Spiders

SPIDER!!!

Dolomedes probably means nothing to many people, myself included, and it has nothing to do with the very similar dolomades, a Greek stuffed grape leaf delicacy. Not even close. However, mention dock spider and, oh yes, that does come in loud and clear. Docky, as the spider of the year is inevitably named in our household – and invariably there is at least one that stakes out a territory on our dock – invokes fear and trepidation for almost anyone dangling legs in the water, gripping the swim ladder, or sitting in proximity to almost any nook or cranny around the edges of the dock. So here are some details that might help dissipate the fear if not the loathing.

Dolomedes is the genus name for this large spider that frequents docks, often seen with outstretched legs which make it seem even bigger than it is (and that is pretty darn big -up to 3 inches or so including appendages). Also known as fishing spiders, they do not spin traditional webs but rather detect surface disturbances on the water and make speedy forays to grab prey nearby. Some spiders are large enough and presumably speedy enough to trap small fish but insects, not dangling feet, are the usual food items, thankfully. They do inject venom to subdue the prey which is grabbed at first by claw-like structures on the spider’s legs. Fascinatingly, they also can dive beneath the surface and, surrounded by a layer of air, can even breathe while underwater. Their hairs repel water so they remain dry, and because of this air dry-suit, are very buoyant so they pop to the surface if they don’t find something to hold onto while submerged. Most of their hunting is done at night and the ability to sense vibrations outweighs any visible means of finding their dinner. You would think that with 8 eyes, 4 in each of two rows, their sight would be a primary hunting tool but not so. These vibration detectors also function as an early warning system for any predator such as a fish that might enjoy a spider meal! Are you less scared yet?

If not, here is more to add to the notion that knowledge is a great antidote to fear. There are nine species in North America. In Maine, two species can lurk, if you must, or at least set up shop on a waterside structure – Dolomedes tenebrosus, the dark fishing spider, which also can be found away from water, and D. triton, the six spotted fishing spider. Next time you see one, get a grip and try to see the spots. Actually, D. triton seems to have lines along its sides whereas D. tenebrosus is just simply dark. This later species exhibits a rather large discrepancy between the size of the female and the male, which is less than 1/2 the size of the female. Alas, males do not survive mating although it’s not from being eaten. Deemed ‘self-sacrifice’ in one on-line article, no other details were revealed.

Often in close proximity to the large female dock spider will be a web nest with tiny spiderlets, hundreds are them, (actually an egg sac can hold about 1,000, another amazing fact) that twitch in unison when the webbing is disturbed. Another common name for this group of spiders is the nursery web spider, a reference to this behavior. The female, exhibiting true maternal behavior, guards them after she attaches the hatchlings in their web to usually something inconvenient (for us) like the arm of a chair, the rope that wraps around a dock cleat or even the steering wheel of a boat. It is unclear to me what happens to all the baby spiders but they seem to decrease in number over time, maybe eaten by other predators or even each other? Survivors hibernate as immature adults in protected spots such as beneath rocks or behind bark of tree. In the spring, after a final molt, they mate and females carry their egg mass around until the spiderlings hatch. Tiny, they are cute; really they are!

Mama spider tending her eggs

Supposedly the venom of these spiders is not particularly strong or dangerous. We as a species seem hypersensitive to the idea of spiders but they are extremely important in the balance of nature, in their role as predator. Try to just let them alone, let the nests persist. They are interesting to watch, add to all the wonders we call life and probably very few survive. Otherwise, well, let’s just say that we would be even more likely to post a sign on the ramp to the dock that reads “Beware of Spiders.”

Reference:

  • Insects: Their Natural History and Diversity by Stephen A. Marshall
  • Dolomedes, Wikipedia, the free encyclopedia, https://en.wikipedia.org/wiki/Dolomedes
  • Genus Dolomedes – Fishing Spiders, http://bugguide.net/node/view/1985
  • Maine spiders – http://www.spiders.us/species/filter/maine/
  • Canada’s Largest Spider – http://arthropodecology.com/2012/08/13/canadas- largest-spider-sittin-on-the-dock-of-the-bay/

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