Horseshoe Crab—Lifesaving Living Fossil

Few animals have names more
misleading than the horseshoe
crab. It is not, in fact, horseshoe
shaped. If pressed to describe its form,
you might blurt out “frying pan” or “lollipop.”
For that matter, it’s not a crab
either but is classified as an arachnid,
more like an underwater scorpion than
anything else.

These creatures have “aged” well—their appearance hasn’t changed much
over the years. In fact, horseshoe crabs
are known as living fossils, creatures
that closely resemble their fossilized
ancestors. Creationists and evolutionists
alike note that horseshoe crab fossils
look almost identical to living specimens.
Evolutionists claim that the first
horseshoe crabs showed up in the fossil
record 445 million years ago, but biblical
creationists know that the earth is only
around 6,000 years old, and no fossils
are much older than the time of the
flood (about 4,400 years ago).

God’s design for this crab is, in turn,
provision for us. The horseshoe crab’s
intriguing designs make it a medical
marvel, benefitting humans and animals
alike and presenting Christians
with a unique opportunity to mitigate
the effects of the curse by wisely stewarding
God’s creation.

The Eyes Have It

One of the most uniquely designed
features of the horseshoe crab is its
visual system. It has 10 eyes, the two
largest of which are the lateral compound
eyes with about 1,000 photoreceptors
each. These lateral eyes contain
rods and cones similar in structure
to human eyes, though human eyes are
simple, not compound. The similarities
between horseshoe crab eyes and
human eyes have led to a better understanding
of human vision.

The horseshoe crab has five additional
eyes on the top side of its prosoma.
Each of these eyes is specially
designed to detect ultraviolet light,
allowing the horseshoe crab to see
reflected moonlight in and on the surface
of the water. Since the horseshoe
crab’s life cycle depends on spawning
peaks during new and full moons,
these five dorsal eyes are vital for the
horseshoe crab’s reproduction.

Two eyes on the horseshoe crab’s
underside near the mouth help it keep
its orientation while it’s swimming.
Finally, an “eye” (an interconnected
series of photoreceptors) on the tail
serves as an aid in helping the animal
keep its day and night cycles synchronized.1 For an alleged “primitive creature,”
the horseshoe crab boasts an
abundance of design features perfectly
suited for it to survive and thrive.

Blue Blood

Perhaps the most interesting aspect of
this creature’s design is its blood, which
is bright blue due to a high concentration
of copper. If you’ve ever had an injection,
vaccination, or surgery, you have most
likely benefited from the horseshoe crab.

For the past 40 years, this blue blood
has been at the center of an indispensable
diagnostic test for endotoxin. Endotoxin,
a component of some bacteria,
causes a severe immune response in
humans and many animals. If it enters
the bloodstream, endotoxin can cause
fever, toxic shock, and even organ failure.
Many vaccines, IVs, and implanted
devices (such as pacemakers and artificial
knee joints) potentially can carry
traces of endotoxins even after sterilization
and must be screened for its presence.
When vaccines, devices, and other
implements are tested for sterility, the
horseshoe crab blood clots in the presence
of endotoxin.2

In addition to being diagnostic for
endotoxin, horseshoe crab blood can
detect beta-glucans, which may indicate
fungal infections within hours,
whereas conventional diagnoses can
take up to a week.3 Horseshoe crabs
have definitely been a medical miracle
for mankind.

Horseshoe Crab Conservation

Since diagnostic tests require actual
blood from horseshoe crabs, the creatures
have become a staple of the
medical industry. They are raised in
aquacultures or caught commercially
and then bled in laboratories. Horseshoe
crabs can afford to “donate” up
to a third of their blood at a time, but
that much bloodletting is risky for the
crabs. An estimated 10–30% of horseshoe
crabs that are used for medical
bleeding don’t survive when returned
to the water, and those that do survive
struggle to thrive. Since the 1980s,
restrictions have been placed on harvesting
horseshoe crabs for commercial
or biomedical research, and state
parks and national sanctuaries have
been designated to help ensure that
crab numbers do not decline.

Scientists are initiating other conservation
and harvesting methods to
meet the increased demand for horseshoe
crab blood and to minimize the
need for their blood by developing the
use of alternative endotoxin tests.4
Thankfully, conditions have improved
somewhat for horseshoe crab blood
harvesting over the years, and more
improvements are on the horizon.

Provision and Compassion

The horseshoe crab’s enduring
design is confirmation of God’s
provision both for this unique
creature to survive and for
humans to benefit from its design.

The horseshoe crab’s enduring
design is confirmation of God’s provision
both for this unique creature
to survive and for humans to benefit
from its design. But we are reminded
in Scripture that “a righteous man
regards the life of his animal, but the
tender mercies of the wicked are cruel”
(Proverbs 12:10 NKJV). Compassionate
animal care is a biblical principle
of creation stewardship. As we work
to mitigate the effects of the curse,
may we be counted as good and faithful
stewards (1 Corinthians 4:2) of the
resources God has given us, including
the horseshoe crab.

Troy Lacey earned his bachelor of natural sciences
(biology/geology) degree from the University of Cincinnati.
Troy is a science writer on AiG’s content support team and
is the chaplain services and prison ministry coordinator for
AiG–USA.