The largest snake that ever existed is Gigantophis garstini, which lived from 40 million years ago till as recently as 40,000 years in North Africa. This snake reached 11 m (33 feet) in length, was related to pythons and boa, and could eat animals the size of a wild boar.
The biggest current snake is green anaconda (Eunectes murinus) (photo 1) from northern South America. The largest individuals can reach 9 m (27 feet) and 220 kg (550 pounds). Some say it could reach 11 m (33 feet), but this has not been proven yet. Anaconda is a type of huge aquatic boa snake and can swallow even pigs and caymans (a type of alligators).
The tiger pythons (Python molurus) from southeastern Asia almost equals anacondas: they are confirmed to reach 8.22 m (25 feet) but are slightly "slimmer" than anacondas: 182 kg (455 pounds).
The reticulated python (P reticulatus) from the same area can be even a little longer, till 9,15 m (28 feet) but is slimmer than the tiger python, with 145 kg (363 pounds) at this weight.
These are snake "giants", but the smallest snake is the Vieille's blind snake (Rhinoleptus koniagui) from West Africa: it reaches just 10 cm (4 inch) (photo 2)!
All the previous snakes do not possess venom; they kill by the power of their grip.
But the longest venomous snake is king cobra (Ophiophagus hannah) from southern and southeast Asia. It can reach 5.5 m (17 feet) length (photo 3).
But king cobras are slender, they usually do not exceed 20 kg (44 pounds), that's why other venomous snakes like the bushmaster (Lachesis muta) from northern South America, which is a pit viper (thus, related to rattle snakes), even if reaching 3.65 m (11 feet), overcome the king cobra in weight.
The most powerful venom was found to be that belonging to the sea snakes from the Hydrophis genus, related to the cobra.
Interestingly, there is no victim reported to have been killed by any sea snake, as with all their powerful venom, are very difficult to provoke.
The most venomous land snake is the so called infamous taipan (Parademansia microlepidotus) (photo 4) from Australia, which reaches 2 m (7 feet) length and is related to the cobras.
One taipan produces over 40 grams of venom, which is 300 times more powerful than that of the rattlesnake and 20 times stronger that that of the Indian cobra.
Of a current number of about 2000 snake species, in fact, only about 400 species possess venom strong enough to harm humans, and even less kill them.
Thailand is the country with the biggest number of venomous snake species: from 179, 60 are venomous!