Thursday, May 29, 2014 • 6:35 AM Comments ()

Spittlebugs

posted by Caleb Rounds

I’ve happened upon an insect I haven’t see in a while: a spittle bug. I found several of the offending loogis along the stem of a newly planted sage. The “spittle” is actually repurposed plant phloem. “Repurposed” in this case means sucked out of the plant and blown out an insect’s rear-end. The insect in question is a nymph froghopper or Philaenus spumarius. The spittle protects the fragile young bug from fluctuations in temperature and keeps it nice and moist. I use the term “bug” carefully, but these are in fact “true bugs” of the hemipteran order.

Despite the revulsion I feel when it looks like someone spit on my plant, there are seldom enough spittlebugs to cause real damage.

The Brits apparently call spittle-bugs cuckoo spit. It’s hard to imagine any sensible derivation for the name, but the Brits are the ones who failed to leave for the new world then elected Maggie Thatcher, so it’s not surprising that they’re just babbling (I admit I’m glossing over a bit of history there).

As adults, spittle bugs are called froghoppers, by most English speakers. Several sources I’ve seen mention that when looked at head on, Philaenus spumarius looks like a little frog. They also hop, hence “froghopper.”

I don’t believe I’ve ever seen an adult froghopper, though it’s quite possible I never noticed: they’re brown, don’t bother plants much and jump forcefully when disturbed. Froghoppers are the reigning champion insect jumpers. The research demonstrating this was performed by, Malcom Burrows, a professor at the University of Cambridge. In his initial spittlebug publication in Nature (Burrows, 2003) Burrows refers to them as froghoppers or spittlebugs and says nothing of cuckoo spit, he’s one of the good ones.

Froghoppers are the reigning champions because they jump farther, faster and harder than crickets and fleas. When preparing to jump, a froghopper extends its front legs and lowers its hindquarters (the opposite of what a cat does – they also don’t waggle their butt around). The upper portion of the insect’s rear leg (called a femur oddly) locks into a little pocket on the underside of its body (a protrusion from the coxa)– much as a catapult’s arm is locked in place. The muscles in the thorax then build up force, straining against this locking mechanism. When the force gets high enough the lock releases and the insect is thrown up and forward like a suicidal catapult.

Its initial acceleration can be as high as 4 m/s which means an acceleration of 408 g, what is commonly called g-force. Practically this means by the time you notice a froghopper, it’s 12 feet away from you. The force they must generate for this is 414 times their bodyweight. Humans usually manage about 3 times our body weight for a jump.

Of course animals can’t take advantage of this sort of jumping mechanism because we don’t have an exoskeleton so can’t lock our femurs into place against our body. We also don’t usually cover our babies in spit, though if it would have quieted a certain baby I know down, I would have tried.

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