The Grim Adventures of Billy and Mandy Wiki

No more Mr. Nice Spider.

Jeff the Spider is a giant Underworld spider monster and Billy's (unwittingly-) adopted son. In Underfist: Halloween Bash, he serves as a major character.


He is a giant spider with four green eyes and a red hourglass-shaped pattern on his back. He also has white fangs, white upwards-facing chelicerae and white claws for fingers. At times, his claws, fangs and chelicerae can appear to have a slight greenish hue. In early episodes his body is completely black, but later it is black and purple.


Jeff is described by Mandy as being both "too nice" and "basically insane". True to her description of him, Jeff is gentle and kind to an unnatural and manic degree. Despite being beaten and abused by Billy, he holds no ill will towards him at all. It may be impossible for Jeff to be mean, as Jeff claims to have a very small "mean gland", and the only reason he blew up at Billy during the Wrath of the Spider Queen was because of Arachnotaur's presence within his body.

He is somewhat childish, as revealed by his friendship with the inane and foolish Fred Fredburger. He attempts to act more like an adult during Underfist, reading the paper, wearing wigs and adult diapers, but he and Fred decide that they like being childish better, and Jeff becomes happy with this.


For reasons unknown, and that were never touched upon in the series, the spider egg that contained the spider that would become known as "Jeff" was stored inside Grim's magical trunk. Given that the natures of the items that Grim usually stores in his trunk are items that are cursed or dangerous, Jeff's species is probably dangerous. Jeff's species is very venomous and also capable of carrying the highly contagious Spider Pox. He is friends with Fred FredBurger, as shown in Underfist: Halloween Bash.


Jeff the spider made his first appearance in The Crawling Niceness. Billy, despite having been told not to, went rummaging through Grim's trunk and found an egg. The ever-dense and deluded Billy, thinking he would get a giant duck if he were to hatch it, went forward with 'incubating' it. Instead of warming it, Billy's rump broke the egg open. Billy laments that if a duck had come out of the egg, he would have named it 'Jeff'. This caused Jeff to believe that Billy was his father, ironically, in the same way ducks imprint on their mothers.

When Billy awakens the next morning, Jeff is able to speak full sentences and has grown from about the size of a small mouse to the point that he's towering over Billy. Jeff spends the episode trying to impress and be kind to his 'dad', which unfortunately backfires on him, as Billy is severely arachnophobic. At the end, he moves in with the story's narrator, an exterminator, who he is seen making pancakes for.

Later Episodes

Jeff's next major appearance would be in Spider's Little Daddy, where he is shown living in a dirty old outhouse in Endsville park. After meeting up with Billy during the Endsville father-son picnic, he seeks help from Mandy on being more assertive. His inability to be negative even for a minute finally forced Mandy to get up, but after overhearing Mandy say to 'go crazy' he eventually finds his backbone and demands affection from his dad.

In Spidermandy, Jeff becomes sick with the 'Spiderpox' and decides that the best way to get better is to have his dad take care of him. Billy unwittingly becomes the carrier of Jeff's spiderpox and transmits it first to Mandy and eventually to the rest of the town. When Mandy is turned into a spider by the Spiderpox, Jeff is elated at the prospect of finally having a mother. His venom cures Mandy, but unfortunately for the rest of Endsville, he's sent away by Billy and not able to fix everyone else.

Gender Issues

Jeffy's Web (and later Herbicidal Maniac) bring into question Jeff's gender, as 'he' lays hundreds of eggs and attempts to find a home for them, noting that many spiders die after laying eggs. Despite this, Jeff has been established as a guy. 

However, since he was able to lay eggs without coming into contact with another giant spider and he’s a spider monster from the Underworld, his species may actually be able to reproduce asexually. Also in Jeffy's Web, Grim showed what Jeff’s Hourglass of Death looks like and it is shown to be small and pink giving further question to the gender.

Episode Appearances




Jeff seems to love his father and always tries to be nice to him. Even when Billy keeps stabbing him with a stick, he never gets mad at Billy (even though Billy never remembers his birthday, or pays child support, and always treats him badly).


Jeff seems to love Mandy and always goes to her for advice about his father. Unlike Billy, Mandy seems to be a lot kinder to Jeff than Billy is, and never throws things at Jeff like Billy does. She always gets Jeff to stick up for himself when his father won't give him any love.


  • Jeff laid eggs in "Spider's Little Daddy", leading himself and Billy to assume he's actually female, though this is likely untrue, with no other references to this being made.
  • Jeff is an exceptional chef.
  • It is later revealed in the 'Wrath of the Spider Queen' that Billy never lets him see his mom and apparently never pays child support.
    • 'Mom' may refer to Mandy, as he considered her his mother Spidermandy and she always seems to offer him advice on Billy.
    • It also may refer to Jeff not knowing who his mother is, and assuming Billy does.


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