Not so dangerous after all? Venom composition and potency of the pholcid (daddy long-leg) spider Physocyclus mexicanus

Abstract Pholcid spiders(Araneae: Pholcidae), officially “cellar spiders” but popularly known as “daddy long-legs”, are renown for the potential of deadly toxic venom, even though venomcomposition and potency has never formally been studied. Here we detail the venomcomposition of male Physocyclusmexicanus using proteomic analyses and venom-gland transcriptomes (“ venomics”). We also analyze the venom’s potency on insects, and synthesize available evidence regarding mammalian toxicity. The majority of the venom(51% of unique polypeptides and 68% of tryptic peptides) consists of proteins homologous to known venomtoxins including enzymes ( astacinmetalloproteases, serine proteases and metalloendopeptidases, particularly neprilysins) and venompeptide neurotoxins. We identify 17 new groups of peptides (U1-17-PHTX) most of which are homologs of known venompeptides and are predicted to have an inhibitor cysteine knot fold; of these, 13 are confirmed in the proteome. Neprilysins(M13 peptidases), and astacins(M12 peptidases) are the most abundant venomproteins, respectively representing 15% and 11% of the individual proteins and 32% and 20% of the tryptic peptides detected in crude venom. Comparative evidence suggests that the neprilysingene family is expressed in venomsacross a range of spidertaxa, but has undergone an expansion in the venomsof pholcids and may play a central functional role in these spiders. Bioassays on cricketsresulted in an effective paralytic dose of 3.9 µg/g, which is comparable to that of crude venomsof Plectreurys tristisand other Synspermiata taxa. However, cricketsexhibit flaccid paralysisand regions of darkening that are not observed after P. tristis envenomation. Documented bites on humans make clear that while these spiderscan bite, the typical result is a mild sting with no long-lasting effects. Together, the evidence we present indicates pholcid venomsare a source of interesting new peptides and proteins, and effects of bites on humans and other mammals are inconsequential.