With a hand lens and photo-illustrated guide by Oregon State University Extension and Oregon Tilth, you can teach yourself to identify beneficial insects that prey on crop pests.
The guide is called "A Pocket Guide: Common Natural Enemies of Crop and Garden Pests in the Pacific Northwest" (EC 1613-E). It includes macroscopic photos of many natural predators and parasitoids in their life stages, along with identification and observation tips.
It is available online for no charge at: http://ipmnet.org/Pocket_Guide_of_Natural_Enemies.pdf
The Farmscaping for Beneficials program at OSU's Integrated Plant Protection Center (IPPC) works with Pacific Northwest growers to help foster beneficial invertebrate predators and parasitoids and native pollinators on their farms. These tiny creatures can help control crop pests such as aphids, cutworms, earworms, slugs, leaf miners, spider mites and earwigs.
Many of the same strategies can apply in home gardens, thereby reducing the need for pesticides in yards and gardens, explained Gwendolyn Ellen, coordinator of OSU's Farmscaping project. Information is available online at: http://www.ipmnet.org/BeetleBank/Farmscaping_for_Beneficials.html
"Predators and parasitoids that can manage farm and garden pests include lady beetles, predator mites, hoverflies, the green lacewing, damsel bugs, stinkbugs, parasitic wasps and predacious ground beetles," Ellen said. "The trick is to learn to tell the good bugs from the bad."
Photos of beneficial insects also can be found at: http://mint.ippc.orst.edu/beneficialinsects.htm
Home gardeners can enhance habitat for native pollinators and lure them to the garden with plants. Cilantro, yarrow, wild buckwheat and white sweet clover attract natural predators of pests in Oregon. Tansy, sweet fennel, sweet alyssum, spearmint, Queen Anne's lace, hairy vetch, flowering buckwheat, crimson clover, cowpeas, common knotweed, caraway and black locusts also attract natural enemies of plant pests.
Cilantro and sweet alyssum are particularly effective in attracting hoverflies, whose larvae are voracious aphid predators.
For more information on how to bring pollinators to your garden, see http://extension.oregonstate.edu/gardening/node/1032.
Another OSU publication, "Encouraging Beneficial Insects in Your Garden," is available at http://extension.oregonstate.edu/catalog/abstract.php?seriesno=PNW+550.