Blackarachnia is a recurring antagonist on the show Transformers: Animated. She is based on her counterpart in Beast Wars.
Blackarachnia was once an Autobot named Elita One. However, when searching for a Decepticon warship with Optimus Prime and Sentinel Prime, they were attacked by alien spiders. Elita One tried to escape the spider cave, but fell back in. Optimus and Sentinel in a bad situation try to choose whether to save her or quickly abandon her. Optimus chose to leave her behind, and when Elita One tried to use her organic-matter downloading powers on the spider aliens, she infected herself with spider DNA and became Blackarachnia. Angered at Optimus for her reasons, she chose to become a Decepticon instead. She came back in the episode "Megatron Rising Part 1" where Decepticons Blitzwing and Lugnut's mission persuades her to catch the All Spark-powered key again from Sari Sumdac. Blackarachnia then tells of how she wishes to be normal again, but then Sari escaped from her with the help of Ratchet piloting the ship Teletraan 1.
She steals a key that contains the All Spark power from human/robot hybrid Sari Sumdac and uses it to drain organic power. But she forgets that spiders are also animal life, which starts to affect Blackarachnia as well, so Optimus quickly removes it. Afterwards, she hires a mutant person named Meltdown made of toxic melting material to remove her spider parts, with the help of Autobot Dinobots Grimlock, Swoop, and Snarl. However, Meltdown wanted to actually remove her robotic parts from the spider body to make a transforming animal. Blackarachnia tries to escape but couldn't, then Optimus Prime again came back in and stopped Meltdown. She escapes again.
Blackarachnia came back the last time in "Predacons Rising". She captures Wasp, an accused Transformer who was removed from the Elite Guard when Wasp was framed by Decepticon Shockwave. Blackarachnia has the Dinobots guard her lair when Sentinel Prime and his allies Jetfire and Jetstorm distracted the Dinobots. Sentinel then meets Blackarachnia, who she tells of her past. Sentinel, realizing this, tries to confess that Optimus was the one responsible for her misfortunate fate of becoming a Transformer/spider hybrid, and the Supreme Commander of Autobots, Ultra Magnus, forbidden Sentinel and Optimus from coming back to the planet where Blackarachnia turned into what she is. Optimus came in, but just until Wasp was also infected as a transforming arachnid hybrid just like her. Wasp later renamed himself Waspinator and attacks Sentinel and Autobot Bumblebee. The lair detonates, and Waspinator and Blackarachnia land in an island full of animals (the same type of the original four Maximals from Beast Wars). Blackarachnia sees the animals, responding "Oh, you have got to be kidding me".