Invasive SpeciesGreen crab

Carcinus maenas
FOUND by csteingart
Monhegan Island
ID Confirmed
Quality checked by vitalteach
Peer reviewed by vitalteach
Field Notes
My husband and I came across a very unusual green crab while visiting Monhegan Island...a WHITE green crab! We were beachcombing for sea glass on a shore called Fish Beach when suddenly he saw something scurry under a rock. We carefully raised the rock and found a tiny green crab, about one-inch in width, displaying unusually bright white markings. I had an empty sandwich bag, filled it with seawater, and placed the crab inside it (I hold a State permit to collect marine organisms for educational purposes). Once I got home to Yarmouth, I began showing the crab to various professors, marine experts, fishermen, and students. So far, I haven't found anyone that has ever seen a green crab with such unusually white markings as this one. For nearly 2 months I've enjoyed the opportunity to connect with marine experts and enthusiasts alike, showing off the WHITE green crab. I even exhibited the crab to a variety of marine educators last weekend at the NEOSEC Ocean Literacy Summit at UNH. Curious onlookers enjoyed seeing the unusual white color pattern not normally seen on a green crab of his size. I've also been fortunate to have shown him to many elementary school children, college students, and assorted marine enthusiasts throughout the past couple months, not to mention the hundreds of people that saw him via the internet photos posted. He was truly a celebrity in his own right and will be missed by many people that got to meet him.
Supporting Evidence
Photo of my evidence.
We carefully raised a rock at Fish Beach and found a tiny green crab displaying unusually bright white markings. I compared the brightness of the white color to that of White-Out. Unlike a true albino, there were dark striations outlining each white section resembling a mosaic pattern. Upon further investigation, holding the crab in my hand, I quickly realized that it had just molted because the shell was very soft.
Photo of my evidence.
The green crab was about one-inch in width.
Photo of my evidence.
After 39 days in my home aquarium, the crab molted. After he molted, we measured the two carapaces. The pre-molt carapace measured 20mm. The post-molt carapace measured 25mm. That shows a 25% increase in carapace size. The molt revealed the same white pattern on its new carapace (shell). Throughout this period, it was suggested by Professor Larry Harris at UNH, to place white copy paper underneath the tank which may in fact have been the reason it molted white again. Scientists who have done studies with green crabs have found that juveniles are highly variable in color for camouflage reasons. They often range from black to green to red to white. Once they mature to adults the color variability disappears resulting in the more common greenish-brown mottled color we are all familiar with.
Species Observation: Species Looked For
Did you find it?: 
I think I found it
Scientific name:
Carcinus maenas
Common name:
Green crab
Sampling method: 
Just looking around
Photo of our sampling method.
Place Studied
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Map this species
N 43.763225 °
W -69.321603 °
Observation Site Information
A photo of our study site.
Coastal - Rocky intertidal
Trip Information
Monhegan's Fish Beach
Trip date: 
Sun, 2010-09-26 10:00
Town or city: 
Monhegan Island
Type of investigation: 
Species Survey
Monhegan Island
Time of low tide: 


This is a very nicely done write up about the crab. I found the molting experiment to be very interesting and would like to hear more if you tried other colors. Also, the photos you took were nicely done. Thank you so much for sharing.
Chandra Nizamoff

Whilst at gullane bents, Scotland,UK we found a crab which was very unusual Scotlands marine ecologist says he has not seen it before after weeks of searching I found your page.

Thanks for sharing Kittenkatkez. Great photo!

Very cool, sounds interesting Kittenkatkez. You can email us the photo at

I'm afraid the WHITE green crab has bit the dust, literally. He escaped from a temporary feeding bowl while my back was turned. My husband and I scoured the living room and dining room floor together on our hands and knees. My husband found him underneath the baseboard in a little wooden depression. He wiped off some dust and put him back in the aquarium. The next day he was dead. My husband deduced that the white dust under the baseboard was an insecticidal dust used for eradicating carpenter ants. It was applied under the baseboard in June 2008. For the carpenter ants, it's a good thing that it still retained its effectiveness. For the crab, it was a lethal end to a very exciting public life.

This is a beautiful specimen! I was very interested to hear about the white paper and the molting experiment - very neat stuff! I believe I met you (and your crab) at NEOSEC on Friday. We shared a table at the intertidal critter activity, and I mentioned that Robin Seely had been my advisor. If you still have your crab, I would be interested to see his future molts!
All the best,
Elizabeth Stephenson