Preserving bugs comes down to two broad approaches: dry mounting for hard-bodied insects like beetles, butterflies, and grasshoppers, and wet preservation in alcohol for soft-bodied specimens like larvae, caterpillars, and very tiny insects. The method you choose depends on the type of bug and how long you want it to last.
Killing Specimens Humanely
Before you can preserve a bug, you need to kill it quickly without damaging its body. The simplest method is freezing. Transfer the insect to a small bottle or box and place it in a household freezer for one to three hours. This is safe, requires no chemicals, and has a major advantage: you can leave specimens in the freezer for days or weeks without them drying out or decomposing, giving you time to mount them when you’re ready.
The traditional alternative is a killing jar made from a glass jar (not plastic) with about an inch of dried plaster of Paris in the bottom, saturated with ethyl acetate. The fumes knock insects out quickly. Keep the jar tightly capped when not in use, and always place crumpled paper towel or tissue inside to absorb moisture and prevent specimens from rattling around. Ethyl acetate is toxic, so label the jar clearly as poison and keep it away from children. Don’t leave insects in a killing jar for more than a day, or they’ll become too soft and fall apart.
Dry Pinning for Hard-Bodied Insects
Pinning is the standard preservation method for adult beetles, flies, bees, dragonflies, and most other hard-bodied insects. You’ll need entomological pins (regular sewing pins are too thick and will rust) and a pinning block, which helps you position specimens at a uniform height.
Pick up the insect by its midsection (the thorax) and push the pin straight through it from top to bottom, slightly to the right of the center line. Push the pin down through the insect until about a third of the pin remains above the body. This leaves enough pin above to handle without touching the specimen, and enough below to secure it in foam or a display box.
Timing matters. Insects taken out of a killing jar or freezer are still flexible, and that’s when you want to pin them. If they dry out before you get to them, their legs and antennae become brittle and will snap off. You have a window of a few hours after thawing or removal from a killing jar to position everything.
Spreading Wings on Butterflies and Moths
Butterflies and moths need their wings spread flat so both the upper and lower surfaces are visible. A spreading board is a flat surface with a central groove where the insect’s body rests while the wings are positioned on either side. You can buy one or make a simple version from balsa wood strips, paper clips, and common pins.
After pinning the butterfly through the thorax and placing it in the groove, use a mounting needle (not the pin itself) to carefully slide each wing forward into position. The trailing edge of the front wing should form a straight line perpendicular to the body. Once the wings are positioned, hold them in place with strips of tracing paper or thin glass strips like microscope slides, which prevent the wings from curling as they dry. Leave the specimen on the board in a warm, dry place for about 24 hours before removing it.
Wet Preservation for Soft-Bodied Specimens
Caterpillars, grubs, maggots, spiders, and extremely small insects don’t hold their shape when dried. These specimens need to be stored in liquid, specifically 70% isopropyl alcohol or ethyl alcohol. Drop the specimen directly into a small glass vial filled with the solution.
For caterpillars and other larvae, there’s a trick that produces much better results: keep them alive until you get home, then submerge them in boiling water for one to two minutes before transferring them to alcohol. This kills bacteria in the digestive tract that would otherwise cause discoloration, keeping the specimen’s original colors more intact.
For specialized collections, certain groups benefit from modified solutions. Thrips and most mites preserve better in a mixture of eight parts ethanol, five parts water, one part glycerin, and one part glacial acetic acid. The glycerin helps keep very small specimens from shriveling.
Rehydrating Dried Specimens
If a specimen dries out before you can pin it, or if you find a dead insect you want to mount, you’ll need to soften it first in a relaxing chamber. This is easy to build at home. Place a few sheets of paper towel in an airtight plastic container and soak them thoroughly with a 50/50 mix of rubbing alcohol and water. Set a small dish on top of the wet towels and place your dried insects on the dish. Seal the container and wait 24 to 48 hours. The humid environment slowly rehydrates the joints and tissue so you can position the legs, antennae, and wings without breaking them. The alcohol in the mix discourages mold growth while the specimen softens.
Labeling Your Specimens
An unlabeled bug is scientifically worthless, but even for a personal collection, labels make the difference between a meaningful display and a box of anonymous insects. Every specimen needs at minimum three pieces of information: where it was collected (county and state), when it was collected, and who collected it.
For pinned specimens, write this information on a small paper label and push it onto the same pin below the insect. Write the date with the month in Roman numerals between the day and year (for example, 15-VII-2024 for July 15, 2024) to avoid confusion across date formats.
For wet specimens in vials, place the label inside the vial with the specimen. This is critical because labels on the outside of vials eventually fall off or become unreadable. Use soft-lead pencil or India ink on the label. Ballpoint pen and most printer inks will dissolve or run in alcohol.
Protecting Your Collection Long-Term
The biggest threat to a pinned insect collection isn’t time or dust. It’s dermestid beetles, tiny scavengers whose larvae will devour dried specimens from the inside out, leaving nothing but hollow shells. Older guides recommend naphthalene mothballs, but these are toxic and largely unnecessary if you take a few practical steps.
Store your collection in boxes with tight-fitting lids. Wooden display cases designed for insect collections (Cornell drawers or Schmitt boxes) work best, but even sturdy cardboard boxes stored inside sealed ziplock bags will keep pests out. Freeze any new specimens for a full week before adding them to your collection, which kills dermestid eggs or larvae that might be hitching a ride. Keep the lids on whenever you’re not actively working with the collection, and periodically inspect your specimens for signs of fine dust beneath them, which is the telltale calling card of dermestid damage.
For wet-preserved specimens, the main concern is evaporation. Check your vials every few months and top off the alcohol as needed. Use vials with tight-sealing caps, and store them upright in a cool location away from direct sunlight, which degrades both the alcohol and the specimen’s coloring over time.