One of the great ironies of biology is that biologists spend a fair amount of their time killing the organisms that they study. Don't get me wrong, I'm not saying that collecting doesn't have it's place, but we must recognize it for what it is. Having said this, I should also note that most biologists avoid destructive collection whenever the objectives of their studies can be met in other ways; or if the populations of the organisms in question are vulnerable.
In the case of spider study, collecting is still relatively frequent.
There are two reasons for this. First, with the exception of a few large or
distinctive species, most spiders cannot be identified without microscopic
examination. Serious study of an organism usually begins with
identification. Second, because of their relatively small size and high
reproductive capacity, most spiders have high populations in suitable habitat.
There are frequently hundreds to thousands of individuals per hectare. For
those species, removal of a few individuals is unlikely to adversely affect the
health of the population. Above all, think before you collect. Is it
really necessary to kill the specimens? If so, are you prepared to take
the basic data and label the specimens so that they are useful as permanent
records?
to Permits
to Fluids for Preserving Spider Specimens