Probable sodium channel pore blocker that dose-dependently inhibits voltage-gated sodium channels (VGSC) on DUM neurons in a way similar to tetrodotoxin (PubMed:20506577). Has no effect on the kinetics of activation and inactivation (PubMed:20506577). Seems not to interact with VGSC in an inactivated state (PubMed:20506577). In vivo, reversibly paralyzes cockroaches, and can enhance the muscular contraction elicited by stimulating its nerve (PubMed:14614533). Expressed by the venom gland. The presence of a 'disulfide through disulfide knot' structurally defines this protein as a knottin. The natural mutant mHwTx-III does not reversibly paralyze cockroaches. PD(50) of HwTx-III is 192.95 +/- 120.84 mg/kg to locusts. Does not inhibit sodium channels of adult rat DRG neurons (PubMed:20506577). Neither HwTx-III, nor mHwTx-III agglutinate erythrocytes (PubMed:14614533). Belongs to the neurotoxin 10 (Hwtx-1) family. 51 (Hntx-8) subfamily. Hntx-8 sub-subfamily.