It is imperative to obtain a representative sample of each population for population genetics studies. Furthermore, it must still be possible to isolate DNA from these organisms. We adapted the pitfall technique for that purpose after encountering severe problems collecting sufficiently large numbers of live Coelotes terrestris (Wider 1834) (Amaurobiidae) in the field. Although this species is commonly caught in pitfalls, collecting them by hand proved to be much more laborious than expected. Initially, we tested two types of live-traps (one cup and one funnel trap) which had been successfully used to catch carabid beetles. Both types did not yield enough captures of C. terrestris to get a representative sample of the studied populations. Therefore, we tested three different killing/preservative solutions (70 % ethanol, acetic acid TE buffer and 4% formaldehyde) for possible use in pitfall traps. Ethanol was the best preservative solution based on the amount of DNA that could be isolated after treatment and on the ability to generate the same RAPD profile as a reference DNA sample preserved at−20 °C. To test ethanol as a preservative solution in the field, we varied its concentration and used it in combination with traps with or without funnels. We conclude that it is best to use a funnel trap with 96% ethanol. We further recommend that for every new species to be sampled in this way an explorative investigation should be carried out determining where, when, and how many traps should be placed (this reduces the expense of the method). Furthermore, the effects of different preservative solutions on the DNA of an organism of interest should be tested. The resolution of the molecular analysis will determine if the DNA should be of high-molecular-weight or if some degree of denaturation is allowed.