Selectively slows channel inactivation of mammalian Nav1.1/SCN1A, Nav1.3/SCN3A, and Nav1.6/SCN8A and shows higher affinity for insect Nav1/para channels (site 3). Induces tonic repetitive firing of nerve impulses in insect neurons accompanied by plateau potentials. Expressed by the venom gland. The presence of a 'disulfide through disulfide knot' structurally defines this protein as a knottin. LD(50) 0.15 pmol/g by intracranial injection into mice. LD(50) is 1.2 nmol/kg in lepidopteran larvae. Belongs to the neurotoxin 06 (delta-actx) family.