SPITTLEBUG

We all are familiar with the ”spittle-like foam” in our garden plants. Have you ever wondered where does it come from? Some of us may think these as ”snow”. In reality these foamy eruptions are produced by a sap drinker spittlebug, the nymph stage of the froghopper (Cercopoidea: Homoptera)! The frothy spit is often known as Cuckoo spit, as the name indicates, call of Cuckoo, the sign of spring.

In reality spittle-like foam they secrete around themselves are not spittle! Spittlebugs produce this foam by adding bubbles of air into an anal exudate that consists primarily of excreted xylem fluid – byproduct while feeding on the sap of plants. This fluid is further modified by adding some proteins and sugars to result in the formation of stable bubbles. Bubbles are produced when the spittlebug extends the tip of its abdomen through the surface of the foam and takes atmospheric air into a groove on the ventral surface of its abdomen. Bubbles are produced by submerging the tip of the abdomen into the foamy liquid and contracting the abdomen. By quickly repeating this action, a spittlebug can completely cover its body in foam within 15-30 min. Also, they can produce an incredible amount of this excreta, 150 to 280 times their own body weight each day.

Before their final moult from nymph to adult, many spittlebug species create a single large bubble within the foam mass. Within this ’bubble chamber’, they moult into the adult froghopper, remaining concealed until their cuticle has hardened.The adaptive function of the spittle mass is still debated. It has been proposed that it could protect the nymph from predation, provide microclimate that buffers temperature, prevent growth of fungi, or even act as a neutraliser of toxic ammonia. Nevertheless of the mentioned benefits, living inside a mixture of liquid and gas is an unusual respiratory environment for any terrestrial insect.

Insects lack lungs. They can breathe through small tunnels from the exterior holes known as spiracles that allows the air to flow through tunnels into their bodies. These spiracles are assembled in a groove that runs to the tip of the abdomen. A study was carried out by Philip G. D. Mathew and team from University of British Columbia, and reported how ”they” manage to breathe in the nested bubbles. The primary goal of this study was to determine which of these strategies are used. Are they ’foam breathers’ or do they ’snorkel’?

Spittlebugs are observed under microscopes and recorded the oxygen use and carbon dioxide production under various conditions. The research team reported that ”they breathe by extending the tip of their abdomen out of the foam mass, thereby bringing atmospheric air into contact with their ventral grove and abdominal spiracles”. Even when they are scared they submerged deeper into the safety of foam and stopped breathing for 46.5 s, on average, and never longer than 70 s. They do not attempt the intake of oxygen from the air trapped within the foam mass to prolong their submergence. Thus it is concluded that they are not foam breathers and they use the tip of their abdomen apparently like a snorkel.