After the death of James' parents, the two had no choice but to take in James and "raise" him. Instead of caring for him, they force him to do all the work around the house, they had a tendency to beat him when he disagrees with them or backtalk, and almost always make him go into his room without dinner.
Aunt Spiker is a strikingly tall, skinny, and cold (on the inside) woman. She's probably the older aunt. Spiker also seems to be the smarter one of the two.
Aunt Sponge is a short, fat and ugly woman. She's usually the one who beats up James and eats the most. She claims that she is a very beautiful woman like her older sister Spiker, but looks beg to differ. She is also not as smart as Spiker.
Aunt Spiker and Aunt Sponge adopted James after his parents were eaten by a rhinoceros and are very abusive and treat him like a slave, forcing him to do hard labor and feeding him nothing but fish heads. Aunt Sponge is fat, loud and ugly whilst Aunt Spiker is thin, quiet and cold. Both have a terrible hatred of insects and bugs and kill them in a variety of awful ways, and are thus hated by them as well. It is unknown which one of James's parents was Spiker and Sponge's sibling.
Sometime later, Spiker and Sponge discover a peach on a withered old tree, and watch it grow to immense proportions in a matter of seconds. Spiker and Sponge use the giant peach as an attraction, making lots of money as James watches from the house, not allowed to leave or play with the other children. That night, Spiker and Sponge send James outside to pick up the garbage dropped by their customers.
Later, when James escapes on the giant peach, he is followed by his two persistent aunts all the way to New York, apparently somehow managing to drive their now crushed car under the ocean and reach New York covered in seaweed and crabs, where they try to convince the authorities that James is a liar and that he be released to them. However, James, now no longer afraid of his cruel aunts, stands up to them and reveals the truth about their horrible treatment of him. Unable to believe that James dares to stand up to them, they furiously attack him with firemen's axes until the sudden reappearance of the insects. He then ties them up with Miss Spider's thread, and the beat cop has them taken away on a crane.
After the credits, there's a scene showing an arcade-like game which consists of controlling a rhinoceros to attack replica models of the aunts.
In the book, when the peach gets loose and rolls, it flattens Aunt Spiker and Aunt Sponge, killing them both, and they subsequently do not reappear at the end.
In the 1996 film, they survive and pursue James to New York City in their beat-up car (in the Ice World, James and Miss Spider see a shipwreck with figureheads, having a terrible resemblance of the two aunts). Upon arriving in New York, both are soaked as if they had been driving their car across the seabed. They attempt to kill James but are tied up with Miss Spider's silk and arrested.