"Camel spiders have evolved a unique way to capture their insect prey.
"The arachnids catch insects by sticking to them, using adhesive patches on the ends of their pedipalps, tube-like organs on either side of their mouth…
"Some camel spiders are known to be able to use these organs to stick to, and climb, vertical surfaces such as walls, although it is unlikely they climb much in the wild, where they tend to cover sand and prefer to hide under rocks.
"Anecdotal observations have also suggested that they strike at or try to grasp prey with their mouthparts, but the action happens too fast to be certain about how they capture their victims.
"So Dr Rodrigo Willemart of the University of Nebraska in Lincoln, US and colleagues based in Ireland and the UK decided to use high speed video to record the action." (Walker 2010)Edit Summary
"…although named for a presumed suctorial function, recent morphological studies suggest that surface features, and the lack of glandular openings, indicate that dry adhesive mechanisms, for example van der Waals forces, predominate…
"In summary, the suctorial organs of solifugids serve an important function as the primary means of capturing fast, mobile prey items. Future study of variation in grasping organs across arachnid groups, and variation in their ecological function, may not only enable an understanding of their evolutionary history, but might one day help in the design of bio-inspired grasping devices." (Willemart et al. 2010)
Note: These organs serve multiple functions: prey capture, defense, bringing water to mouth for drinking, climbing on smooth surfaces, and locomoting on slippery surfaces.