A Willosaur's kill.
Blood effects were seen in Spore back in 2005 and 2006, but it was later toned down. It was never explained why it was changed, but some believe that it was because the developers wanted the game to be more appropriate to the general audience.
In the 2005 demonstration of Spore that was led by Will Wright, blood effects were part of the Creature Stage and Space Stage, and were probably going to be featured in other stages.
Cell Stage
Blood is actually seen in the final version of Spore, but only in the Cell Stage. If a cell has been poked or killed, magenta colored blood will appear. Also, chunks of meat have blood surrounding them.
Creature Stage
When Will Wright led his Willosaur in the creature stage it was shown attacking a smaller creature and blood spilled out of the prey. The Willosaur then proceeded to pull the creature's head off. (this method of killing was also removed because it was too violent). The Willosaur was then able to eat the creature more realistically than it does now, with bloody meat and the ability to drag the body away.
Tribal and Civilization Stage
In the tribal stage, when a creature is eating fish or meat, several drops of blood spill from the creature's mouth, like the Willosaur eating its kill in the creature stage.
It is unknown if there were blood effects in either the Civilization Stage.
Space Stage
It is known that if you abducted a creature and dropped it on a planet with no atmosphere it would explode in a shower of blood. However depending on the planet, the creature today will either burn, freeze, starve, or suffocate, but there is no blood. In an early demo of Spore, a sentient creature was dropped into a city, and there was blood.
Galactic Adventures
If you use the Missile Launcher on another creature in an adventure, a green substance will puff out like a cloud. It is unknown if this is blood or just a chemical byproduct of the weapon. It should be also noted that users can put blood into their adventures with any creation or option they can use. For example, they can make the water and the sand red, or they can use the pool effects to make anything bleed either white or green.
Other Games
Meditron spills the blood of his opponents.
Blood happens to be used in the game Darkspore, which caused a outrage among the fans complaining that there was too much blood and it was not realistic. Because of this, MaxisCactus said that the team is programming an option to turn the blood on or off. Therefore, when the player kills a enemy, it'll explode into E-DNA instead of blood. However, some of them were happy with the blood being there in the first place.