This is an ability that automatically happens when you do a saving throw, you have to roll a d20 for this and if you get an 11 or higher it sprays your enemies poisoning them and disorienting them, if its 10 or lower you accidentally spray yourself disorienting yourself.

The web shot ability allows the user to shoot a strand of web from either the mouth or abdomen, they can also alter the length and width of the web at will. The longer you want to make it the higher the role has to be, to use this you have to roll a d20. Nat 20 roll will allow the max length of 60ft to be reached, if a Nat 1 is rolled the web can't go further than 5ft.

This is an extra action that can be used which allows them to alter whether they have 8 legs, 6 legs 2 arms, 4 legs 4 arms, etc. most stick with the usual 6 legs 2 arms since that is how they move the fastest. the abdomen of the arachnidian can not be removed at all, not without a spell or wanting a death wish at least.