Topic: Spitting in spiders and velvet worms
Scytodid spiders forcibly eject a mixture of saliva, silk and venom in a glutinous mass over a distance of c. 1cm to entrap prey.
Many animals produce an initial secretion to lubricate food ingestion, and begin digestion. Such saliva production is widespread, and no doubt has evolved several times. There are, however, other examples of forcible ejection of saliva in order to trap prey, best knownin scytodid spiders but also found in velvet worms (onychophorans).
Scytodid spider spitting
The scytodid spiders can forcibly eject a mixture of saliva, silk and venom in a glutinous mass over a distance of c. 1cm to entrap prey. Typically they hunt salticid spiders, and can spit a number of times, if necessary. Once immobilized then the spider bites its prey. Although the scytoid builds a silk web, this is not used to trap prey but is employed as a nest and may act as a tripwire.
Velvet worm slime
The second example is not strictly spitting, but involves the forcible discharge of sticky slime from the oral papillax of velvet worms (onychophorans). The squirting is very rapid indeed and the adhesive threads act in very much the same way as silk and even have adhesive droplets. It is not, however, a true silk, but seems to have a collagen-like composition. Once trapped, and the velvet worms are nocturnal hunters, the prey is then bitten and death rapidly ensues.
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Map of Life - "Spitting in spiders and velvet worms"
December 9, 2018