The best way to preserve a dead bug depends on what kind of bug it is. Hard-bodied insects like beetles, butterflies, and grasshoppers are best preserved dry, typically pinned and mounted. Soft-bodied insects like caterpillars, aphids, and larvae need to be stored in alcohol to keep their shape. Getting this choice right at the start makes the difference between a specimen that lasts decades and one that crumbles or shrivels within weeks.
Dry Pinning vs. Liquid Preservation
The first decision is whether your bug should stay dry or go into liquid. As a general rule: if the insect has a hard exoskeleton and rigid wings, pin it. If it’s squishy, translucent, or larval, preserve it in alcohol.
Good candidates for dry pinning include beetles, butterflies, moths, dragonflies, grasshoppers, cicadas, wasps, and most adult flies. These insects hold their shape well when dried and can be displayed on pins for years.
Insects that should go into alcohol include caterpillars, grubs, maggots, aphids, termites, silverfish, fleas, mealybugs, and basically any larval stage. These soft-bodied specimens shrivel badly when dried and become extremely fragile. Flies (Diptera) are also risky to store dry because their heads, legs, and antennae detach easily.
One important exception: adult moths, butterflies, mosquitoes, and anything with scales or fine hairs on the wings should never be placed in alcohol. The liquid destroys their scales and matts their hairs, making them worthless as specimens. Adult bees have the same problem since their dense body hairs clump together in liquid.
How to Pin Insects
You’ll need entomological pins, which are longer and thinner than regular sewing pins. They come in sizes from 000 (thinnest) to 8 (thickest), and size 2, at about 0.46 mm in diameter, works for most insects. Sizes 1 and 3 are the next most useful. All standard entomological pins are 38 mm (1.5 inches) long. You can find them from entomological supply companies online for a few dollars per hundred.
Push the pin through the middle of the thorax (the middle body section, between the head and abdomen), positioned just slightly to the right of the center line. For butterflies and moths, you’ll also want a spreading board to flatten the wings into a display position. Gently push the pin through the center of the thorax, then use strips of paper or wax paper pinned over the wings to hold them flat while the specimen dries.
For very small insects that are too tiny to pin directly, you can glue them to a small triangular point of card stock, then push the pin through the card. This technique works well for anything smaller than a housefly.
Drying Time
After pinning, the specimen needs to dry completely before handling or storage. Allow at least five days at room temperature for most insects, longer for large or thick-bodied ones. If you have access to a drying oven set to about 40°C (104°F), you can cut that to roughly two days. The insect should feel completely rigid before you consider it done.
How to Preserve Bugs in Alcohol
The standard preserving liquid is 70% ethanol (ethyl alcohol mixed with water). This concentration works well for most soft-bodied insects and larvae. You can purchase ethanol from scientific supply companies, or use high-proof grain alcohol diluted to approximately 70%. Isopropyl alcohol (rubbing alcohol) at 70% also works for casual collections, though ethanol is preferred for long-term or scientific use.
One problem with dropping soft-bodied insects straight into 70% alcohol is that they can still shrivel somewhat. For better results, first “fix” the specimen by placing it in boiling water for about one minute (for large caterpillars, grubs, or maggots), then transferring it to alcohol. This fixes the proteins inside the body and prevents the specimen from turning black. A chemical fixative called Kahle’s solution also works: soak the specimen in it for about a week, then transfer to 70% ethanol for permanent storage.
There’s one concentration exception worth knowing. Parasitic wasps and similar delicate, membrane-winged insects preserve better in 95% alcohol, which prevents their thin wings from twisting and folding. But most soft-bodied insects become stiff and distorted at that concentration, so stick with 70% unless you know you need the stronger solution.
Store alcohol-preserved specimens in tightly sealed glass vials. Check them periodically, because alcohol evaporates over time, even through sealed lids. Top off the vial with fresh alcohol whenever the level drops.
What About Formaldehyde?
Older guides sometimes recommend formalin (a formaldehyde solution) for preserving insect specimens. This is not a good option for hobbyists. Formaldehyde is a potent irritant to the eyes, skin, and respiratory tract, a known sensitizer that can cause allergic reactions, and a probable human carcinogen. It can cause chemical burns to the throat and stomach if accidentally ingested, and as little as 30 mL of a 37% solution has been reported to cause death in adults. Ethanol is safer, widely available, and works just as well for insects. Skip the formaldehyde entirely.
How to Soften a Dried-Out Specimen
If you find a dead bug that’s already stiff and brittle, or if you stored one in an envelope and now want to pin it properly, you’ll need a relaxing chamber. This is simply a sealed jar that rehydrates the insect with humid air until its joints become flexible again.
To build one, place one to two inches of clean sand in the bottom of a large airtight jar (a mason jar works). Saturate the sand with water and add a few drops of carbolic acid (phenol, available at some pharmacies) to prevent mold. Set your dried specimens in a small open dish on top of the sand, seal the jar tightly, and wait. Most specimens become flexible enough to pin within 24 to 48 hours, though larger or very dried-out bugs may take longer. Check daily. Once the legs and wings move without snapping, the insect is ready to pin.
This technique works well for butterflies, dragonflies, and large beetles. A traditional method called “papering,” where specimens are stored flat in folded paper envelopes or triangles, has been used for decades to transport butterflies and moths before they’re formally pinned. The relaxing chamber brings these papered specimens back to a workable state.
Labeling Your Specimens
A preserved bug without a label loses most of its value, even for a personal collection. At minimum, each specimen should have a small label noting where it was collected (as specific as possible, ideally down to county and state), the date of collection, and your name or initials. 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 pinned specimens, mount the label on the same pin, below the insect. For alcohol-preserved specimens, use a small slip of paper written in pencil (ink dissolves in alcohol) placed inside the vial.
Protecting Your Collection Long-Term
The biggest threat to a dry insect collection isn’t time. It’s other bugs. Dermestid beetles, also known as carpet beetles, are the most common destroyers of preserved insect specimens. Their larvae eat dried insect bodies from the inside out, leaving behind tiny shed skins (called exuviae) and a pile of dust where your specimen used to be. Spider beetles, booklice, and even cockroaches can also cause damage.
The best defense is airtight storage. Keep pinned specimens in sealed display cases, shadow boxes with tight-fitting glass fronts, or specialized entomological drawers called Cornell or Schmitt boxes. Any new specimens you add to a collection should be monitored for a week or two before placing them near your existing bugs.
If you spot tiny shed skins or fine dust around a specimen, freeze the affected insects for at least a week. Major collections use freezers set to around minus 30°F, but even a standard home freezer will kill most pests if you leave the specimens in long enough. Older methods relied on chemical fumigants like mothballs (naphthalene or paradichlorobenzene), but most institutions have moved away from these due to health concerns. Keeping your storage containers sealed and your collection area clean is more effective and far safer.
For both dry and liquid collections, store specimens in a place with stable temperature and humidity. Fluctuations encourage mold, corrosion of pins, and degradation of preserved tissue. A climate-controlled room, or even just an interior closet away from exterior walls, is better than a garage or attic.