Shooting straight down on a snake like that with camera mounted flash is difficult. A polarizing filter may help a little...that will be trial and error with a flash. If you can bounce and diffuse the flash, you'll get better results. I'm not sure what kind of camera you are using and if it allows for control of the flash or using slave units.
If you can get a more front-on angle and bounce the main flash from above-left or above-right, then use a small flash unit as a slave off the main flash for frontal fill-flash, it will eliminate a lot of the glare and wash-out. Make sure that your focus point is the snake's eye, then adjust for depth of field by using the aperture setting. A depth-of-field preview is very handy for that.
I'm not very familiar with digital cameras, so I'm not sure how much control you have over these things.
I use a Canon EOS-3 (35mm film camera) with a Speedlight 550 EX main flash and a cheapo smaller unit for fill flash, a Tamron 90mm Macro lens, an old Slik U-212 tripod and a box I made out of plywood with a bottom, 2 sides and a back that are painted white to reflect flash. The front is open. The bottom dimensions are 32" x24", the sides and back are 18" high. I can build whatever background I want to use in the box, set the camera and flash up, pose the snake and burn film. I use white poster board above the box to bounce flash downward. I always use the mirror lockup and an electronic remote trigger for macro to reduce vibration. For small snakes, I just put a deli cup over them and let them coil up naturally and settle down, then gently remove the cup and shoot before they try to take off. Many time if your timing is good, you will catch that alert, head up posture (and maybe some tongue-flicking) when they realize the cup is gone.
OK...so I'm a dinosaur, still using film. Canon makes a professional quality digital body for my lens system, but last I checked it was over $8,000.00 for just the body. A little too pricey for me. I can buy a lot of 35mm film for that.