For biologists, the apple snail offers a way to study development and regeneration, providing insight to understand aspects of our own biology, and may one day help identify opportunities to induce regenerative capabilities in humans.

Why study apple snails?

Apple snails have four visible tentacles they use to sense and explore their surroundings—two long ones and two shorter ones framing the mouth like a moustache. They also have both gills and a lung along with a fifth extendable appendage used as a snorkel to breathe when water oxygen concentrations are poor. Their reproduction ritual involves a female and male snail mating, after which the female snail stores the sperm until ready to fertilize and lay eggs.

To some researchers, the eyes of apple snails are particularly intriguing. Their camera-type eyes—lens, cornea, retina—are anatomically similar to our eyes, yet when amputated, they grow back completely within a month. Due to this remarkable feat, apple snails hold enormous potential for understanding the mechanisms underlying sensory organ regeneration and how humans may be able to do so in the future.

In addition, comparing the development and regenerative capabilities of apple snails to animals in other branches of the tree of life may help us understand how and why certain traits are conserved throughout evolution while new ones emerge.

Invasive and voracious

Apple snails are a highly diverse freshwater animal indigenous to tropical locations in Central and South America, Africa, and Asia, yet can now be found worldwide due to both accidental and/or intentional introduction. As an exceptionally good source of protein—over 12 grams per 100 grams of snail meat with a mere 0.4 grams of fat—they are also voracious and invasive.

In 1980, golden apple snails were deliberately introduced to Taiwanese farms to create an escargot industry. However, this had unintended and catastrophic consequences: Apple snails’ insatiable appetites wreaked havoc on Taiwan’s rice industry and natural wetlands. Golden apple snails quickly spread to Thailand, Cambodia, Indonesia, Hong Kong, Japan, and China. Hawaii suffered similar agricultural difficulties to rice and taro production after an accidental golden apple snail infestation.

Apple snails at the Stowers Institute

Sealed tightly in a single room, nearly 1,000 golden apple snails are housed at the Stowers Institute in multiple tanks separated by age or size. The bubbling backdrop of their freshwater filtration system and the tendency for the snails to crawl up the sides of the tanks before suddenly plunging back to the bottom brings to mind a lava lamp brimming with tentacles.

The Institute established the golden apple snail as a novel unordinary research organism to study mechanisms underpinning the development of camera-type eyes and adult eye regeneration. They are also quite spoiled—fresh romaine lettuce three times per week and occasionally some kale. Apple snails do not have traditional teeth but do have a prominent tongue studded with tiny teeth to grind up their fibrous meals. And while not predatory, apple snails will resort to cannibalism provided that their snail mate has died.

Ongoing research is shedding light on apple snail eye evolution. From a morphological standpoint, the apple snail eye has most of the components of vertebrate eyes as well as cells common to invertebrate eyes like those of fruit flies. However, molecular pathways involved in eye development are remarkably conserved from fruit flies to apple snails to humans. Thus, their evolution likely combines conservation of some traits with the generation of new ones.

Enabling exploration

While few labs have studied the cellular and molecular biology of the golden apple snail to date, the development of molecular and genetic tools, experimental techniques, and housing systems over the last several years at the Stowers Institute has opened new possibilities. Enabling apple snail research is an example of the Institute’s ability to establish new, untraditional research organisms, and provide a foundation for other labs to study their unique characteristics, further deepening our understanding of biology.

Ultimately, by studying unordinary organisms, we may be able to answer fundamental biological questions that have remained elusive. The now genetically tractable apple snail may yield answers to how some animals can regenerate sensory organs, and why humans cannot.

Learn more about the Apple Snail