Several meters below the bottom of the canopy is the understory, a layer made up of young trees, short species of trees, shrubs, and soft-stemmed plants. The understory varies a lot from rainforest to rainforest. But everywhere it is darker, there is less wind, and it is more humid than the canopy above it.
Many familiar houseplants are native to his part of the rainforest (philodendrons, zebra plants, and prayer plants, for example). These plants can thrive in your living room as well as the understory because both places are low-light environments.
Understory plants have to find ways to advertise their flowers, so that the animals and insects that carry their pollen, can find them in the dim light. Often these flowers are large and pale so they can be easily seen. Frequently, flowers grow directly on the trunks of trees (which is never seen in temperate trees), making them easier to find than if they were tucked away among the leaves. Understory blossoms also often advertise themselves by producing a strong smell suited to the particular tastes of the pollinator the plants depend on. Flowers pollinated by hawkmoths, for example, have a heavy, sweet fragrance, while those pollinated by bats have a meaty, sweaty odor.
In this dim, leafy world with its poor visibility, disguises can be very effective and are often used. An insect may look like a stick or a leaf, a poisonous animal or a bird dropping... As long it is unnoticed or is considered dangerous or inedible, it will probably be safe.
Most reptiles living in the rainforest understory are camouflaged to some degree, as protection from predators like coatis or eagles. Many tree snakes, like the emerald tree boa, are bright green to blend in with the foliage (while the ground level relatives are brownish to match the dead leaves on the forest floor).
This helps a snake avoid being eaten. It also helps it catch the food it eats. A camouflaged snake is almost invisible as it lurks, until its prey passes by, and in a flash it strikes.
Mammals, too, often have markings that blend into the understory foliage. A jaguar is hard to see as it waits high on a branch to drop onto the back of passing prey; its spots make it look like just one more variation in the dappled leaf light.
But the understory space is not completely filled with leaves and branches. Bats, birds, and insects can frequently fly more freely over longer distances down here than they can in the canopy above... so animals that eat these fliers are attracted to this part of the rainforest. Spiders, for example, stretch their webs across flight paths, catching insects and sometimes even bats and birds.
The humidity of the understory suits amphibians like salamanders and frogs. They cannot survive if their skin dries out, and most species must lay their eggs in water or on leaves over water. Once the eggs laid on the leaves hatch, the young fall to the pond below. Tree frogs have evolved feet with tiny suction pads covered with a sticky mucus that helps them hold onto branches. They move easily up and down rainforest tree trunks, usually under cover of darkness, to escape their predators.