Aside from the main English-speaking countries of the West (UK, USA, Australia),
which countries can boast the most detailed taxonomic work on their own insects/spiders so far?
The reason why I ask is that I treat my wildlife list rather like my birding list, in the sense that I can only “tick” something if it has been positively identified to its species. It would be nice to visit a country on holiday, where I can “tick off” a great number of insects/spiders without having to place the records at the level of genera or families.
I live in Hong Kong, for instance, and it is clear from the suggested IDs for my observations that much is still not known about the taxonomy of many local spiders. To the credit of entomologists here, almost all species of butterflies and dragonflies in Hong Kong are known.
Spiders often need genitals to be ided, so ids you get is not the sign of taxonomy details (but yeah, tropical Asia gets newly described species all the time), worldwide you would need specimens or at least move them around to get species id on all, but some charismatic species of spiders.
Can’t speak for spiders, but for Insects the DACH countries (Germany, Austria & Switzerland) have a formidably detailed literature. The standard work on Swiss bees runs to 6 volumes, that for Beetles, Die Käfer Mitteleuropas, ran to 15 volumes plus supplementary ones on larvae and ecology. Many regions of Germany produce specialist books on their local fauna which are often very useful for people living elsewhere, a good selection on beetles is illustrated here. There is furthermore a long tradition of such detailed works: earlier standard works can be found at the Biodiversity Heritage Library.
France and Spain produce some nice works in their major series: Faune de France and Fauna Iberica, once again often being generally useful across the continent.
Britain does less well with detailed monographs of particular groups: one on Beetles is in progress, the one on Bees took a long time to appear, and the Lepidoptera one ran out of steam (and is also very expensive). However, there are good more popular books covering many groups, a volume on Spiders (the Collins guide) sold in phenomenal numbers. Of the major Insect orders Diptera & Hymenoptera have the worst coverage, but this is probably true everywhere: some economically important families of flies perhaps have less than 10 people worldwide dealing with their taxonomy, and often identification requires microscopes and preparation equipment. It’s still perfectly possible to find new species in all these countries: this for instance was first described in 2003, and the keen macrophotographers of springtails found a few new species.
The other big problem everywhere is taxonomic change, and in many insect groups the realisation that a single species is actually a complex of cryptospecies.
In summary most countries in Western Europe have pretty good taxonomic coverage of Arthropod groups, but in part because gaps in the literature are often covered by work from a nearby country with many of the same species.