After you have finished collecting for the day, it is wise to go ahead and prepare the specimens to put in your collection. This means putting them on insect pins. Don't wait until the next day, because the insects may become dry and brittle, and parts of the insect may break off when you try to pin them.
You can begin pinning the insects after they have been in the killing jar for about 20 minutes. If you take them out of the killing jar too soon they may revive after you have pinned them.
Use special insect pins that can be bought through your county Extension agent or 4-H project leader. Gently run the pin through the thorax of the insect a little to the right of the midline of the body. The following illustration shows examples of the correct spot to insert the pin. Leave about 1/4-inch of the pin visible above the specimen. This will be enough of a handle to pick up the specimen without touching the insect. There will be enough room on the pin below the insect to add labels. Work carefully and try to get the insect level on the pin so it is not tipped from front to back or from side to side.
To properly pin butterflies and moths, follow these additional steps. Once the insect is pinned through the body, position the wings as shown with a spreading board (purchased from a supply store) or with two blocks of StyrofoamTM, each twice as long as the butterfly or moth and about the same height as the insect on the pin, placed on either side of the insect. The wings should be gently pulled into place with an insect pin placed behind a large wing vein. The back margins of the front wings should be perpendicular to the insect's body, with just a slight notch between the front and back wings. Narrow strips of paper placed over the wings will hold the wings in place (the strips of paper should be pinned to the spreading board as well). Depending on the moisture in the air, it may take up to a week for the wings to completely dry in place.
Examples of correct pinning methods for common insects: (the black spots show where the pins should go.)
Other illustrations of the correct & incorrect ways to pin an insect