These are our favorite animal stories of 2023

a Caribbean box jellyfish

Even without a brain, the tiny Caribbean box jellyfish can learn to avoid obstacles, research revealed in 2023.

J. Bielecki

From birds repurposing antiavian architecture to jellyfish that can learn, here are dispatches from the animal kingdom that we went wild for in 2023.

Intelligent jellies

No brain? No problem. The fingernail-sized Caribbean box jellyfish (Tripedalia cystophora) uses its clusters of eyes and nerve cells to learn to avoid bumping into things, experiments in an aquatic obstacle course suggest (SN: 9/22/23). In the box jelly’s natural habitat, where the creature must swerve to dodge mangrove roots in murky water, it pays to be a good pupil.

Prehistoric pout

Tyrannosaurus rex’s menacing grin may have been less toothy than previously thought. Artistic renderings commonly depict the ravenous reptile as lipless, constantly baring its pearly whites. But T. rex may actually have had a pout that kept rows of pointy teeth covered, similar to Komodo dragons, an analysis of the skulls and teeth of dinosaurs and modern reptile suggests (SN: 4/22/23, p. 6).

illustration of a Tyrannosaurus rex eating another dinosaur
Tyrannosaurus rex may have had lips that hid its pointy teeth, as depicted here. Mark P. Witton

Revenge of the birds

City life can be hostile for birds. Municipalities across the world have put up spikes to prevent birds from roosting — and pooping — on streetlights, buildings and other structures. But some Eurasian magpies (Pica pica) and carrion crows (Corvus corone) in parts of Europe found a way to stick it to humans. The birds rip up antibird spikes and build nests with them (SN: 9/9/23, p. 4). Magpies may even use the spikes as humans do, to ward off avian pests.

A Eurasian magpie nest made out of antibird spikes in a tree
A Eurasian magpie nest made partly out of more than 1,500 antibird spikes sits in a sugar maple tree in Antwerp, Belgium.Auke-Florian Hiemstra

Swashbuckling spiders

Pirates on the high seas would be proud of their landlubbing arachnid counterparts. A species of cannibalistic pirate spider in Costa Rica tricks prey into walking the plank, right into its clutches (SN: 10/7/23 & 10/21/23, p. 11). Gelanor siquirres casts a silk thread to intercept that of an unsuspecting orb weaver trying to build a web. When the eight-legged victim scuttles across its own silk thread to secure the other end, the orb weaver finds impending doom rather than harmless vegetation.

A Gelanor siquirres spider
The spider Gelanor siquirres has a seemingly unique way of hunting other arachnids, tricking them into walking right into a trap.G. Barrantes, L. Segura-Hernández and D. Solano-Brenes/Animal Behaviour 2023

Desperate flies, desperate measures

Snow flies (Chinoea spp.) have a macabre method to survive the frigid mountains and forests they call home. Dozens of flies that researchers subjected to below-zero temperatures self-amputated their limbs, but only when the limbs began to freeze (SN: 7/15/23, p. 14). The flies probably shed the appendages to keep ice crystals from reaching the rest of the body.

Snow flies may drop one or more legs to prevent themselves from freezing. Even missing multiple limbs, one fly (shown here) can navigate over snow in the wild.

Self-aware fish

When it comes to brainpower, this fish is no small fry. Not only can the bluestreak cleaner wrasse (Labroides dimidiatus) recognize itself in a mirror, the fish can also identify a picture of itself out of a lineup (SN: 3/11/23, p. 13). The finding suggests the wrasse forms a mental image of itself — similar to what humans do — and that self-awareness may be more common in the animal kingdom than once thought.

a Bluestreak cleaner wrasse
Bluestreak cleaner wrasse can recognize photos of themselves, a possible sign that the fish have self-awareness.marrio31/iStock/Getty Images Plus

Tight-gilled sharks

Regulating body temperature in chilly water is a challenge even for scalloped hammerhead sharks (Sphyrna lewini). To stay warm while hunting in the deep ocean, the sharks use a method normally seen in diving mammals: They hold their breath (SN: 6/17/23, p. 10). Keeping gills closed holds in body heat, preventing the predators from becoming fish ice pops.

a group of scalloped hammerhead sharks swim near the surface of the ocean
Scalloped hammerhead sharks off the coast of Hawaii may close their gills to hold on to their warmth when diving hundreds of meters below the surface, new research suggests.Deron Verbeck

Big-mouthed snake

This African egg-eating snake redefines what it means to open wide. The Gans’ egg-eater (Dasypeltis gansi) can open its mouth wider than any other snake relative to its size, lab experiments suggest (SN: 10/7/23 & 10/21/23, p. 36). An egg-eater with a 1-centimeter-wide head could fit a cylinder 5 centimeters across in its mouth. The reptile edges out the previous record holder: the Burmese python (Python molurus bivittatus).

Open wide! This Gans’ egg-eater snake swallows a bird egg whole, uses its spine to crack the egg open, ingests the contents and regurgitates the shattered shell.

Disaster dogs

The irradiated zone around Ukraine’s Chernobyl Nuclear Power Plant might be off-limits for humans, but other animals didn’t get the memo. Packs of feral dogs that for years have roamed the area abandoned since 1986 are genetically distinct from canines of similar breeds that live outside the zone (SN: 4/8/23, p. 15). The differences probably aren’t due to radiation, researchers say. Whether Chernobyl’s radioactivity has had any effect on the dogs remains to be seen, but knowing their genetic makeup will help scientists spot potential radiation damage.

two free-roaming dogs in Chernobyl
Scientists have now performed the first genetic analysis of Chernobyl’s dogs. This pack of free-roaming dogs lives within the industrial areas of the former power plant.Clean Futures Fund+

Landscaping ants

Many ants are expert navigators who use local landmarks to find their way around. But what’s an ant to do when the world around them is almost completely flat and featureless? Desert ants (Cataglyphis fortis) in Tunisia’s salt pans take matters into their own mandibles. Workers build tall mounds over their colonies’ nests so wayward foragers can find their way home (SN: 7/1/23, p. 16).

A composite showing an image of a desert ant hill amid a salt flat and an image of an entrance to a desert ant hill tunnel with shrubbery and other plants int he background on the left
Desert ants (Cataglyphis fortis) that live in the interior of vast, flat salt pans in Tunisia build tall anthills (one shown at left) that help the ants find their way home. Other ants of the same species that live closer to areas with more visual landmarks build more typical, inconspicuous nests with only a small hole for an entrance (right).M. Knaden

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