The Northern Kelp Spider Crabs can grow fairly large. This species seems to use less decoration than other spider crabs do. It has two rows of hooked setae just behind its rostrum, to which it sometimes attaches algae or kelp, etc. Unlike other decorator crabs, the items it attaches are usually food to eat later.
The Northern Kelp Spider Crabs eat algae and kelp. When these are scarce they may eat barnacles, mussels, and plankton. It, in turn, is eaten by stag horns, sculpins, gulls, cabezon, and the sea otter.
The species is sometimes parasitized by barnacles which causes the crabs to be sluggish and to have a brownish mass (the reproductive parts of the barnacle) can sometimes be seen protruding from under the abdomen.
The long legs and claws of these crabs are strong, and they can pinch hard quite hard, so be careful when handling them.
Females can be seen carrying eggs throughout most of the year. The females are absent for several summer months each year, and it is thought that they move to deeper water to lay their eggs.
A female may lay as many as 84,000 bright orange eggs, which then begin to change colour to a deep red as embryonic development ensues. The eggs take about a month to hatch into tiny larvae.
Sometimes you can see them, when they are small, hanging onto kelp as it sways in the current. This is almost hypnotic to observe. When there are a number of them together, it is almost like watching ballet dancers.
These little creatures have been fascinating to me since the first time I saw one, I must have been only 6 or 7 years old and was completely spellbound by them, They are such wonders to observe.