with histidine residues initially serving as ligands to Zn++ ions and positioning them as counterions to phosphate released from phosphoserine residues. That would be a lot simpler than imagining some secnario involving reduction to metallic zinc. (It seems that Zn phosphate is an old-line dental cement, too.)