| # | Original airdate | Title | Overview | Animal that was Number 1 |
| 1 | 30 June 2002 | Jumpers | The fastest, highest and best jumpers. | Flea |
| 2 | 30 June 2002 | Gluttons | The greediest eaters in the world. | Caterpillar |
| 3 | 7 July 2002 | Speed | The fastest animals on land, air and water. | Tiger beetle |
| 4 | 14 July 2002 | Births | Extreme reproduction in number of young, size and other factors. | Tapeworm |
| 5 | 21 July 2002 | Cheats | The ways animals trick one another. | Cuckoo |
| 6 | 28 July 2002 | Survivors | The animals who best survive extreme conditions. | Water bear |
| 7 | 18 August 2002 | Builders | The animal kingdom's most innovative construction engineers. | Termite |
| 8 | 25 August 2002 | Horrors | The animals that inspire the most terror in humans. | Parasitic worm |
| 9 | 1 September 2002 | Fighters | Warriors of the animal kingdom. | Ant |
| 10 | 27 October 2002 | Strength | Proportionally, the strongest animals in the world. | Rhinoceros beetle |
| 11 | 3 November 2002 | Biters | The deadliest, most prolific and most extreme bites. | Cookiecutter shark |
| 12 | 10 November 2002 | Thinkers | Geniuses in the animal kingdom. | Parrot |
| 13 | 17 November 2002 | Lovers | Most extreme courtship rituals. | Redback Spider |
| # | Original airdate | Title | Overview | Animal that was Number 1 |
| 27 | 3 August 2004 | Gross-Outs | The most disgusting behavior in the wild. | Fly |
| 28 | 10 August 2004 | Home Designers | The most extreme, unusual and innovative animal architects. | Termite |
| 29 | 7 September 2004 | Tough Babies | The strongest babies in the animal kingdom, with human comparisons. | Sand tiger shark |
| 30 | 14 September 2004 | Wild Partiers | How the most extreme partiers in the wild compare to human parties. | Christmas Island red crab |
| 31 | 21 September 2004 | Monster Myths | The reality behind some of the most feared animals in the world. | Wolf |
| - | 25 September 2004 | The Best of the Best | Retroactive examination of Number 1s from earlier episodes, with a countdown to the most extreme among them. | Cookiecutter shark |
| 32 | 12 October 2004 | Killer Cats | The most ferocious felines in the world. | House cat |
| 33 | 19 October 2004 | Battle of the Sexes | Males and females of animals in which the two sexes have very little in common with one another and are not always good for each other's health. | Whiptail lizard |
| 34 | 23 November 2004 | Big Mouths | Proportionally, the 10 largest mouths in the world. | Argentine horned frog |
| 35 | 30 November 2004 | Deadly Snakes | The most venomous, dangerous and prolific killer snakes. | Cobra |
| 36 | 14 December 2004 | Killers | The animals with the highest human kill counts. | Mosquito |
| 37 | 8 February 2005 | Bloodsuckers | Vampires in the animal kingdom. | Tick |
| 38 | 15 February 2005 | Super Sharks | The "highest tech" sharks in the ocean. | Hammerhead shark |
| 39 | 22 February 2005 | Poison | The deadliest chemical defenses. | Golden poison frog |
| 40 | 1 March 2005 | Super Dogs | The 10 dog breeds that have evolved the furthest from their wolf ancestor. | Chihuahua |
| 41 | 8 March 2005 | Global Conquerors | The most invasive animal species. | Cockroach |
| 42 | 15 March 2005 | Outrageous Flirts | The unusual ways that animals attract one another. | Elephant |
| 43 | 27 April 2005 | Athletes | The most athletic animals and their human equivalents. | Arctic tern |
| 44 | 4 May 2005 | Odd Couples | When two kinds unite: unexpected animal partnerships. | Greenland shark/Ommatokoita |
| 45 | 25 May 2005 | Movers | The animals that move the best with the fewest limbs for movement. | Scallop |
| 46 | 1 June 2005 | Troublemakers | The animals that cause the most trouble for humans just by doing what they do. | Termite |