When I see an unknown bug on my plants, I Google "common (plant name here) pests" and then go to the images tab and find something that matches. If that fails or I find it somewhere other than my plants, I either post a thread about it with pictures in the pests and diseases forum or I just Google the features of the insect. Different bug 'families' are identified by different things but it's not hard to get the hang of it.

EDIT: Hah, it messed up part of my post because I used the >

This post was edited by IAmSupernova on Wed, May 1, 13 at 18:29

Good advice above. You can also narrow down possibilities by crop - "common bean pests", "common squash pests", etc. and use the images tab. With some time and research you can quickly learn about the bad guys.

Normally it is the damage we note first rather than the actual bug so also noting the type of damage done - tiny holes, big holes, chewed edges, wilting, shape of leaves (rolled up, turned under, etc) will help narrow it down.

How much damage indicates if it is just a few pests that can be hand picked or many that need pesticide intervention.

And since many pests are regional, don't forget all the resources from your local county extension office. They are good at narrowing down pests specific to your area.

Dave

Here is a link that might be useful: Insect IDs (note all categories listed on left)

I guess I am old fashioned, because I have a few print resources I rely on, listed below. Plus, most garden books I have read give you a heads up of what pests to look for, so for example, I've always checked my tomatoes for hornworms, etc.
The Organic Gardener's Handbook of Natural Insect and Disease Control: A Complete Problem-Solving Guide to Keeping Your Garden and Yard Healthy Without Chemicals

What's Wrong With My Vegetable Garden?: 100% Organic Solutions for All Your Vegetables, from Artichokes to Zucchini

Don't have this but it looks good: Good Bug Bad Bug: Who's Who, What They Do, and How to Manage Them Organically

I learned my bugs with an Audobon Society field guide, back in the day. Once you know the bug, finding out whether it is good, bad, or neutral is simple enough. There are plenty of online resources, but they can be tricky to navigate if you don't know a little something about bugs. Unless you find you enjoy learning what different bugs are for its own sake, the method of just learning what the pests look like is probably easier.

I don't spend much of my time learning about bugs. Since I am not using any toxic spray I am not hurting any body. I used surround and it works. once I bought ladybug eggs and released the babies in the garden. I don't know if it did any good. The only problem with surround is when it rains you have to spray again. The only one I worry about are the honey bees they fascinate me and I watch them working for hours. They are very picky to select the most beautiful flowers. They were working on my Blueberry flowers but when the orange and tangerine and the peach flowered they abandoned the Blueberry. Hay you can not fight City Hall.

another resource is a publication from the University of California.
" Natural Enemies Handbook"
publication # 3386

Available at your local bookseller or likely at the library or inter-library loan.

Wolverine, you are also welcome to post pictures here. Very few go unidentified, unless the image is terrible.