A good field guide (right) is the
best reference source for non-specialists to identify an unknown
insect or spider. Field guides generally
have photographs, distribution maps and life
histories for the common species in a particular
area, organized in some logical grouping.
Field guides usually are written for a
particular region such as North America, or the
eastern US, or the western US, and so on. They can
also specialize in a particular insect group such as
beetles or butterflies.
In general, the more specific a field guide
is in terms of group and regional coverage the more
detailed the information will be, but this comes at
the expense of broad coverage. So, for example, a
field guide of the beetles of Oregon will contain
far more detail about the beetles of Oregon than
will a field guide about the insects of North
America. I like more narrowly focused books because
they give me the detailed coverage I need but they
can be more difficult to use until you are somewhat
familiar with the topic.
Field guides are highly individualized in
that what works for you may not work for someone
else. Each publisher and author has their own way of
organizing the same basic information so don't be
afraid to compare field guides until you find the
one that suits you.