|Only the tail, fins, eyes, and mouth stick out of
a boxfish’s boxy suit of
armor, which is created
by linked scales.
Penetrating the Armor
As populations of animals change over time, they develop defenses.
Predator populations also evolve, developing body parts and
behaviors that help them defeat their prey’s defenses. Often this
simply involves big teeth and strong jaws. A shark or crocodile,
for example, can easily crunch through a turtle’s shell. Sometimes,
however, special behaviors are involved.
The bearded vulture, for example, knows how to open turtles’
shells. This vulture is found in parts of Europe and Asia. It
mainly feeds on animal bones left over from other animals’ kills.
To get at the food left inside a bone, the vulture carries the bone high into the air and drops it onto rocks to smash it apart. The
vulture uses this same behavior to smash open a turtle’s shell.
Gulls use this behavior, too. They carry clams and other
shelled animals into the air, and then drop them onto rocks
and roads. Crows likewise drop snails onto hard surfaces. Song
thrushes hold snails in their beaks and bash them against favorite
stones, which are known as thrush anvils.
A bird called the snail kite is named for its habit of eating
almost nothing but apple snails. Its slim, hooked bill fits neatly
into the spiral of an apple snail’s shell. The bill’s sharp tip snips a
muscle in the snail, releasing the snail from its shell.
The oystercatcher, a bird that feeds on ocean shores, patrols
shellfish beds to look for mussels or oysters with slightly opened
shells. The bird stabs its long, sharp bill into one of these open
shells, quickly cutting the muscles that clamp the shell closed.
An oystercatcher may also open a shell by bashing at the hinge
from the outside.
A sea snail gets past a clam’s armor by using its raspy tongue
to drill a hole in the shell. A sea star wraps its suckered arms
around a clamshell and pulls. Eventually, the clam gets tired and
the shell opens. Immediately, the sea star’s stomach oozes out of
its body and into the shell, where it digests the clam.
A sea star can even slip its stomach around a sea urchin’s
spines. A sunflower star is big enough to engulf a sea urchin and
digest it, then “spit out” the shell and spines. A triggerfish also
eats sea urchins. It flips them over, plucks off their spines, and
then uses its strong teeth to bite through the shell.
Mammals have figured out ways to get around their prey’s
armor, too. A weasel-like animal called the fisher, for example,
quickly flips over prickly porcupines so it can attack their soft
undersides. Wolves, wolverines, and bobcats also prey on porcupines.
A sea otter carries a stone underwater and uses it as a
hammer to knock sea snails called abalone off rocks.