TYBEE BEACHCOMBER | JAN 2020 13
MANTIS SHRIMP
One reason that Tybee Island is such a good place for marine biology
diversity is because it is fairly small with inlets at both ends. The south
end inlet is pretty much just ocean water moving in and out with each
tide. However, the north end inlet is the entrance of the Savannah River.
So even our two inlets, just a couple of miles apart, are different with
different sources of water and different hydrological characteristics.
These conditions produce another set of environmental variabilities that
contribute to Tybee’s biological diversity.
Behind the inlets are salt marshes and estuarine habitats. With this close
proximity and constant tidal flow of water in and out, it is not surprising
that we often encounter estuarine animals out along the beach. One good
example of this is the Mantis Shrimp.
Mantis Shrimp aren’t really shrimp (like we eat), but instead are classified
into their own group of Crustaceans. Actually they are a fairly primitive type
of Crustacean, but as often happens, if they look sort of “shrimpy-like,”
they are called some type of shrimp. They get their “mantis” name from a
pair of appendages or legs under the front part of their body. These legs
fold back on themselves, so they look similar to the “praying” legs of a
Praying Mantis insect.
Don’t let those “praying hands” deceive you. In reality, those folded
legs are powerful and effective tools for defense and for catching food
(the other “prey”). The legs can be extended out and then folded back in
to function as pinchers for catching and holding food. The inside edges
of these pinchers have a few sharp, pointy sections, so if something gets
grabbed, it is not likely going to get away. Just the pinching action is scary
enough to keep me from handling them!
Their legs have muscles inside that not only cause the joints to pinch
inward but they can also extend them outward with great force and speed as
well. That means that the sharp pointed end of the leg can suddenly extend
outward to spear passing prey or to defend itself. This rapid extension is
one of the fastest muscle movements in the animal kingdom. I’ve heard of
reports of Mantis Shrimp actually cracking aquarium tanks with their spear
hitting the glass. One more reason I don’t handle them!
Many years ago, when working on a shrimp boat in North Carolina, we
frequently brought up a few Mantis Shrimp in the nets. The crew called
them “thumb busters” and usually shoved them aside with a trowel, rather
than their hands, when picking through the catch.
Normally Mantis shrimp live in burrows in the bottom in estuarine areas,
but we find them occasionally during our Tybee Beach Ecology Trips,
especially when hunting for Ghost Shrimp which also live in burrows. In
a bucket of water, Mantis Shrimp are very acrobatic and active and fun to
watch. But you don’t want to try to hold it in your hand!
Dr. Joe Richardson (Ph.D. Marine Sciences) is a retired marine science
professor with 40 years of research and teaching experience along GA, the
southeastern coast and Bahamas. Besides research, he conducts Tybee
Beach Ecology Trips (www.TybeeBeachEcology.com)
Beach Walks
with Dr. Joe
By Dr. Joe Richardson
/(www.TybeeBeachEcology.com)