You can catch most tachinids using a standard butterfly net – either round or kite-shaped, depending on your own preference. An extendible handle is useful for reaching flowers that are hard to get at and I count my telescopic handle is an expensive but essential part of my field kit. This method will yield quite a large range of species once you learn to spot tachinid behaviour and appearance in the field, and it has the added advantage that you get to see the insects behaving naturally and this can give you interesting and valuable additional data. However, this method can be a bit laborious and often only yields the larger, obvious species that sit out in the open on flowers.
Another good method is to ‘sweep’ low vegetation and flowers using a large canvas net – this gets all those small species that lurk i nthe undergrowth. But it can be quite exhausting work on a hot day and crashing through vegetation is sometimes frowned upon on nature reserves!
Probably the best way of seeing a good cross-section is to put out a Malaise trap – for more info see my Malaise trapping primer. Tachinidae usually form only a small proportion of the catch but you get a lot of insects and the catch is not biased towards any particular group.