Hipposideros diadema is named for its complex anterior nose leaf, which is horseshoe-shaped and located on the slightly inflated nasal region.

[5] Males have a sac located posterior to the nose which can secrete a waxy substance, thought to be used in attracting mates and status determination.

Body length ranges from six to ten centimeters when adult, with brown fur covering all but the limbs.

[7] The oral region of the skull exhibits premaxillary palatal branches that are fused medially, and widely separated from the maxillae laterally.

With a heavy body and long, narrow wings, the Hipposideros diadema is adept at fast flight but has relatively poor maneuvering ability.

This bat species is not restricted to rain-forest and in outback Australia it forages within eucalypt woodland and open forest, deciduous vine thicket and within towns.

[4] The diet varies depending on specific location, but they tend to prefer insects such as coleopterans (beetles), lepidopterans (butterflies and moths), and those within the orthopteroid (grasshoppers) orders.

[11] Lepidopterans (eared moths) make up a significant portion of their diet and these insects have an auditory range from 20 to 50 kHz.

Research has shown that these insects can sense the echolocation pulses and have learned to evade or hide from the attacking bats.