Earwigs feed at night and hide in moist, dark places during the day. You can trap them easily during the day by providing them with a damp, dark place to crawl into. Use a number of pieces of 12-inch lengths of old garden hose, or short lengths of bamboo, or a rolled newspaper; in all cases soak them in water so they are damp when placed in the garden. Make a trap by filling a flowerpot with damp crumpled paper; then turn it upside down, but keep it propped up with a stick. Earwigs will crawl into the newspaper.
Place the traps near damaged plants, or in mulched areas, among shrubs or similar habitats. Check your traps once a day to remove the insects you've caught, dropping them into a jar of soapy water to kill them.
Like slugs, earwigs are attracted to beer. Place some stale beer in small jars and set the jars on their sides. The earwigs will crawl right in.
The University of Vermont Extension Service has developed an effective trap for catching earwigs. Take two 3-inch-wide boards and cut four 1/4-inch grooves in them along their full length. Fasten the boards together with a strong rubber band, matching the grooves. Stand these traps in shrubbery, hedges, around trees, or near whatever plants are infested with earwigs. Check them daily and shake the insects into a pail of soapy water or water with a little oil poured on top.
Marianne in California has great success with putting an inch of soy sauce in the bottom of a cottage cheese container. She covers the soy sauce carefully with a thin film of vegetable oil. She has three or four ½ inch holes cut in the upper half of the container and she keeps the lid on to keep out the rain. She sets this trap in the problem area and earwigs climb in to their death. After a week she disposes of the contents and starts again.
Boric Acid Trap
Use one or more small cardboard boxes, such as those holding Christmas cards. Punch ¼ inch holes in the sides near the bottom and bait it with a small amount of oatmeal or bran laced with some boric acid. Place the box outside in the garden and lay a board on top to protect it from getting wet from the rain. The earwigs will eat the bait and eventually die; however it will take a week for them to die so be patient. For information about boric acid products go to Yardener's Tool Shed and check out the Boric Acid Products files.
Attract Natural Enemies
While toads and lizards love to eat earwigs, the European earwig has at least two specific natural insect enemies in the U.S., a tachinid fly (Bigonicheta spinipennis) that was imported in the Northwest in 1924 and the parasitic fly Digonichaeta setipennis. In good years these parasites attack and kill over 1/3 of the earwig population. These flies look very much like common house flies, perhaps a tiny bit larger.
You can attract these flies by planting the following plants near the area where the earwigs have been a problem in the past.
Anise (Pimpinella anisum)
Buckwheat (Fagopyrum esculentum)
Coreopsis (Coreopsis tinctoria)
Cosmos (Cosmos bipinnatus)
Dill (Anethum graveolens)
Fennel (Foeniculum vulgare)
Golden marguerite (Anthemis tinctoria)
Painted daisy (Chrysanthemum coccineum)
Tansy (Tanacetum vulgare)