Like in the real world, many people of the Tackleverse like to formulate speculations about the existence of extraterrestrial lifeforms, and how they might look like. Among them are Shelley Winters  and Charlotte Grote . The latter even wrote a poem about aliens invading Earth , which won her a trip to SpaceUK.
It has been shown on several occasions though, that there are indeed aliens in the Tackleverse. These include:
- Xaktar and Gimblaar , the two aliens who visited Shelley Winters one night. They were looking like Greys, whom both Shelley herself and Lottie were later mentioning in their speculations about different alien species. Instead of "their probing ways" though, they merely wanted Shelley to help them repairing their spaceship. On the other hand, one thing Shelley more accurately remembered about them was their language.
- J'hx'tharblath, who emerged from Shelley and Fallon's refrigerator (perhaps through one of the many space, time, and dimensional warps which tend to show up in the Tackleford universe), and beat Shelley at Scrabble by using seven-letter alien-language words.
- Space Owl, who was, as the name suggest, a (giant green) owl from space, and thus an alien lifeform. Rachel Dukakis-Monteforte and Tessa Davies helped him to win the 2005 election in Wales.
- The aliens from planet Korfus. They were humanoid, tall, blue, and possessed highly advanced technology. Around 1955, they destroyed their own planet in the "Battle Of Whose Turn Is It". Luckily, some of them survived because they were on a diplomatic mission to Earth, but unluckily, most of them were killed by the wife of an onion farmer upon whose house their spacecraft crash-landed on. Only two survived, too few to repair their spacecraft on their own. So they used their technology to grow children out of onions. Of these, only Lem was resembling a human being, and he was sent out to attend Griswald's Grammar School, in order to recruit helping human hands.
- The alien associated with Ben Bishop. The CEO of Zambian Computing was once presenting a small crab-like alien (allegedly found in Earth's upper atmosphere) to the board of his company, while talking about a "new alliance" and a "new dawn". John Allison stated in the annotation that this alien was a reference to the ones appearing in a "classic TV show episode". This and other circumstantial evidence (Ben crying black tears, as well as him and the alien emitting very similar sounds when in agony) seem to suggest that Ben's body was actually possessed and controlled by another specimen of this alien lifeform, and that he planned to use the one shown to the the board members to infect them likewise. If this was indeed the case, this plan luckily got thwarted by Jordan P., who accidentally killed the alien by spilling a taurine containing energy drink over it.