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Maintaining an Arthropod Collection

Christine Johnson helps maintain the collections in the Department of Entomology at the American Museum of Natural History. She inspects the specimen cases to be sure that none of the delicate parts of the brittle specimens have broken off, that all labels are in place, and that moisture and living insects have not damaged any of the preserved specimens. She also adds newly prepared and identified specimens to existing collections, making sure they are in the right place, according to order, family, genus, and species. It is a big job and one that requires meticulous care and extensive knowledge, but then the Museum's collection includes millions of arthropods, some more than 100 years old. 

We asked Chris what advice she had for students setting up and maintaining an arthropod collection on a smaller scale. The first thing she told us is that it is a big job, no matter how small the collection is. "Before going out to take specimens in the field, students should be aware of what's involved in keeping a collection: from killing, preserving, and identifying specimens to pinning and labeling them. And then it all has to be stored properly and checked periodically to ensure that everything stays in good condition. It can be a lot of fun, but it's also a lot of work," she said. 
Although entomologists use some dangerous chemicals to kill and preserve specimens, Chris had some good ideas for safe alternatives. "With just a few exceptions, most of what you catch can be put immediately into a jar filled with ordinary ethyl alcohol. This will both kill the specimens and keep them from becoming damaged until you are ready to dry and pin them for exhibit," she advised. 

Some specimens--butterflies, moths, and dragonflies--would be damaged by being put in alcohol even briefly. Dragonflies need special treatment to preserve their iridescence (see sidebar "Preserving Color," below). Chris recommends killing butterflies and moths by carefully placing them between two sheets of tissue paper or paper towel, then into a small box or plastic food container. Finally, put them in a freezer for a few hours. 

"You can kill any other specimens this way if you don't like the idea of putting them in alcohol," Chris said. But she cautioned that beetles may take longer to die. "You might even want to leave them in the freezer overnight," she said. You should also be careful about putting different kinds of living arthropods in the same container, she warned, since some types will eat other types, "and then you've lost your specimen." 

Some specimens are not suited to drying and pinning and should instead remain in alcohol. These include soft-bodied arthropods like spiders, termites, and caterpillars and other larvae. For these specimens, use forceps to carefully transfer each one to its own small vial. Fill the vial with alcohol and close it tightly. You can tape the label to the outside of the vial or, if it is small enough and written in pencil, put it into the vial along with the specimen. "Don't use ink," Chris warned, "because the alcohol will quickly blur what you have written." 

For specimens that will be pinned, the next step is drying, "except for specimens that are frozen, in which case you need to rehydrate them before you pin them." Chris noted that this is the only time dampness is not the collector's enemy. "Otherwise, they are more likely to break when you try to arrange the wings while pinning them." 

Chris told us that Peterson Field Guides: Insects, edited by Donald J. Borror and Richard E. White, gives detailed instructions for pinning most common types of arthropods. 

Chris recommends using forceps rather than your fingers whenever you handle specimens. "Most specimens are very small and quite fragile. Handling them gently with forceps will help prevent damage. If a leg or wing or antenna does break off, don't despair," she said. "Just cut a small piece of card stock, put a drop of white glue on it, pick up the piece with your forceps, and place it on the glue. Then you can put the card right on the pin, just under the specimen. That way, all parts of the specimen can be found in one place and you haven't lost an important piece of your collection." Chris told us that the same thing is done in museum collections. 

The next step is labeling. Chris told us there is a standard format for labeling that is used in museum collections worldwide:

  • scientific name of specimen
  • country, county, town or city; latitude and longitude where it was found
  • name of collector
  • habitat where it was found: for example, under a leaf, in a log, in the air
  • date when it was found

"A properly prepared and maintained arthropod specimen could last for hundreds of years," Chris told us. "I've seen specimens in the Museum's collections dating back to the late 1800s, and there are probably others older than that." It is unlikely your specimens will stay around that long, but it still makes sense to adopt some of the techniques Chris uses to protect the Museum specimens. 

Keep the collection dry. "Try to keep it out of a damp environment, such as a basement, but if moisture is a problem where you are, tape a packet of desiccant, available from scientific supply houses, to the inside of each specimen box." 

Be on watch for dermestidae. These little beetles--commonly called carpet beetles--can be found just about anywhere. "Even when a specimen box is closed, they get in, lay eggs, and then the larvae literally eat the specimens from the inside out," Chris warned. A telltale sign is a fine dust called frass, which looks almost like sawdust. Chris inspects the collections carefully and regularly--she suggests doing it once every three or four months. At the first sign of frass, she puts the entire specimen box in a freezer for two days. "If I see a dermestid beetle crawling in the specimen box, I'll take it out, but freezing will kill dermestidae larvae and prevent further damage to infested specimens," she explained. 
In the past, museum collections were protected from these beetles with mothballs and other fumigants, but Chris said that the American Museum of Natural History no longer uses these harmful chemicals. "We just keep a careful watch on things and freeze anything that looks suspicious," she said. 

Basic Equipment

  • fine forceps
  • hand lens
  • vials or small bottles with screw-on tops or rubber stoppers
  • alcohol (70-80%)
  • Styrofoam (cut to fit into specimen boxes)
  • insect pins (available from scientific supply houses) or tailors' straight pins (stainless steel and at least 2 inches long)
  • water-based white glue
  • card stock (for labels)
  • specimen boxes--these can be as fancy as glass-topped Cornell drawers, which come with individual unit trays, or Schmitt boxes, which have to be opened for display (both are available from scientific supply houses), or as humble as cardboard shoe boxes; with a piece of glass or Plexiglas fitted into the top, you will be able to see the specimens without opening the box.

Pinning Specimens

  • Specimens in Alcohol 
    Pour contents of vial onto a plate. Using forceps, carefully pick out individual specimens and place them on paper towel for 10 to 20 minutes. When they are almost dry but still soft, pin them. For flies and other insects with veined wings, gently arrange wings to show venation. 

    Remove specimens and pin them, gently arranging the wings. Leave the specimen box open for about an hour after pinning to allow everything to dry completely. 

  • Frozen Specimens 
    Put about an inch of water in a large plastic food storage container. Place a sheet of paper towel in the bottom of a smaller container and place frozen specimens on the towel. Put the smaller container into the larger one, taking care not to splash water onto the specimens. Leave the smaller container open, but close the larger one tightly and leave in a secure place (where it will not get bumped) for 24 hours. 

    Remove specimens and pin them, gently arranging the wings. Leave the specimen box open for about an hour after pinning to allow everything to dry completely.

Preserving Color 

Many arthropods have beautiful colors that are worth preserving if possible. The metallic sheen of a beetle, the rich velvety wings of a butterfly, the iridescent lacy wings of a dragonfly are among the fascinations of a well-prepared collection. Some of these colors will fade in bright light, so Chris Johnson advises keeping specimen cases with glass or Plexiglas tops in cabinets except when they are on display. "Being in daylight or incandescent light for several hours at a time won't hurt them, but I'd keep them out of direct sunlight if possible," she said. 
The wings of dragonflies tend to lose their iridescence soon after they are killed. Hazardous chemicals such as acetone are sometimes used to "fix" the colors before they fade, but Chris suggested a safe alternative. 
"When you're collecting in the field, fold back the wings and put the live dragonfly in an envelope so that you don't destroy the wings. Then tape the envelope shut and put it in a shoe box. You can put more than one dragonfly in the shoe box, as long as there's only one in each envelope. Later, freeze the specimin and rehydrate the dragonfly the next day. When it is soft enough to spread the wings, pin it."

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