Foam…when we hear the word, we think of several things. The foaming waves crashing on the shore; the foam that forms at the mouth of a horse that has galloped at full speed; why, even the foam on top of a glass of chilled beer on a sunny afternoon!
In Nature, however, foam has a very different connotation; it is ofen a form of self-defence. There are creatures like the Frog Hopper, which, as it pupates, surrounds itself with foam, which looks exactly like a glob of human spittle and hence gives the creature both its name, and its defence against predators.
In snails, the production of foam or froth is an active form of self defence. Retracting into its shell might be a method of self-defence which is effective with larger predators, but it may not be a good idea with a smaller one. For example, an ant can crawl inside the shell. .In such instances, foaming may be helpful because the bubbly mess deters the small predator from entering the shell.
Sometimes, a foul-tasting substance also can result in snails starting to foam to protect themselves from contact with the unpleasant substance.
Bubbling can also be used as a defense mechanism in some life-threatening situations, by snails. Perhaps the most dramatic display of this is seen when gardeners purposely sprinkle salt on the snail as a form of pest control. The salt triggers a process known as osmosis where water is rapidly pulled out of the snail’s cells. Slime and air is pumped out to help the snail protect itself.
Some time ago, at the Valley School area, I found a snail under attack by a beetle,and documented the process of frothing/bubbling. At first, I could only see the snail, and was curious about it.
I then spotted the beetle trying to attack it, and documented the process of self-defence in a series of three short videos:
You can hear me and my friends speculating about the froth. The beetle seems to have given up, but here is the next video:
The beetle has removed the froth sticking to its legs, and has returned to the attack! Now, in the third video, the snail slowly tries to move away from the persistent beetle:
Some snails use bubbling for a different purpose, too. Some ocean-dwelling snails, which belong to the family Janthinidae, secrete mucus and trap air inside,creating bubbles that stick together. This foam forms a kind of raft, enabling the snails to come up from the sea bed. From bottom dwellers, they become surface surfers. This gives them access to a favorite food source, the floating jellyfish. So when we wipe the foam from a glass of beer as we wash down our meal, let’s think of the snails who use foam to secure their food!
