Depending on the species, the two main taxa you would want to get familiar with are the Lepidoptera and the Diptera. With regards to the Lepidoptera, scales are often all that remains in faecal pellets and these are very hard to identify. From my own experience with Diptera, fragments in faecal pellets are often easily identifiable. I have found that Nematocera remains are straightforward to place into family but one would have to be well versed in separating the Mycetophilidae from other Sciaroidea families when faced with a tibia or the like. Having said this, bats often bite off wings and legs prior to ingestion of the body, presumably because of the lack of nutritious quality.

Sometimes you might find a wing with a nice "vena spuria"/false vein which is characteristic of the Syrphids. Other times you might be on the look out for a humped thorax of a Chironomid. Sometimes you will get down to a few very similar families however, with the Chironomids and Ceratopogonids often being grouped together as in Williams et al., (2011). In other instances, if you are faced with an antennal segment of a Tipulomorph, you might have to bunch Trichocerids with Tipulids as they are very similar. You could collect a reference collection of insects from the area you are doing your work in first and then cross compare.

Depending on the species, the two main taxa you would want to get familiar with are the Lepidoptera and the Diptera. With regards to the Lepidoptera, scales are often all that remains in faecal pellets and these are very hard to identify. From my own experience with Diptera, fragments in faecal pellets are often easily identifiable. I have found that Nematocera remains are straightforward to place into family but one would have to be well versed in separating the Mycetophilidae from other Sciaroidea families when faced with a tibia or the like. Having said this, bats often bite off wings and legs prior to ingestion of the body, presumably because of the lack of nutritious quality.

Sometimes you might find a wing with a nice "vena spuria"/false vein which is characteristic of the Syrphids. Other times you might be on the look out for a humped thorax of a Chironomid. Sometimes you will get down to a few very similar families however, with the Chironomids and Ceratopogonids often being grouped together as in Williams et al., (2011). In other instances, if you are faced with an antennal segment of a Tipulomorph, you might have to bunch Trichocerids with Tipulids as they are very similar. You could collect a reference collection of insects from the area you are doing your work in first and then cross compare.

Dull answer this but it does need saying

It dependes on your question?... (ducks head down to avoid the flying bricks)

making poo soup might tell you what you want to know but probably will not - with the number of biases which may affect your question being shared to a limited degree between direct remains ID, SIA and the better molecular methods.  Of these SIA and the various PCR approaches might either completely answer your questions (if they are specific), or provide the most robust 'best guess' we can make at the moment.  Key issues are gut residency, your belief that certain insects or insect types are 'constrained' to particular locations, the quality of your knowledge about the temporal dynamics of the prey types and species and the precision of prey ID you're after.  I'm generally not a fan of direct ID but I'm biased - I spent the first decade of my professional scientific life as an entomologist IDing insects, before being co-opted to a bat project and then becoming a bat scientist

More info on questions would help

james

Thank you both. One of my questions is how much of their diet is terrestrial vs. aquatic insects such as Chironomidae and Simuliidae, which is why Rob's report that Tipulomorpha fares pretty well is such good news to me! My concern with SIA/PCR is that I won't be able to get a feel for quantity of species eaten, I could only look for presence/absence. Is that true?

As far as quantiative measure of diet are concerned - my view is a bit jaundiced - I'm not sure any are great but I had picked up that some of the qPCR approaches had been used on bat poo with some apparent power - I might be mistaken - see work by Matt Zeale on barbasellus sp.

As far as those two diptera go - where I live in wet windy england, you can find chironomidae every where and not just associated explicitly with water - but you will find bat ecologists reaching for the generalisation that this family is mostly associated with water to mean that chironimids in poo = foraging over water because it gives them something to say.

embedded in this is the realisation that just because I might be able to iD an insect family in poo should not necessarily mean that I can draw any worthwhile inference from that information.

does your work probe the difference between preference and requirement?  They may happily fill their tummies with aquatic insects because these are easier to get, but survive fine on terrestiral whenever aquatic disappear - its commong for diet studies to show species feeding in approximate proportion to what is available (with the obvious exception of hyper-specialist feeders)

also are your bats roosting close to your water/terrestrial foraging grounds - differences in distance may translate to poo at roosts representing a rarefied sample of the nights foraging with some roosts hardly representing the mainly used foraging site

Some friends of mine Isobel Abbott and Conor Kelleher are well worth tracking down to answer further questions. I am by no means an expert on Bat ecology. I had a fascination with bats of the British isles for a time when I observed an interesting spike in certain Diptera families present in their pellets leading up to their overwintering period. Isobel explained considerably more to me about feeding behaviours and prey preferences after this observation.

From what I have read, some species may preferentially feed on Lepidoptera, others more on Coleoptera and more on Diptera. I am usure of how exclusive a diet might be, however, but would guess that it is very dependent on the species. There may be preferences for foraging sites that support their prey. Myotis daubentonii in the U.K. is predominantly an aquatic Diptera feeder. Both it and others focus hunting at freshwater foraging sites. M. daubentonii also tends to feed on the families you have mentioned. I have seen bats frequently exploiting the swarming leks of Chironomids and Anisopodids in a more terrestrial setting too. I gather there are other species that focus more on gleaning. I vaguely remember being told too that there is a correlation between the structure of bat wings and their method of hunting, something to look at?

With regards to your question on PCR only evaluating presence absence- that appears to be the case, yes. As far as I know (now I am really going out on a limb), relative proportions of species may be determined but it is very costly. I too am currently pondering the use of barcoding to at least shed some light on unidentifiable female Nematocera.