Venom composition of the scorpion Chactas exsul (Scorpiones: Chactidae) from the premontane tropical rainforest of Costa Rica.

Chactas exsul (Werner, 1939) is a specialized, saproxylic scorpion belonging to the diverse family Chactidae, inhabiting the humid tropical forests of Costa Rica and Panama. Characterized by robust pedipalps and a relatively small telson, C. exsul primarily relies on mechanical immobilization for prey capture, though it may utilize venom during challenging encounters. Despite its evolutionary importance, the venom of most of its members remains largely uncharacterized. In this study, we provide a comprehensive proteomic and biochemical analysis of the venom of C. exsul from the Caribbean lowlands of Costa Rica. Our results reveal a venom peptidome dominated by putative scorpine-like antimicrobial peptides, calcins, and orphan components such as La1-like peptides. Sodium channel-modulating toxins (NaTxs) and common non-buthid potassium toxins (α- and κ-KTx) were not identified. The protein fraction exhibited significant complexity, featuring metalloproteinases, serine proteinases, phospholipases A2, and two putative hyaluronidase isoforms, among others. CAP-domain secretory proteins show several variants in the venom. These findings suggest a dual-functional trophic and, probably, defensive strategy: with a peptide fraction likely targeting insect-specific K+ and Ca2+ channels, which could induce paralysis, while the enzymatic cocktail could facilitate toxin maturation and spreading, as well as tissue predigestion. These activities and the role of putative scorpines as antimicrobials against soilborne pathogens inhabiting humid microhabitats remain to be determined.