The palps are long, and the second head-piece (peristomium) is twice as long as the next segment.
In Apus, as the figure shows, there are four of these “antenna-like” palps or filaments on the first thoracic limb.
All the cephalic appendages are much reduced, the mandibles have no palps, and the maxillulae are vestigial.
The palps are really derived from part of the velar area of the larva.
The sucking portions of the maxillae are vestigial, but the palps are long and jointed.
The cephalothorax and palps are a little darker yellowish brown.
Color—Cephalothorax and palps, dark reddish brown; abdomen, lighter than cephalothorax; legs, pale yellow.
It will often patiently explore a large area, testing the surface with its palps as it goes, without any obvious reward.
On finding a female nest, they serenaded by tapping with their palps, and after some delay, tore open the web and entered.
The creature could, however, achieve a kind of whistle by rubbing its palps against its mandibles.