What is good for killing spiders on boats?

Answer 1

There are a few things that could kill a spider on a boat with extreme prejudice. A great choice is your foot. Shoes help, but if you desire maximum stomping power, steel-toed boots work great. Crowbars are also effective, as one good blow will kill a spider (or headcrab) of any type or size.

Answer 2

Spiders are not particularly resistant to insecticides, but why would you want to kill spiders there? The only spiders that sort of deliberately hang out on docks are the spiders that are adapted to living on and near the water. Guess what they eat. Unless you want more house flies, horse flies, deer flies, no-see-ums, etc., etc., you are probably better off with the creatures that like to kill and eat them.

Insecticides can also kill fish, no? On top of that, it is not clear whether insecticides are causing die-offs of honeybees and autism. When you apply insecticides it is impossible to make sure that only insects get poisoned by them. Poisoned insects get eaten by song birds, and they may have reproductive trouble. Frogs and other amphibians are in trouble the world over, and it is possible that they may be being hurt by insecticides.

If you had to keep spiders out of someplace the safest thing you could do would be to apply diatomaceous earth. You can get that anywhere that sells garden goods. It is just the razor-sharp shells of diatoms that died millions of years ago. It kills insects by mechanical action. The "blades" are not big enough to hurt humans with bare feet.