Believe It or Snot

The Definitive Field Guide to Earth's Slimy Creatures


By Nick Caruso

By Dani Rabaiotti

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From the scientist duo behind the New York Times bestselling sensation Does It Fart? and their excremental follow up True or Poo?, Believe It Or Snot explores the myriad variety of slime in the animal and plant kingdoms.

Your little brother isn’t the only nose-picking animal.

What is hyena butter and would it be appropriate to spread on toast? Why is giraffe saliva such a good lubricant? How does some mollusk mucus work like a fishing pole? And what’s the deal with pygmy sperm whales’ “anal syrup?”

In Believe It or Snot, scientists and bestselling authors Nick Caruso and Dani Rabaiotti detail the slimy secrets of 80 organisms that ooze, drip, dribble, and splatter. Not quite a solid but firmer than a liquid, slime is used by plants and animals for defense, respiration, movement, feeding, communication, and even reproduction. Slime, you might say, is the glue that holds our world together.

But that leaves an important question: which creature is earth’s slimiest?

In this book, the authors dive into the goo and come up with a definitive ranking of earth’s slimiest creatures-while offering up a plethora of facts about the natural world’s ooze, gunge, sludge, gunk, and goop.


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Gunge, goo, ooze, sludge, gunk, goop, slime: no doubt at some point in your life you have come into contact with one or another of these slippery substances. But what exactly is “slime”? The word slime can be applied to a whole host of substances that are slippery, gooey or even sticky. Essentially, slimes are viscous substances, which means they are somewhere in between a solid and a liquid. The more viscous something is, the more it holds itself in place and the less likely it is to flow. For example, water has very low viscosity, whereas custard has a much higher viscosity.

You might be most familiar with the slimy secretions made by your own body. Most of these are types of mucus—a slimy substance that does not dissolve in water, and contains specialized proteins called mucins that make the mucus thick and gel-like. One of the most obvious slimes produced by our bodies, and the substance in the title of this very book, is snot. So, what is snot? Simply put, it is the type of mucus found in your nose. It can be clear, or be yellow, or greenish when there is a high concentration of white blood cells or when it is especially thick. Snot is produced by the mucus cells that line your nasal passages, and helps protect the body against disease by trapping germs. It is made up of over 90% water, and not only does it contain mucins, but also special antibodies and bacteria-fighting proteins that help keep us disease free. Another form of human slime you may encounter on a daily basis is saliva—also known as spit, dribble or drool. This wet substance is produced by the salivary glands in the mouth, and has an even higher water content than snot, at 99.5%. The enzymes in our saliva help kickstart the process of digestion as we chew and swallow our food.

Snot and saliva are found throughout much of the earth’s biota (living organisms), but these aren’t the only substances that can make for a slimy or sticky situation. There are even some species that have their own unique slime composition, with proteins or other molecules not known to occur within any other species. Of course, these species aren’t out there producing slime for the fun of it: many species’ viscous secretions are not only useful but necessary to their existence—and the diversity of secretions is matched by the variety of their uses. You can learn a lot about the natural world through the slimes you find there: plants and animals have been found to use slime for defense, respiration, movement, feeding, sending chemical signals, reproduction, hibernation, and more! So, slime allows many species of animals and plants to thrive: it’s the glue that holds our world together…


A question that many people, including us, have been seeking the answer to since the dawn of time (or at least since work started on this book) is: which animal is the slimiest? To determine just how slimy each species or group of species is, we have used our expertise in the disgusting habits of living things to devise a specialist slime-ranking system. Read on to find out who will be crowned the slimiest organism of all…


Description: Produces very little to no slime


Description: Makes some slime, mostly internal


Description: Slime is involved with this creature’s daily life and can often be found on the outside of its body


Description: Touching this animal will likely leave you with a handful of slime


Description: Produces more slime than seems strictly necessary




Scientific name (Subfamily): Erinaceinae


Generally, if you see an animal frothing at the mouth, you should be pretty concerned, as it is often a symptom of disease. For the hedgehog, however, this behavior is perfectly normal, and potentially even encouraged. When exposed to strong scents, hedgehogs will chew up whatever the smell in question is coming from, while producing copious amounts of saliva, turning the smelly substance into a spitty, frothy mixture. They then spread this stinky, goopy, foamy substance across their spines, a behavior known as self-anointing. This process is repeated until much of the hedgehog is covered in smelly froth. This charming behavior has been observed with the exposure of hedgehogs to many substances, including (but not limited to) dog poo, glue, hyacinths, cigar smoke, perfume, soap, rotting meat, fox fur, and toad skin.

There are two theories as to why hedgehogs cover themselves in slobber. One is to mask their scent and protect them from predators. The other theory comes from the fact that hedgehogs are immune to many poisons, and have been observed to self-anoint using the toxins found in toads. It is thought that hedgehogs may do this to make their spines more painful to potential predators—an extra defense keeping them safe from harm. As if you needed another reason not to touch a hedgehog.


Scientific name (Genus): Chaetopterus


We’ll cover antibacterial slime (corals, here), hormonal slime (snails, here), toxic slime (fish, here) and suffocating slime (hagfish, here) but one species has slime with a rather different characteristic—it glows in the dark. Parchment worms, in the genus Chaetopterus, are a type of marine polychaete worm (page 57) named after the parchment-like tubes they build and inhabit. These worms are pretty mucusy—using their slime for feeding by ejecting mucus filters from the top of their tube (similar to larvaceans, page 31) and creating a current through their parchment tube, drawing plankton and other detritus into their mucus net and consuming it.

This is far from their coolest use of parchment worm mucus though. Natural light doesn’t reach the deep sea, so bioluminescence (glowing in the dark) is important for communication, attracting prey, and more. Should a predator or intruder disturb the chimney of a deep sea parchment worm such as Chaetopterus variopedatus, it will emit a cloud of glowing mucus, covering the intruder and making it obvious to predators. What’s amazing about the evolution of this trait is that parchment worms don’t have eyes, so can’t actually see the glow of their own mucus.


Scientific name (Species): Ulmus rubra


Plants produce a variety of compounds as a defense against herbivores, or to suppress the growth of other plants nearby, which would otherwise compete for resources. Humans in turn have found an array of uses for these different compounds, such as in medicine, though not all uses are noble-minded. One plant that produces such compounds is the slippery elm, which derives its common name from its mucilaginous inner bark, and occurs naturally throughout the eastern United States and southern Canada. One of the main uses for the slippery elm’s inner bark is as a demulcent, which pro-vides soothing relief to mucus membranes, such as for a cough.

A more devious use of slippery elm was by baseball players in the early 1900s. Pitchers would chew tablets made from its inner bark to produce more slimy spit for their “spitballs,” which would cause the ball to move unpredictably. Of course, the use of these tablets and the spitball pitch are now illegal in professional baseball, although that hasn’t stopped some pitchers from trying.


Scientific name (Domain): Bacteria (among others)


Biofilms are created when microorganisms, which require the aid of a microscope to be seen, stick to a surface, and then each other, through the production of slimy molecules known as Extracellular Polymeric Substances (EPS). Although biofilms are commonly associated with bacteria, other microorganisms like fungi and protists also produce these structures. For example, the dental plaque that can be found on our teeth (hopefully not much if you brush your teeth twice a day!), is a biofilm that is produced by several species of bacteria and fungi.

Biofilms can be pretty sticky too: in fact, they can attach to any surface, as long as that surface has at least some water. Within a biofilm, microorganisms can take advantage of a greater diversity of microhabitats, a higher concentration of food sources, and increased protection compared to the surrounding environment. Unfortunately, biofilms can cause problems for other species: dental plaque can cause gum disease, some biofilms provide bacteria with an increased resistance to antibiotics, and bacteria can use biofilms to colonize medical devices that can lead to harmful infectious diseases. But it isn’t all bad: biofilms can be found naturally on and near roots, providing plants with necessary nutrients; and humans even use biofilms as natural filters to treat wastewater and clean up hazardous chemicals.


Scientific name (Family): Sirenidae


Sirens are a family of aquatic salamanders found in the south-eastern United States and northern Mexico. These unusual species lack hindlimbs, have small forelimbs relative to their body, and are the only salamanders that regularly consume plant material, although they also eat aquatic invertebrates, fish, or pretty much anything else they can catch that will fit into their mouth. Sirens also possess external gills, a trait typically found only in larval salamanders, which means they need to be in water to breathe. But like other salamanders (slimy salamander, here), sirens can produce a slimy coating over their body to facilitate escape from predators. We can certainly vouch for its effectiveness: sirens are tough to hold!

Sirens can often be found in temporary wetlands and have a fantastically slimy adaptation to this ephemeral lifestyle. Sirens will burrow into the mud and form a slimy, mucus cocoon around their body, similar to the lungfish (here), which resembles parchment when dry. Although sirens don’t feed, and therefore lose body mass, while within their protective cocoon, they reduce their overall activity levels (known as aestivation) and can remain in this state for long periods of time—in laboratory conditions, one individual aestivated for over five years!


Scientific name (Species): Janthina janthina


Like the giant African land snail (here) and the Antarctic limpet (here), the violet snail uses its mucus to stay in one place: but it doesn’t attach itself to anything as solid as a rock or a house. Instead it stays at the surface of the open ocean. The violet snail accomplishes this feat by folding its mucus over air bubbles, forming a raft that is similar to bubble wrap. Of course, the ocean is constantly moving, as is the violet snail, because it drifts along with the current. If we were to use a raft we would sit on top of it, but the violet snail hangs below it, just beneath the ocean’s surface.

This floating lifestyle has its challenges: if their bubble raft pops, the violet snail will sink to the bottom of the ocean and die. Individuals don’t have a means to escape predators such as fish or birds, or to move around to meet a mate—instead males have to release sperm into the water in the hope that a female will come in contact with it in order to reproduce. They also can’t search for food—their food has to come to them. Fortunately, food sources are relatively abundant, and these little snails will happily scrape chunks off of other organisms floating by, like Portuguese men-of-war, for meals on the go.


Scientific name (Family): Didelphidae


Opossums are pretty weird, possessing some rather impressive anatomical oddities. First, they’re marsupials, which means their young develop within the female’s specialized pouch. But that’s not all—females have two parallel reproductive tracts and males have bifurcated (two-pronged) genitalia to match. This unusual reproductive system led to the (wildly) incorrect belief that male opossums mated with the female’s nostrils and she gave birth by sneezing into her pouch.

Although weird, none of this makes the opossum particularly slimy. However, they are periodically slimy—when they play dead. When threatened, opossums will fall to the ground with their mouth open, teeth exposed. Accompanying this award-winning acting is some slime from both ends. These marsupials will produce excessive saliva, to the point where it looks like they are foaming at the mouth, and will also produce a noxious-smelling green fluid from their anal glands. While it may be amusing to see this display (depending on your sense of humor), if you come across a wild opossum it is best to leave it alone, as their display is an involuntary fear response that can last for up to four hours, leaving them vulnerable and unnecessarily stressed.


Scientific name (Class): Anthozoa


What do coral and fish (here) have in common? (Aside from being found in the sea; hopefully you got that one!) What many people don’t know is they are both coated in mucus. Mucus is really important for protecting corals as they are sedentary and can be exposed at low tides in shallower waters. Should this happen, many corals produce extra mucus, which coats them and stops them from drying out. It also prevents other organisms from growing on the coral and protects them from the sunlight, as too much UV light is damaging. Too much sunlight can cause the algae that help keep corals alive to abandon them—this is known as coral bleaching. Coral rely on the algae that live in their zooxanthellae (the individual organisms that make up a coral) to provide them with energy through photosynthesis.

Coral mucus is also important for feeding, as it encourages the growth of bacteria, which are moved with their mucus by cilia into one of the organism’s many mouths, allowing the coral to digest the bacteria. Interestingly, there is also scientific evidence that the mucus creates an environment that stops bad bacteria, that would harm the coral from growing.


  • "Believe It or Snot serves up oozing helpings of helpful facts about Earth's slimiest organisms."

On Sale
Oct 22, 2019
Page Count
160 pages
Hachette Books

Nick Caruso

About the Author

Nick Caruso is a postdoctoral associate in the Department of Fish and Wildlife Conservation at Virginia Tech.

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Dani Rabaiotti

About the Author

Dani Rabaiotti is a PhD candidate and a zoologist at the Zoological Society of London.

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