Fear of spiders is one of the most common phobias.
In most cases it stems from behaviour learnt as a child.
If you watched your mother scream as a spider ran across the floor, or jump on a chair to get out of its way, this sent a message to your sub-conscious brain that spiders represented danger to you.
Your sub-conscious would then trigger feelings of panic whenever you saw a spider, if left unchecked this behaviour will continue through into adult life and your children will follow the same example, thereby perpetuating the phobia into another generation.
I treated one man for this condition who told me that as a child he put his arm down the back of a unit in the garage, dozens of spiders ran up his arm, causing severe distress and panic to the child. These traumatic feelings had such an impact on him they stayed with him and everytime he saw a spider the panic and fear he had experienced as a child returned.
In countries which are hotter than ours it is of course wise to be wary of spiders, but in our country we do not have any venomous breeds, the worst than can be said is that they are an inconvenience.
In Hypnotherapy you can very easily retrain your inner mind and nuetralize those negative feelings enabling you to feel calm and relaxed around spiders.