Make up a spray bottle of mint.... both ants and spiders hate it.... you might also plant some around the dock.
I have seen this before and am going to buy some mint plants. Thanks for the reminder!
Hi Ernie: The most popular spider control product for use around water is Essentria IC3, because it is effective for spiders, kills most other insects (eliminating the spider's prey which will help keep new spiders from moving back into the area) and it safe to use around water. Most other insecticides are prohibited near the water because of the risk of contaminating the water and harming aquatic animals. You will need to repeat the application once a month through the warm season.
I have used Ortho Home Defense, and it seems to work wonderfully. Even when it's dry, it keeps killing bugs for about 6 months! I think if it rains, you may have to respray. But, I've used in in my house for years and it doesn't smell and really works. However, don't spray it where people or pets walk, because it is still working for 6 months, barefeet or pet feet can absorb the poison, so keep it where no one or no pet walks, also the railings where hands go and birds sit. Otherwise, spray away:)