At the end of silk collecting five randomly selected spiders per treatment and species were sacrificed by lethal exposure to CO2and their major ampullate glands dissected as described by Jeffrey et al. . The glands and a sample of the remaining abdomen were immediately lysed with RNase free mini pestles in QIAzol Lysis Reagent and mRNA extracted using an RNeasy Plus Universal RNA extraction kit (Qiagen, Düsseldorf, Germany). In order to prevent any DNA contamination we used a gDNA Eliminator Solution provided with the extraction kit to remove all genomic DNA. The extracted mRNA was eluted to 30–35 μl and we measured the concentration extracted using a NanoDrop 1000 Spectrophotometer (Thermo Fisher Scientific, Wilmington, DE, USA). A mean concentration of 1376.4 ± 239.04 ng/μl RNA was extracted from all samples and did not differ substantially between species. Mean absorbance ratios of the samples were 2.24 at 260/280 nm, and ranged between 1.86 and 2.38, and 1.97 at 260/230 nm and ranged between 1.22 and 2.27. Absorbance ratios in this range are considered acceptable as ‘pure’ for single stranded RNA .