[4][8] The saddleback toads live among leaf litter in the Atlantic rainforest, ranging from near sea level to an altitude of 1,900 m (6,200 ft), with most species restricted to highland cloud forest.

[9][10] They are mostly diurnal, feed on tiny invertebrates and breeding is by direct development, with eggs laid on land and hatching into young frogs (no tadpole stage).

[20] This makes them the smallest known frogs, with only the northeast Brazilian Adelophryne michelin, and Cuban Eleutherodactylus iberia and E. limbatus approaching their tiny dimensions.

[15][19][27] Two particularly dull-coloured species, B. brunneus and B. curupira, are overall brown,[18] while a few others are essentially all-brown or greenish above (sometimes with whitish on the mid-back), limiting yellow or orange to the underparts.

[30] At least two brightly coloured species, B. ephippium and B. pitanga, have bones that are fluorescent, which is visible through the skin of the toadlet when exposed to UV light.

[30] Peculiarly, at least the brightly coloured pumpkin toadlets B. ephippium and B. pitanga are unable to hear the frequency of their own advertising calls, as their ears are underdeveloped.

Instead their communication appears to rely on certain movements like the vocal sac that inflates when calling, mouth gaping and waving of their arms.

[30] Direct studies of the medium-brightly coloured (mostly dull above, bright below) pumpkin toadlet B. actaeus and the dull-coloured flea frog B. hermogenesi strongly suggest that they are able to hear their own calls.

[5][32] Saddleback toads live in the leaf litter on forest floors,[9] but on occasion may move to higher perches up to 1 m (3.3 ft) off the ground.

[12][15] However, whereas most frogs typically only use one technique, at least B. ephippium will use two, beginning with an inguinal amplexus (where the male holds the female around the lower waist, just in front of her hindlimbs) and only later changing to a nearly axillary position.

[12] Based on the few species where the breeding behavior is known, the female saddleback toad lays about five or less yellow or yellow-white eggs, which are relatively large compared to the size of the adult.

They are known to feed on insects (among others, ants, true bugs, beetles, grasshoppers and flies) and their larvae, springtails, mites, spiders, pseudoscorpions, millipedes, snails and isopods.

[37] Due to Brachycephalus' extremely small head and body size, vestibular systems in the genus are too small for dependable locomotion, and in turn the endolymph — which is regarded by Poiseuille's law — is not detected by sensory hairs and makes it difficult for individuals of Brachycephalus to sense changes in angular acceleration during a jump.

Because of the uncontrolled jumping and slow walking, they have evolved defense mechanisms such as toxicity and bony plates (osteoderms) as protection against predators.

[9] Two of the data deficient species, B. atelopoide and B. bufonoides, have not been recorded since their original scientific descriptions a century ago and they are unknown in life.

[9][43] The three flea frogs B. didactylus, B. hermogenesi and B. sulfuratus and the pumpkin toadlet B. ephippiumsi are relatively widespread in both distribution and altitude range (lowlands to about 1,100–1,250 m [3,610–4,100 ft]), although it is possible that the last of these actually is a species complex.

[9] These are typically in cloud forest on sky island mountaintops and most species have completely separate distribution, isolated from each other by valleys and unsuitable habitat.

[9][10] Some Brachycephalus species have also been found to be afflicted by recurrent outbreaks of Batrachochytrium dendrobatidis despite the fungus largely affecting aquatic frogs; these outbreaks have been linked to dry years where low water availability poses a physiological stress on frogs and also forces them to retreat to refugia where they are at a high population density.

[44] Brachycephalus lacks a Bidder's organ, but were historically included in the true toad family Bufonidae, where one of the defining features is its presence.

[45] The many recently discovered species have mostly been the result of scientists visiting isolated highland peaks, so-called sky islands that are separated from each other by valleys.

[15][49] Although now generally recognised,[45] the distinction of some of these recently described species has been questioned by some authorities since they often have been separated mainly by colour and skin texture, features that can be variable in frogs/toads.