I hear horseshoe crabs are used for medical
testing. Are they killed?
August 12, 2004
No, they are returned to sea. Studies
do show, however, a mortality of three to 15 percent in
captured horseshoe crabs, but much depends on the care
the animals receive. They do well as long as they are kept
cool and moist. Many horseshoe crabs are recaptured year
after year with no harmful effects.
The crabs are collected in both deep and shallow waters,
using rakes or dredges. They are placed in a dark, refrigerated
truck and transported to a lab, where nearly one-third
of the crab’s blue blood is removed. The crab is
returned to sea and recovers fully in about a week.
The medicinal value of horseshoe crab blood comes from
its ability to clot in the presence of bacteria, rendering
the bacteria harmless. Even though bacteria are usually
destroyed by modern sterilization techniques, some bacteria,
called endotoxins, may survive the sterilization process.
This blood-clotting ability of the horseshoe crab makes
it very valuable in testing for injectable medicines, vaccines
and sterile medical equipment.
It’s interesting to note that horseshoe crabs live
in an environment teeming with bacteria, and, like many
invertebrates, lack an immune system. In such an environment,
even small injuries should be fatal. Yet, horseshoe crabs
have survived millions of years.
The horseshoe crab has also proved valuable to
the medical field in another way. Studies involving
the nerve pathways in the eyes of horseshoe crabs
have lead to many discoveries in human eye research.
The outer shell of a horseshoe crab is made primarily
of chitin. Scientists discovered that when used
as a coating for suture material and burn dressings,
chitin rapidly increased wound healing, cutting
the time by half.
Unlike human blood, which
is red because it is iron based, horseshoe
crab blood is blue because it is copper based.
Horseshoe crabs play an important role in the marine food
web, providing nutrition to large numbers of migrating
fish and shorebirds. They are used as bait and in effect
support a large commercial conch fishery in the northern
United States. The contributions they have made to human
medicine have saved countless lives.
Unfortunately, horseshoe crab populations are dwindling
due to habitat loss, water pollution and over fishing.
Efforts are now being made to reverse this trend. Losing
the contribution of this one animal could prove devastating,
not only to birds and marine life, but humans as well.