Bubbles in forest: …what are these?

 

Around this time of year, i.e. during the monsoon season in Kanagawa Prefecture, when we stroll in a forest, we often meet with bubbles in bushes or branches. If it is in downtown parks, it could be a joke made by kids with soaps. In deep mountains, such mischiefs are unlikely. What are these? Recently, I found at least two origins for them.

One I learned is that bubble, called in English “cuckoo spit,” is a nest for larva of froghopper. These kids (and their parents) eat their meal from xylem of a plant. They insert their hypodermic needle-like mouth to xylem and drink water and bit of amino-acid + minerals the root sends to the upper part of their body. After drinking such water, the larva of froghopper mixes in their body the nutrition-less H2O and their waste products, i.e. ammonium, amino acid and wax ester, and pees it. So, their urine is sticky ammonium soap that can coat the branches of plants. These babies of froghopper have a butt which has a snorkel-like pipe inside. When they are in the pond of their pee, they can still breathe by sticking out the tip of their butt. By doing so, the bug blows the soapy pee, which makes those bubbles. Normally, except for a very specialized species, the predators of kid froghoppers cannot come in the bubbly nest since they cannot breathe inside. The fizzy house is a haven for larvae. We can find so many soapy shrubs in the June forest … there are so many babies inside, I guess. Very luckily so far in Japan, we have not heard outbreak of meadow froghoppers which can bring Xylella fastidiosa inside the xylem. This virus quickly clogs the xylem and the infected vegetation cannot carry nutrition the root sucks from the ground. The plant is killed quickly by starvation. We at least have not had this problem so far …

Lots of bubbly cradles for froghoppers

And since 2020, we forest instructors of Kanagawa are welcomed by another bubble in Yadoriki Water Source Forest やどりき水源林. The foams in water source forest we found are far larger and more solid than that for froghoppers. It is made by real frog, named forest green tree frog. The bubble in Yadoriki is their frogspawn. Historically speaking, the report of finding frogspawn of tree frog is recent phenomenon in Kanagawa Prefecture. People say somebody have brought them in Tanzawa. IUCN defined the frog in LC category so that giving their breeding place in Yadoriki would have certain meaning for biodiversity promotion, I suppose. Adult forest green tree frogs spend their life in boughs of trees in deep forest, but during their mating season they congregate near water, mate, and leave their eggs on a tree branch or something that is above water. The eggs are protected by foams created by parents’ secretion cued by insemination. The eggs are protected by the solid foam during their gestation, and new-born tadpoles stay in the bubble for a while. When it rains, the babies drop down from the foamy cradle to the water below. They then spend their childhood in water until they transform into adult frogs.

Forest green tree frog

So, ideally the water below the bubbly crib of forest green tree frog would be large enough and does not have torrent. In Yadoriki forest such environment is in short supply. The place we forest instructors found with a tree frog bubble was above a concrete gutter with grating lid on a paved forestry road. “Uh-oh. These frogs have real difficulties to find a suitable mating place, I guess.” “Yeah.” “Look, there are another foam pasted on the concrete wall of gutter.” “Isn’t it frogspawn of Schlegel's green tree frog?” “Nah, I don’t think so. They prefer the place nearer to still water, say a shore of a pond, or underground.” “Here, the gutter is dry now. Forest green tree frog does not care much if their frogspawn is washed by water or not.” “Look, here is adult!” Sure enough, on that day around the frogspawns, we’ve found 3 frogs, two strolling the ground below the treetop bubble, and one trapped in a puddle of the gutter whose water level was too low to flow out to Yadoriki Stream. “Hmmmm, they had large suckers on their fingertips.” “Yes, those are the typical fingers for forest green tree frog!” “And they are large. The frogspawn must be that of forest green tree frog.”

Standard location for frogspawn of forest green tree frog

Er … maybe, it’s the situation like
“Ask, and it shall be given to you.”

It’s trapped inside the gutter …
By the way, this one has brown-mottled body.
The appearance of forest green tree frog varies regionally
 from pure green to the one like this.
 From where the ancestor of this came from …?

Apparently, they are struggling to find a suitable place for childcare in Yadoriki and decided to take a compromise. In the small pool where one adult was trapped there were several 2-3cm tadpoles swimming. As we could not find large enough adult aquatic insects in the puddle, the tadpoles are relatively safe with fewer predators, I guess. Yadoriki forest is a water source forest of Kanagawa Prefecture. It rains a lot. During the next rain, that semi-dry gutter will be filled with water and run down to Yadoriki Stream. Adult frog will escape from the trap, but tadpoles may be washed down to the current under open sky. Lots of predators will come … Fingers crossed for the survival of Lightly Concerned species.

An adult and a baby

Someday, trapped frog family could swim there …

Migratory Blue and white flycatcher
has come to Yadoriki water source forest.
 IUCN categorize them LC as forest green tree frog.
In Kanagawa Prefecture, they are defined as “Vulnerable.”
 It seems to me they eat insects but not amphibians
… aren’t they predators for tadpoles and frogs?

If you find environmental issues in Kanagawa Prefecture, please make a contact with Kanagawa Natural Environment Conservation Center 神奈川県自然環境保全センター

657 Nanasawa, Atsugi City, 243-0121
〒243－0121　厚木市七沢657
Phone: 046-248-0323

You can send an enquiry to them by clicking the bottom line of their homepage at http://www.pref.kanagawa.jp/div/1644/