Bouncing the flash is really of no value since, in this scenario, the camera system is attempting to expose for the background which is farther away. Whether the flash is set to shoot straight on or bounce is of no consequence when the automatic exposure system of your camera is attempting to gather light for a larger object. The spider represents such a small area of the image that the flash exposure system cannot discern that a sizable subject exists from which to measure the rebounding light when the shot is taken.
The solution is to compensate the flash exposure in your camera menu settings. You can set the flash exposure toward the underexposure side; i.e. dial in -2 stops, for example. The exposure will drop accordingly. In addition, you can go into manual mode to further control exposure versus the amount of power emanating from the flash. If you find that you cannot control the flash level to a low enough level for closeup work, you can add a neutral density filter to the lens to further knock down the light while setting the flash compensation to a minus value. If you don't have any ND filters, a polarizer is an automatic 2 stop attenuator. Hope this helps.