Crab Photos
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The key rules to determine what is the species name of the crab you are holding:

Asian shore crab have three teeth on each side of the eye. Three is the fewest
number of teeth on each side of the eye that you will find on any crab.
This crab is also one of the smallest crabs on the New England coast.

The Chinese Mitten crab has 4 teeth (lateral spines) and is not found on the New England coast. If found, please collect, kill, and send that to me or MIT Sea Grant.

European Green crabs have 5 teeth on each side of the eye.
How many letter in the word "green"? 5.
How many teeth on each side of the eye on a European green crab? 5.
This is a great way to know if you find a crab with 5 teeth on each side
of the eye it is an invasive European green crab.

The native crabs, jonah and rock crab, both have 9 teeth and grow larger than
both the invasive crabs. So if the crab has more than 6 teeth on each
side of the eye the crab is native. These two crabs are very hard to
differentiate but that is OK because they are both native.

The Chinese Mitten crab has 4 teeth (lateral spines) and is not found on the New England coast. If found, please collect and store in ethanol. Please send a picture of your find and the location it was collected to:

Two actual pictures of this species are below. It is one of the 100 worst invasive species!

The Usual Suspects:
img271.jpg crab drawing 5 teeth 1111.pngimg30.jpg

European Green Crab (Carcinus maenas)

On the left, notice the 5 teeth on each side of the eye. The number of teeth on each side of the eye is vital for proper identification.;; 2004/homer-crabs.html


c maenas color 2.png


C. maenas (European green crab)
Here is a specimen drawn in Color.  This is the green color but they can be any color: red, brown, algae covered. Don't be deceived if you find a red "Green Crab".  It lives in sandy beaches and lagoons of esturaries (where fresh water of a river and salt water of the ocean mix and create brackish water)  and rocky beaches.


c maenas male and female.jpga red c m.jpg





Both sexes of what species of crab?

On the left is a male green crab. Notice the tail flap is thin and shaped like a light house or the Washington monument. On the right is a female green crab. The abdomen (tail flap) is wider and more rounded. Notice the C. maenas (green crab) is red.


What is the species and sex of the third crab (the one furthest to the right)?

It is a European green crab!  Did you get tricked? This is a great lesson. ezidweb/grncrb01.htm


c maens berried female.jpg

A berried female C. maenas:
Belly shot of a gravid (pregnant) female crab.

The female invasive crab has her eggs under her rounded tail flap. She can carry as many as 185,000 - 250,000 eggs in a single brood. They may have one or two broods in a breeding season (late April to September). 



Asian shore crab (Hemigrapsus sanguineus): This crab is smaller than the European green crab. It have a more squarish body (carapace) and three teeth, instead of five, on each side of the eye.


Their claws are larger in comparison to their small body size. Notice the and brown and tan mottled color.


The crab resides mainly in cobblestone and rocky beaches. They have also been reported to be found in the chinks of metal chains on docks and moorings.


a hemi male1.png

Is this a male or female Hemigrapsus?


It is a male since the tail flap (the small darker section of the carapace) is shaped like a light house!


hemi penny

They are small but are strong and must be stopped!
This species is small with adults ranging from 35 mm (1.5 in) to 42 mm (1.65 in) in carapace width.


a range of shorecrabmap1a.gif



The Native Species:




Rock Crab - Cancer irroratus less distinct 9 spines and grow to larger sizes. These native crabs live more subtidal, so you may not find this crab. Its numbers have been lowered due to the thriving populations of invasive crabs, the European and Asian shore crabs. 


Jonah Crabs look almost exactly identical to Rock crabs due to similar color and possessing 9 teeth on each side of the eye. So although it is hard to identity these 2 crab species, it is not that important since they are both native. This is not ideal but is probably needed since the two crabs are very similar in appearance and only vary by behavior and one has slightly more frilly teeth.


My research cares more about the densities of invasive and native crabs, so it is not vital to determine if the 9 teethed crab is a jonah or rock because we know for sure it is a native crab. This is why the best way to identify crabs is by the number of teeth and not color. Native crabs have 9 teeth while the invasive European green crab is the only one you will find with 5 teeth and the Asian with 3 teeth on each side of the eye.



Rock Jonah have black coloration on their pincers.


Blue Crab: Native crab that has the flattened tail of the swimmer crab.


Another blue crab.


Best Ways to pick up crabs?


This picture shows one of the two best ways to pick up a crab and not get pinched. What type of crab is in the picture? How did you tell?


If you said color, give me a better and more solid answer!   


The color can be deceiving but in this nice picture, you can see the 5 teeth of the invasive European green crab.


The other best way is again to use two finger but on the backside of the crab.





Photos courtesy CA Dept. of Fish and Game
Info for ID


Here are pictures of the first CSI Detectives! This great group from Boston went out during the rain and collected the first set of data on Georges' Island in
Boston, MA! Many thanks to them, they exemplify what CSI: MISMO is all about. Rain or shine, going to the coast and collecting important data!
A million thanks for these great efforts.  Here are the pictures, not sunny and bright, but the data is so important!

6th Graders from the Harbor Middle School, a Boston public school, working through Harbor Connections; in collaboration with the Boston Harbor Islands national park area.



Crab Carapace Quiz:






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