Ugliest Animal: Candidates and Adaptations

By Dr. Zubair Khalid, DVM, MS, PhD · 2026-09-20

There is no ugliest animal in biology. "Ugly" is a human aesthetic judgment, and the species most often nominated for the title are simply animals whose bodies are shaped by extreme environments rather than by human taste. The famous 2013 "world's ugliest animal" vote was a publicity contest run by the Ugly Animal Preservation Society, not a scientific ranking, and the winner, the blobfish, owes much of its slumped appearance to being photographed after being hauled from deep water into low pressure.

Understanding these animals means separating the photograph from the organism. Each candidate on the usual list, the blobfish, the aye-aye, the naked mole rat, the star-nosed mole, and the deep-sea anglerfish, carries anatomy that solves a specific survival problem. This guide walks through those problems and the adaptations that answer them.

What "Ugliest Animal" Actually Means

The phrase "ugliest animal" describes a reaction, not a category. Humans judge faces and bodies against the proportions we see in our own species and in familiar pets. Animals that live in darkness, in high pressure, or underground often evolve proportions that look wrong to us because the selection pressures that shaped them have nothing to do with being seen.

The 2013 contest made this explicit. It was designed to draw attention to threatened species that get less conservation funding than charismatic mammals, and it used a public vote as a marketing device. The result was a viral list, not a taxonomic finding. No professional body ranks animals by appearance, and no field guide uses ugliness as a trait.

A second problem is that the most shared images of these animals are often misleading. The blobfish is the clearest case. A fish built for crushing pressure at depth does not hold its shape when that pressure is removed, so a specimen brought to the surface in a net looks like a gelatinous lump. That lump is real tissue, but it is not the animal's living form.

The Blobfish: A Deep-Sea Fish Out of Its Element

The blobfish (Psychrolutes marcidus and related species) lives on the seafloor off southeastern Australia and New Zealand, typically at depths of several hundred to over a thousand meters. At those depths the water pressure is many times greater than at the surface, and the fish has no swim bladder, the gas-filled organ that most bony fish use to control buoyancy. A gas-filled bladder would collapse or expand violently with changing pressure, so the blobfish does without one.

Instead, its body is built from low-density, gelatinous tissue that is slightly less dense than seawater. This lets it hover just above the bottom without spending energy on swimming. The trade-off is that the same tissue has almost no structural stiffness. When the fish is pulled up quickly, the external pressure that was holding its shape disappears, and the body expands and sags.

That is why the viral photograph shows a pale, drooping face with a large "nose." In its habitat, the fish is a normal-looking deep-sea sculpin relative, with a firm outline supported by the surrounding water. The lesson is general: any deep-sea animal photographed at the surface is a decompressed version of itself, and its proportions in that image are not its proportions in life.

The Aye-Aye: Percussive Foraging and a Very Strange Hand

The aye-aye (Daubentonia madagascariensis) is a lemur from Madagascar that weighs about 2.5 kilograms and eats a diet that is over 88 percent invertebrates, mostly wood-boring larvae [1]. That combination, a relatively large primate living almost entirely on insects, breaks a common ecological rule that large animals cannot sustain themselves on such small, scattered prey. The aye-aye gets around the rule with specialized anatomy.

Tap-scanning with the middle digit

The aye-aye finds larvae by tapping on wood with its thin, elongated third digit and listening for the hollow sound of a tunnel beneath the bark. This behavior is called percussive foraging, or tap-scanning. The taps produce dominant frequencies between 6 and 15 kilohertz, and the aye-aye's hearing is tuned to that band [2]. Once it locates a tunnel, it uses its rodent-like incisors to gouge into the wood and its narrow finger to hook the larva out.

A chewing apparatus built for gouging

Gouging through wood takes force, and the aye-aye's jaw muscles reflect that demand. High-resolution imaging of the masticatory musculature shows that every jaw muscle in the aye-aye is absolutely and relatively larger in volume and physiological cross-sectional area than the equivalent muscle in a similarly sized generalist lemur, the mongoose lemur [3]. Dissection of an adult aye-aye confirmed very large jaw adductor muscles relative to body size [4]. The incisors are also hypselodont, meaning they grow continuously, which keeps them functional against constant wear from gnawing.

A second thumb

The aye-aye's hand has another feature that is rare among primates. Alongside its specialized third digit, it has a pseudothumb, an accessory digit built from an expanded radial sesamoid bone plus a dense cartilaginous extension called the prepollex [5]. The structure receives attachments from three muscles that can move it in several directions, and it has its own palm pad with independent dermatoglyphs, the skin ridges that form fingerprints. The best-known parallel is the giant panda's false thumb. In both cases the extra digit improves grip and dexterity in a hand whose normal first digit is not suited to the task.

Why the aye-aye looks odd to us

The aye-aye's large ears, long bony finger, and continuously growing front teeth read as unsettling to many people. Each of those features is a tool. The ears detect larvae. The finger taps and extracts. The incisors open the wood. The pseudothumb holds on. Nothing about the animal is decorative, and nothing about it is accidental.

The Naked Mole Rat: A Mammal That Breaks Several Rules

The naked mole rat (Heterocephalus glaber) is a small, nearly hairless rodent from eastern Africa that lives in underground colonies. It is the most studied of the "ugly" candidates because its physiology is genuinely unusual, and the research literature on it is deep.

Eusociality

The naked mole rat is one of only two known eusocial mammals, meaning it lives in a colony with a reproductive hierarchy similar to that of social insects [6]. A single queen is the only breeding female, and most colony members do not reproduce. The queen maintains an exceptionally large ovarian reserve throughout her life, and germ cells in this species continue to proliferate after birth, which contradicts the standard mammalian pattern of a fixed egg supply that declines with age [6].

Temperature biology

Naked mole rats are often described as poikilothermic-ish, meaning their body temperature is unusually variable and tracks the burrow environment more closely than in most mammals. They have low basal metabolic rates and rely heavily on glycolysis rather than oxidative phosphorylation to make ATP, the cell's energy currency [7]. That shift is part of how they tolerate the low-oxygen air deep in a crowded burrow.

Hypoxia tolerance

Burrows can become hypoxic, meaning low in oxygen, and hypercapnic, meaning high in carbon dioxide. Naked mole rats stay conscious and active in hypoxia while rapidly suppressing their metabolic rate, a combination most mammals cannot manage [8]. Their hearts show elevated glycogen stores, which supports glycolytic energy production during ischemia, and they show negligible tissue damage after ischemia-reperfusion injury compared with mice [9]. Their brain extracellular space actually expands under ischemic conditions and keeps diffusion working, rather than shrinking as it does in rats [10].

Cancer resistance and longevity

Naked mole rats are highly resistant to cancer and to many age-associated disorders, and they live about 37 years, far longer than a rodent of their size should [9]. One contributor is their hyaluronan, a very high molecular weight form of a glycosaminoglycan, a structural sugar chain in the extracellular matrix. Their tissues produce and process more of it and degrade less of it, which supports skin elasticity, faster wound healing, and resistance to cancer and arthritis through CD44 signaling and related pathways [11]. Genome work has also identified gene losses tied to their biology, including losses in sperm-related genes that may explain their unusual sperm and a loss related to the absence of natural killer cells [12]. Additional gene losses in both naked mole rats and blind mole rats cluster in functions such as the visual system and the DNA damage response, which fits a subterranean life [13].

What the naked mole rat is not

It is not a hairless mole. It is a rodent, not a mole, and its closest relatives among the African mole rats are the Damaraland and Cape mole rats. It is also not cold-blooded in the strict sense. It is a mammal with an unusually flexible thermal strategy, and the details are still being worked out.

The Star-Nosed Mole and the Anglerfish

Two more species appear on most informal lists.

The star-nosed mole (Condylura cristata) has a ring of fleshy tentacles around its nostrils. These are not decoration. They are densely packed with mechanoreceptors, sensory cells that detect touch, and they let the mole identify and eat prey faster than almost any other mammal. The mole is functionally blind and forages in mud and water, so touch does the work that sight would do elsewhere.

The deep-sea anglerfish is famous for the bioluminescent lure that dangles in front of its mouth and for the extreme size difference between males and females. The light comes from symbiotic bacteria housed in the lure, and it draws prey close in water where sunlight never reaches. In several species the tiny male attaches to the female and fuses to her body, becoming a permanent source of sperm. Both traits solve the same problem: finding a mate and finding food in a vast, dark, sparsely populated habitat.

Comparison Table: Species, Habitat, and Adaptive Function

Why These Features Look Strange to Us

Human faces are built around forward-facing eyes, a protruding nose, and a mouth with visible teeth. We read emotion and intention from those features automatically. When an animal has no eyes, or eyes in the wrong place, or a mouth that opens differently, our face-processing system flags it as wrong.

That reaction has no biological meaning. The star-nosed mole's tentacles are a better sensory organ than our fingertips. The aye-aye's finger is a better probe than our index finger. The naked mole rat's skin produces a matrix molecule that keeps it cancer-resistant. Judging these animals by human standards measures the wrong thing.

There is also a conservation angle. The 2013 contest existed because species that look unusual to us tend to attract less funding than pandas and tigers. That is a real problem in conservation biology, and it is the reason the contest was created. The solution is not to call these animals ugly. It is to explain what their features do.

Practical Implications for Researchers and Keepers

If you work with any of these species, the practical points are specific.

Blobfish and other deep-sea fish cannot be kept in standard surface aquaria. Their tissue is adapted to pressure, and a tank at atmospheric pressure does not reproduce their habitat. Museum specimens and photographs taken at the surface show a decompressed animal, so any morphological measurement taken from such a specimen needs to be interpreted with that in mind.

Aye-ayes are endangered and protected. In Madagascar they are studied through non-invasive methods such as feeding traces on wood, which serve as a proxy for larval abundance [14]. Captive care requires a diet and enclosure that support gouging and tap-scanning, because those behaviors are not optional for the animal's welfare.

Naked mole rats are now a recognized comparative model in aging research [15]. Colonies need stable temperature, controlled humidity, and burrow-like tunnels. Their unusual thermal biology means standard rodent housing assumptions about thermoregulation may not apply. Their immune system also differs from that of mice, with a myeloid-dominant composition and macrophages that behave differently under inflammatory stimulation, including reduced nitric oxide production [16].

For anyone keeping star-nosed moles, which is rare outside research settings, the enclosure must provide wet, soft substrate. The tentacles are the animal's primary sense organ, and dry or abrasive bedding damages their function.

Common Mistakes and Limitations

The first mistake is treating a viral photograph as an accurate portrait. The blobfish image that circulates online is a decompressed specimen. It is not what the animal looks like at depth.

The second mistake is assuming "ugly" means "poorly adapted." Every feature described here is a solution to a problem. The aye-aye's finger is not a defect. The naked mole rat's hairlessness is not a defect.

The third mistake is confusing the naked mole rat with a mole. It is a rodent, and its subterranean habits evolved separately from true moles.

The fourth mistake is overstating what is known. Naked mole rat cancer resistance is well documented, but the mechanisms are still being mapped, and no single gene explains it. The 2024 genome assembly identified gene losses and duplications tied to hypoxia tolerance, oxidative stress, and nervous system protection, and the work is ongoing [12]. Similarly, the search for the mechanism behind the naked mole rat's lack of glutamatergic channel arrest during hypoxia produced a negative result, which means the protective mechanism is something else [17]. Science on these animals is active, not settled.

The fifth mistake is treating the 2013 contest as a scientific result. It was a vote.

Finally, individual animals vary. Any specific health or husbandry question about a particular animal needs a veterinarian or a qualified biologist who can examine it directly.

Frequently Asked Questions

What is the ugliest animal in the world?

There is no scientific answer. The title comes from a 2013 publicity contest, and ugliness is a human judgment rather than a biological property.

Why does the blobfish look so different in photos?

The blobfish is a deep-sea fish with a gelatinous body and no swim bladder. When it is brought to the surface, the pressure that supported its shape is gone, so the tissue expands and sags.

What is the aye-aye's long finger for?

It uses the thin third digit to tap on wood and listen for hollow tunnels made by wood-boring larvae. This is called percussive foraging.

Are naked mole rats really cold-blooded?

Not in the strict sense. They are mammals with unusually variable body temperature and low metabolic rates, which is why they are sometimes described as poikilothermic-ish.

Why are naked mole rats resistant to cancer?

They produce a very high molecular weight form of hyaluronan in their tissues, which supports resistance to cancer and arthritis through CD44 signaling and related mechanisms [11].

Do naked mole rats live in colonies like ants?

Yes. They are one of only two known eusocial mammals, with a single breeding queen and non-reproductive colony members [6].

Is the star-nosed mole blind?

It has very poor vision and relies on the touch-sensitive tentacles around its snout to find and identify prey.

Was the 2013 ugliest animal vote scientific?

No. It was a public vote organized to draw attention to threatened species that receive less conservation funding than popular mammals.

Related Articles

• Faculty candidate presentation structure
• How to Use Your Reference List to Find Candidate Journals
• Laboratory Scientist Jobs in Australia: A Guide for International and Local Candidates
• Gastrointestinal Adaptations in Exotic Herbivores
• Environmental Adaptation: How Organisms Adjust and What It Means for Careers
• Equine Exercise Physiology: Cardiorespiratory Adaptations and Performance Assessment
• What Animal Lives the Longest? Records Explained

Sources

1. Re-assessing the applicability of the Jarman/Bell model and Kay's threshold to the insectivorous aye-aye (Daubentonia madagascariensis).
2. Receiver bias and the acoustic ecology of aye-ayes (Daubentonia madagascariensis).
3. DiceCT Analysis of the Extreme Gouging Adaptations Within the Masticatory Apparatus of the Aye-Aye (Daubentonia madagascariensis).
4. Anatomy and adaptations of the chewing muscles in Daubentonia (Lemuriformes).
5. A primate with a Panda's thumb: The anatomy of the pseudothumb of Daubentonia madagascariensis.
6. The Everlasting Ovary: Decoding the Mechanisms of Lifelong Oogenesis in the Naked Mole-Rat.
7. Naked mole-rat and Damaraland mole-rat exhibit lower respiration in mitochondria, cellular and organismal levels.
8. Adaptations to a hypoxic lifestyle in naked mole-rats.
9. Naked mole-rats have distinctive cardiometabolic and genetic adaptations to their underground low-oxygen lifestyles.
10. Brain extracellular space of the naked mole-rat expands and maintains normal diffusion under ischemic conditions.
11. Naked mole-rat hyaluronan.
12. An updated reference genome sequence and annotation reveals gene losses and gains underlying naked mole-rat biology.
13. Gene losses may contribute to subterranean adaptations in naked mole-rat and blind mole-rat.
14. Resource preference of an adult female aye-aye (Daubentonia madagascariensis) in Madagascar's Ihofa Forest.
15. The Untapped Potential of Comparative Biology in Aging Research: Insights From the Extraordinary-Long-Lived Naked Mole-Rat.
16. Macrophages from naked mole-rat possess distinct immunometabolic signatures upon polarization.
17. Absence of a glutamatergic channel arrest mechanisms in hypoxic naked mole-rat cortex.