From Mussels to Frogs, How Animals Can Make Natural Glue

Certain animals use sticky situations to their advantage.

Producing incredible water-proof glue to hold themselves in place.Photo byAlejandro Piñero Amerio on Unsplash

Humans have been making various forms of glue for more than 200,000 years; as long as we’ve used tools, we’ve needed to stick one bit onto another. (The earliest human-used glues were made from birch bark, heated and turned into tar.)

But other animals have made glues for far longer. From frogs to mussels to silkworms, animals have created incredibly effective compounds that they use for growth, everyday survival — and defense against predators.

Here’s how those glues work — and how they’re put to use.

Mussels: surviving the tides

Mussels and clams grow in turgid, active environments, surviving under the pressure of crashing waves. They need a strong glue to hold themselves in place, so they don’t get washed away or dashed to pieces against the rocks.

They make this glue in a complex, multi-stage process, a bit like the two-part epoxy that is sold at hardware stores. Neither component is sticky until they’re mixed — at which point they adhere, even in water.

Specifically, in the muscular foot of the mussel that protrudes, tiny channels let the cells release tiny interior bags of proteins and metal ions (iron and vanadium). These compounds mix in the water and harden into a solid glue, which adheres in just 2–3 minutes.

The complex material (at least 8 proteins are involved) probably won’t be mass produced for underwater cement, but it could pay off for surgical glues, which need to stay strong in wet conditions.

Frogs: using glue for defense

Most of the time, “sticky and gummy” is not usually associated with a delicious meal. Excluding salt water taffy enjoyers, most of us would prefer that our meal, especially if we want to swallow it in a few bites, not have any sticky glue on it.

Researchers at Vrije University Brussel led by Dr. Kim Roelants found that some frogs, such as tree frogs in Madagascar, have evolved to produce sticky glues as a defense mechanism, making themselves less appetizing for snakes and birds.

Unlike the sturdy proteins used in mussel glues, frog glues are made of a mix of floppy protein “noodles” and sticky sugars, which combine to form a sticky gelatinous slime.

These frogs produce the glue but don’t secrete it unless threatened. Since the glue is immediately sticky, it provides immediate (negative) feedback for a predator. It only takes one or two attempted bites before a predator realizes that these frogs are more trouble than they’re worth.

Silkworms: building sturdy cocoons

Silkworms are a type of moth that have been grown in captivity by humans for thousands of years, so that we could harvest the fine threads of silk they produce for their cocoons. We spin that raw silk into fibers that can be woven into silk cloth.

But the silk cocoons produced by silk moths aren’t just the fibroin proteins that make up the fibers themselves; there’s also a gummy protein called sericin that helps stick the fibers together for the animal’s cocoon. It’s largely removed through boiling of the cocoons after harvesting.

Sericin has other useful properties; it’s antimicrobial and has been used to help suture wounds together. It’s also added to some cosmetics, where it helps reduce water loss from the skin to reduce wrinkles.

Sericin is secreted by the silkworm larvae as they form the cocoon, coating the fibroin fibers as they emerge to help them stick together. We generate a lot of it as a byproduct of the silkmaking process, and much of it is discarded these days. But in the future, it may become a valuable commodity on its own.

The payoff of biological glues

There’s plenty of great reasons to study biological glues. While they may not prove to be as strong as man-made epoxies and cements, these biological glues may offer other advantages. They may be more water-resistant, less prone to trigger an immune response if used on wounds or for sutures, or offer innate antimicrobial properties.

Most of the glues made by living creatures are made of proteins, and aren’t easily mass produced. But we may be able to obtain these as byproducts of existing processes, like the production of silk, and find additional benefits from compounds that we currently throw away.

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Other creatures, from slugs to slime-spitting velvet worms, are also able to produce their own forms of natural “glue”. From hunting to daily survival to defense against predators, there are lots of situations where a bit of stickiness can come in handy.

Most of these glues are made of a complex mix of proteins, only mixed when they are secreted from the animal (to avoid hardening too soon, inside glands or the animal’s body). They’ve got a wide range of properties, and likely have more benefits waiting for us to discover.

Perhaps one day, “frog glue” or “mussel glue” will be a part of everyday medical kits!

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