Adder is a snake who makes the journey from Farthing Wood to White Deer Park in both the books and the TV series. Adder is male in the books, but is female in the TV series. Adder shows very little emotion to the other animals and is seemingly uninterested in upholding the oath.
However, Adder does help the other creatures on many occasions; such as saving Vixen from the hunt and distracting Jack while the other animals escape from the farm. Having originally isolated himself/herself in the park, Adder grows fonder of the other animal`s company over time and acts in a much more friendly manner late in the series.
Story[]
The Animals of Farthing Wood[]
Adder is the last to arrive at the assembly and shows very little interest in the proceedings, but starts to take interest when Toad tells the group about the edible frogs. On the journey he makes several sarcastic and unhelpful comments which causes the other animals to question his value to the group, but he is not interested in what they think of him.
When the animals reach the swimming pool Weasel suspends him over the water to drink in his teeth, but drops him in the pool when the animals sense they are being watched. Fox eventually helps him out with a cane he finds in the garden.
Adder struggles to cross the trunk road and is nearly run over, but the car turns at the last second and misses him. While the animals are trapped in the farm storeroom, Adder distracts the guard dog Jack allowing the others to tunnel their way out.
The other animals leave him behind but Tawny Owl is sent back to collect him. At this point Adder begins to sense that Tawny Owl sees himself as a potential leader of the group and teases him about it for the rest of the journey. During the hunt, when the hunt master is bearing down on Vixen and is about to strike her, Adder appears and sinks his teeth into the horse's leg, causing it to rear up and the hunt master to fall to the ground.
At the quarry Adder criticises Toad's decision to let the carp go free and later tries to catch the fish himself. Adder refuses to cross the motorway as he sees no way of making it across safely, but Whistler picks him up and carries him across.
He is among the slower animals who is left behind after escaping the church, but Whistler is sent to collect them. When the animals reach the park Adder spends his time by the pond, hoping to catch one of the edible frogs, but he never manages to catch a single one.
In the Grip of Winter[]
When winter starts to arrive Adder goes into hibernation with Toad and sleeps until spring arrives. When he resurfaces Adder tells the other animals that Toad's homing instinct must have caused him to head back towards Farthing Wood.
He shows very little desire to join the other animals and make the party complete for the first time since the start of the winter, but he does agree to join them in celebrating their survival through the winter.
Fox's Feud[]
Adder attends the meeting to discuss the problems the animals are having with some of the park's inhabitants, but does not take much interest in proceedings and makes several sarcastic remarks. He later talks to Bold as the young cub is heading off towards Scarface's territory and, when Bold fails to return, he tells Hare to inform Fox that Bold has gone missing.
While Fox and his family are searching For Bold, Adder tells The Great Stag what is happening and the stag intervenes in the feud, allowing Fox to safely leave Scarface's territory.
Bold and Friendly are sent to tell Adder to kill Scarface, but they are not specific enough and Adder kills another fox, believing this is what Fox wanted him to do.
When he learns of his mistake he goes into hiding and fasts to preserve his venom for Scarface, but he is forced into the sun to regulate his body temperature and is seen by Ranger.
He tells Scarface, who goes after Adder and bites off the end of his tail, but the snake is able to escape into a small burrow.
After Scarface leaves, Adder comes out again to sunbathe and tells Toad about his recent encounter. After this, Adder waits by the stream for Scarface and when the old fox starts crossing the stream to get home after his killing spree in Farthing Wood land, Adder sinks his fangs into Scarface's leg, releasing his full store of venom.
Adder watches on as Scarface slowly dies, and then heads off to inform the other animals of his triumph.
The Siege of White Deer Park[]
Adder finds some large footprints near the pond and asks Toad to confirm whether they have been made by a large mammal. After Whistler informs Adder that he has seen The Beast, Adder goes in search of the cat with the intention of poisoning it, but the Beast traps him with its paw and toys with him.
Adder is eventually knocked into the stream and he is able to escape. He later comes across a female adder and tries to impress her by telling her about his encounter with the Beast, but she shows no interest in him.
But he meets the female snake again and she tells him about the Beast's lair by the stream, so Adder informs Whistler who heads off to tell the other animals. Adder meets the female snake again much later and she tells him that she would like to be known as Sinuous.
They sunbathe together and Sinuous tells him that the Beast may be living underground, and Adder heads off to tell Badger and Fox about this theory. After the Beast leaves the park Adder spends most of his time with Sinuous and is hardly seen at all by the other animals.
In the Path of the Storm[]
The following spring sees several births among the Farthing Wood community, including baby adders produced by Adder and Sinuous. Adder searches out Sinuous early in the spring and she warns him that the stream may be dangerous as all the animals seem to be avoiding it.
Adder appears at the meeting of elders to discuss the problem with Trey, but he decides not to join the other animals on their trip to the pond to show Trey that he cannot stop them from drinking there. Adder shows much more concern for the other animals than he had done previously, making a special effort to visit Badger when he thinks the old creature is dying and delaying going into hibernation until Badger has been found after leaving the park.
Battle for the Park[]
When the rats are discovered in White Deer Park, Adder and Sinuous attack them in their nests, but Bully and the other rats set up a trap to catch them. As Adder enters one of the nests he is grabbed by Brat and Spike and calls for Sinuous to save herself. Eventually Plucky comes to his rescue and ensures that Adder can escape by threatening to dig his way into the rats' nest.
When Sinuous is killed, Adder blames himself for her death and goes into hiding for a while, but when he hears the other animals looking for him he returns to the fold. During the final battle Adder pursues Spike and eventually kills him to avenge the death of Sinuous.
Sinuous were neither seen or mentioned, it is highly implied that they were born and raised by the snakes unseen.
Against Sora's Team[]
Adder and other villainous animals have it in for Skipper, Kowalski, Rico, and Private and attempted multiple plots to end them.