Montana Public Radio

Spit Bugs and Soapsuds: The Safety Of Tiny Bubbles

Jul 27, 2020

If you take a walk through fields this time of year, you can't help but notice what looks like gobs of frothy white spit on the stems of grasses and weeds. If you brush away the spit, you'll find a bright green froghopper or spit bug with shiny black eyes.

In a few weeks it'll have wings and hind legs that can propel it great distances - hence the name frog hopper. But at this stage of its life, all it can do is crawl. And since its body is soft and subject to drying out, it needs a way to protect itself from enemies and the sun. It does so with spit. But the spit doesn't come from the bug's mouth. 

Spittlebug nympth and adult
Credit Missoula Insectarium

As a spit bug sucks the sap from a plant, its body absorbs the nutrients and adds a chemical that makes it soapy. This liquid trickles out of its tail and forms a pool. Now the spit bug begins to make bubbles. Only instead of blowing through a straw as into a bowl of soapy water, it uses a row of plates on its underside that open when the bug raises its tail and close when it's lowered, much like a bellows we might use to fan a fire. The air forced into the liquid by this movement bubbles and froths and the spit bug is soon covered by a mass of foam. It takes a spit bug about fifteen minutes to build a new home when it's removed from its old one. The bubbles will last up to a week, no matter how hot or rainy it is. And an added advantage is that the froth is sticky so it can trap predatory insects that might otherwise make a meal of the spit bug.

By mid-July, spit bugs begin to change color to brown or gray, and their bodies harden and wings develop. At this point, they leave their bubble homes and begin searching for mates so that another generation of spit bugs will be around next year.

"Field Notes" is produced by the Montana Natural History Center.

(Broadcast: "Field Notes,"  7/21/20 and 7/24/20. Listen weekly on the radio Tuesdays and Fridays at 4:54 p.m., or via podcast.)