Noob Demoman
Scrumpy Noobus
Status: Very Common
These are the most common of all the species of Demoman, despite being ridiculously daft. They always aim directly for their enemy, unaware that their grenades fly in an arch. Because of this, they often just use stickybomb traps to (hopefully) kill their prey. This is rarely fruitful, as they are poor at laying traps, and thus are easily avoided. They can be annoying to enemies because of their stubborn habit of obviously lacing the base entrances with stickies, thus forcing them to take a longer route, increasing their possibility of dying. They are also cruel and humorless, endlessly harassing weaker foes, especially Noob Medics, their natural prey. Spies can easily kill them, so they won't stay an obstacle long.

DemoNester
Scrumpy Baitboi
Status: Somewhat Common
Coexisting among nests of Engineer, the DemoNester gives extra protection to the nest in exchange for ammunition and health. They lay traps of sticky bombs on the Intel or entrances to provide safety for any distracted Engies repairing their builds. They are quite friendly, and in their spare time they enjoy group taunts such as the Conga or high-five. There is also a subspecies that prowls through the enemy base, known as the Demosite.
Demosite
Scrumpy Baitboi Parasiticus
Status:Somewhat Uncommon
These crafty Demomen slink about the enemy base, littering it with traps to kill its prey. They are known to work with other parasites, especially Engies.

Sticky Jumper
Scrumpy Kahboomus
Status: Somewhat Common
This creature branched off of the Noob Demo ages ago, when the Sticky Jumper was introduced. They are paranoid about their health, so they know every location that has medkits. They also prefer to stay away from direct fights, preferring to pick off foes from the shadows, or find an alternate route into the enemy base. Like most Demomen, the Sticky Jumper is very friendly and social towards teammates. Because of their harmless bombs, they love to have contests to see who can launch themselves the highest or farthest.

Demoknight
Scrumpy Chivalrous
Status: Uncommon
These noble creatures are wildly successful in the fact that, instead of focusing on bombs, they prefer to charge headfirst into battle. It takes ages to perfectly master the process of charging into your foe and decapitating them. Because of this, few Demoknights make it to their second match. Despite this, Demoknights can be found in almost every gamemode. They come in several varieties, and subspecies aren't uncommon, such as the Sloth Demoknight, and the Kamikaze Demoknight.
Sloth Demoknight
Scrumpy Chivalrous Slowasasnailus
Status: Somewhat Rare
These guys are basically just a normal Demo with a sword, and no charge ability. Thought to be an early ancestor of every modern Demoknight, they still succeed, but have been pushed into trade servers and KotH servers, where they succeed better than their more dangerous cousins.
Kamikaze Demoknight
Scrumpy Chivalrous Kamikaze
Status: Somewhat Uncommon
This subspecies of Demoknight is self explanatory. They charge into an enemy base without stopping for medkits or to avoid danger. Their only goal is to cut down as many enemies as possible before they die. This leaves less challenge for their teammates to deal with, so as thanks, many Kamikaze Demoknights are accompanied by a Medic to increase efficiency.

Sticky Glider
Scrumpy Avius
Status: Rare
This is one of the more unusual species of demoman, and one of the few TF2 species capable of any form of flight. However, this isn't powered flight, as the Sticky Glider needs to launch itself into the air in order to glide across the map. It shares this ability with a species of Soldier, the Rocket glider. I don't know very much about this species aside from the fact that they can be easy to deal with. A raining barrage of bombs is bad unless a sniper, the natural predator of this species, can pick them off from higher ground.They are crafty and difficult to spot, but they glide too slowly to escape most of their predators.

Caber Bull
Scrumpy Ebrioseritus
Status: Endangered
The Caber Bull is a very rare species of Demoman that is very brave in battle. They wield the highly explosive Caber Toss, which is usually a dangerous weapon on it's own, as well as the ability to charge, surprising foes long enough to blow them up. Their attack plans are simple, charge at an enemy and blow them up. This makes them a bit innacurate, aside from the most strategic (If you can call them that) Caber Bulls. They are a perfect example of convergent evolution(when two species evolve similar biological components despite being unrelated) in the fact that even though the Caber Bull isn't related to the Demoknight, it still developed the ability to charge. Sadly, because of their risky method of hunting, as well as being in competiton with the far more succesful cousin the Demoknight, this species is starting to go extinct.

- Fun fact: The species name for the Caber Bull comes from the Latin terms Eritus and Ebriosus, meaning Angry and Drunkard respectively.