For the most part blue whales are too large to have any known natural predators.
In fact the only known predators to attempt to attack a blue whale is a group of killer whales.
While these instances are rare there have been people who have confirmed witnessing such attacks.
In these attacks a large pod of killer whales are usually spotted working cooperatively in an attempt to try to successfully take down a blue whale by surrounding it from the front, sides and bottom to hopefully prevent it from escaping.
After blocking the whales escape they take turns biting the blue whales blubber and flesh and will continue to wound the whale until it becomes too weak to fight or flee.
Some killer whales may also charge the blue whale and attempt to leap onto it’s back in an effort to further weaken it.
When the adult blue whale appears to be too much of a fight for the killer whales they may attempt to separate the adults from their child and will attack the defenseless young whale in the hopes of successfully capturing a meal.
For killer whales attacking the young blue whales often provides them with a much better opportunity for making a successful kill as young whales may only measure in at 25 – 30 ft. long and are typically less experienced on how to defend themselves.
While these attacks do happen they seem to be pretty rare (assuming there is easier prey for the killer whale to hunt) and it also seems that their chances of successfully attacking a blue whale is rare as well.
In many cases the killer whales eventually end up giving up if the pursuit takes too long, which in some cases could last for hours.
As far as other predators are concerned humans still remain the primary threat to blue whales.
Most countries have adopted rules that ban whale hunting, however there are also several countries that still endorse this type of activity.
In the countries that still hunt blue whales it is usually for their meat which is considered by some to be a delicacy.
Other threats blue whales are currently facing include waste pollution, noise pollution from sonar and other man-made sounds, collisions with boats, fishing nets and global warming.