We used published C-terminal domain sequences for MaSp1 and MaSp2 from Argiope trifasciata (hereon called MaSp1a and MaSp2a) and Latrodectus hesperus (hereon called MaSp1b and MaSp2b) [7,68–71] to order primers for the RT-PCR analyses (see Supporting Information, S1 Table for sequences and accession numbers) using the Fluidigm online assay designer . We converted the threshold cycle (CT) values (see S2 Table) derived by the RT-PCR analyses to 2-ΔΔCT values, which were averaged for each individual spider across the three technical replicates, following Schmittgen and Livak .