The Backswamp is the interior of the swamp, which gets more pejorative as one gets closer to the Perdition. Here is where you begin to find monstrous spiders, centipedes, wasps, beetles, ants and bees. Huge vipers and giant constrictors slither the countryside, eating monstrous toads and giant frogs. Gargantuan alligators stalk dire deer, competing with the shocker lizards and voracious black bears for food. Large bats swoop and dart, eating giant mosquitoes. An elasmosaurus dinosaur indiscriminately crushes shrubs and trees in its path, but gives a wide birth to the black dragon residing within. Foul Frogs lie in wait for unsuspecting prey, their bodies hidden beneath the mud and water. Mudbugs await those who travel isolated bayous.

If visitors brave the dangerous beasts, the deep interior reveals horrors that are more sophisticated. Ettercaps create cunning traps ensuring the unwary never get a chance to draw their weapons. Mire giants can be found eating the flesh of aquatic grick and owlbear. Stirges are common here, as are spider eaters and an amphibious variety of krenshar. Shambling mounds rest on shallow water surfaces, disguised as vines and duckweed, while tendriculos await prey in known animal paths. Poison ivy assassin vines stretch down to grab their next victim. Hungry scrag trolls might be tracking Lizardfolk, or a will-o’-wisp may attempt to lead a party astray. After an aquatic ankheg discards the body of its latest victim, monstrous carrion eaters finish the meal. Treants may help protect the innocent, but in Dreadmire they are few and far between.

The Backswamp of Dreadmire is filled with abominations. Here is the lair of a black dragon, a nest of harpies, and the submerged cave of a medusa and a water naga. It is said aranea guard the home of a summoned hydra and that trained howlers are at the disposal of a gang of athach. Roaming packs of chuul avoid the purple worms and their staple food source, the gray renders. Gray oozes are somewhat common here, as are black puddings and ochre jellies. It is known that the fabled Goliath Pelican makes its home within the Backswamp, as do the evil Serpents. Although Giant Eagles keep watch from above and Giant Owls patrol below, it is seldom of any use. The evil presence is too pervasive there.

Travelers on foot can wade through the Backswamp at the rate of 5 miles in a day. By punting on a bateau boat, it is possible to move 12 miles per day, presuming 16 hours of travel and 8 hours of sleep. Rangers and druids know the intermittent animal paths over dry hummocks, increasing walking speed to 8 miles in a day if one accompanies a party.