rhamphotheca:

entomolog: Arolium, Empodium, Pulvilli

The tarsus of insects usually consists of several small joints, the last of which generally carries a pair of terminal claws. The last tarsal segment may be extended between the claws to form a pad-like organ - the arolium. Some Diptera (true flies) have two additional pads - the pulvilli (singular: pulvillus) - lying below the claws on either side of the arolium , although in most flies, including the common housefly and its relatives, the arolium is replaced by a stout central bristle - the empodium. In many insects, the other tarsal segments also have ventral pulvillus-like organs, called plantulae. These various structures - the arolium, pulvilli and plantulae - produce a sticky secretion and act like ‘suction-pads’, enabling the insect to climb smooth or steep surfaces. This is the secret of the fly’s ability to walk up-side-down on the ceiling!

Fact Source: http://www.kendalluk.com/morph.htm

Figure: Encyclopedia of Entomology, John L. Capinera , 2008

SEM (Scanning Electron Microscope) Photo 1: Foot of a Weaver Ant (Oecophylla smaragdina) worker. Pretarsal claws and manubrium in red; arolium in yellow; tarsi in green (Scanning Electron Micrograph, Roberto Keller/AMNH)

SEM (Scanning Electron Microscope) Photo 2: . The hairy adhesive pads, or pulvilli (beneath the claws), allow the Stable fly (Stomoxys calcitrans) to cling to smooth surfaces.

SEM (Scanning Electron Microscope) Photo 3: The Figeater Beetle’s (Cotinis mutabilis) leg is comprised of a variable number of segments, incliuding the pretarsus, seen here with a claw and spiked empodium.