Thursday, June 4, 2015

Spittle Bugs

Home sweet home.
Spittlebugs are all over the grass and shrubs in our riparian plantings.  Most people have seen the signs of them but few have bothered to search out the bug, a somewhat messy endeavor.  I will save you the time and the mess.

"No spit!  I feel naked."

Spittlebugs that we find are actually the nymphs of froghoppers, in the order Hemiptera, a diverse group that includes shield bugs, planthoppers, leaf hoppers, aphids and cicadas.  Froghoppers leap from plant to plant with amazing agility, with some jumping over 2 feet straight up.  They resemble treehoppers with minor differences that only an entomologist or another froghopper would notice.

Prosapia bicincta Kaldari.jpg
Two-lined spittlebug - Wikimedia- Kaldari
Many adult froghoppers can "bleed" from their tarsi (distal legs), exuding a hemolymph that is distasteful.  It is likely that their bright color as seen above send that warning message to predators considering a snack.

Meanwhile back to the nymphs who are covered with froth like you might find on top of a fine ale.  You don't want to know where it comes from, but here we go.  The nymphs always feed head down, an important skill if you want to cover your body from the end that is up.  They feed on sap which they pump through their intestine and out the anus at a rapid rate.  It is said to have an acrid taste, protecting them from predators.  As far as I know, the scientist who reported this has never admitted to tasting it.

Feeding head down on the stalk
Now the froth.  It is thought to protect the nymphs from dehydration, heat and cold, and to hide them from predators.  In addition to housing several larvae, a glob of spittle may hold an inquiline species, another species that lives in there without contributing or harming the spittlebugs.


Stenotus binotatus
Stenotus binotatus
















Wiping spittle on one blade of grass below, I uncovered several spittlebugs and a common plant bug, Stenotus binotatus.  This is a European invasive species that feeds on grasses and can be a pest on wheat.  There are no reports of it in association with spittlebugs, so it may have just been passing through.

How to explain the bubbles?  Here is one possible explanation from Northernwoodlands.org.
"The bug feeds standing on its head and excretes excess fluid from its anus. This fluid runs down and coats the spittle bug’s body. Specialized glands mix in mucilaginous compounds that increase the viscosity of the fluid and also stabilize the bubbles.  The nymph sucks air into its abdominal breathing tube and then forces it out to blow bubbles while pumping its abdomen up and down. As bubbles form, it uses its legs to pull the froth over its body. Safe within this foamy bath, the nymph grows and molts a few times, finally emerging as an adult. "
I find it interesting that the larva is sucking up xylem, the fluid coming up from the roots, delivering minerals like nitrogen incorporated in amino acids. The fluid is more dilute and not as nutrient rich as the phloem (memory tip: phloem=food flowing down) that is coming down from the leaves with nutrients to feed the roots. The larva must process lots of fluid to obtain its nutrition, expelling it continually. Some evidence suggests that they preferentially feed on legumes and nitrogen fixing grasses. Certainly it means the nymph has to suck a lot of lymph to get its nutrition. No wonder it is pushing it all out quickly!

Certainly, the head down feeding is important in getting the foam to cover up the nymph.  However they get it to froth, it does serve to protect them.  I suspect that predators know they are all hiding in there but have heard the reports of the acrid taste. 

There are more details on their specialized mouth parts at this link, clicking on "Look Inside."

3 comments:

  1. Wow! Those are some colorful spittlebugs. Most of the ones that I find are simply green:) I love the two-lined spittlebug! Wonderful photos.

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  2. The British call the foam around a spittle bug "cuckoo spit."

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  3. The British call the foam around spittle bugs "cuckoo spit", a term which confused me when I first encountered it in a novel.

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