Pirate or otter spiders as they are now often called are a genus of wolf spider (Lycostidae) that live in and around water. The name pirate spider can cause some confusion with another group of spiders in the Mimetidae which are also called pirate spiders, due to the their hunting strategy of plucking the threads of another spiders web to simulate insect prey, only to catch and eat the spider that comes to investigate.
However the spider being referred to here is the Piraticus species, which like the raft spiders (which belong to a related family) they can run and stand on water, catching prey that are on or just below the surface. Prey includes the young of smaller Pardosa sp. wolf spiders and invertebrates that have fallen on to the water’s surface. Like raft spiders they can sense the movement of prey through vibrations in the water’s surface, though of course due to their much smaller size (9mm body length max) they take much smaller prey.
Unlike raft spiders, it does build a web, it is tube shaped, often in some moss or vegetation and used a home rather than to catch prey. They are most often seen in late spring and summer in and around aquatic habitats.
In some wolf spiders the male attaches the female with elaborate movements of the abdomen and legs, the latter of which is often covered in marking of long hairs. In pirate spiders however thy lack the markings and signal hairs and the courtship is described in comparison as short and less conspicuous, and not including pronounced leg or abdomen movements.
Once mated the female lays her eggs, wrapping them in a cocoon which she carries with her everywhere, attached to the end of her abdomen, as opposed to in her fangs as in raft spiders. She will bask in the sun to warm them and speed development and have been seen hanging their egg cocoons out he end of their tunnel web, keeping them selves cool in the shade and the egg cocoon warm in the sun.
Once the eggs hatch they crawl on to their mothers back where they stay until they are ready to fend for themselves.