Heterometrus cyaneus (Vietnam) were obtained from the Pet Factory (Hülsede, Germany); all other scorpions tested in this study were collected during field trips and released following second venom extraction. For electrical stimulation of the membrane anterior to the telson, we used the transcutaneous electrical nerve stimulation unit Promed tens 1000 s (Promed GmbH, Farchant, Germany) connected with modified tweezers to apply power. To improve stimulation, the tweezers were lubricated with conduct gel. The intensity of stimulation current was adjusted for each scorpion; usually a pulse width from 200 to 250 μs and a pulse rate of 60–130 Hz was applied. The extracted venom was collected with a glass capillary (inner diameter of 1 mm; Hilgenberg GmbH, Malsfeld, Germany) that was attached to a flexible silicone tube and a disposable syringe, and transferred into a 0.5 ml Eppendorf microtube containing 200 μl of 35% ethanol/0.1 TFA.