Collecting and Preserving Odonata (Dragonflies and Damselflies)
Always gather collection information and ensure that it is easily related to each specimen (see below). Record exact locality (including, if possible, lat/long or UTM coordinates), date, time, collector''s name, and any pertinent habitat and behavioral information -- data on the type of water body, dominant plants, reproductive behavior, etc. are extremely useful.
Collect live nymphs by sweeping aquatic habitats with a dip net. dragonfly nymphs are best kept in containers with a bit of wet moss or other vegetation to keep the humidity high. Once you are back home, drop them in water that has been brought to a boil, but removed from the heat source; leave them for 30 seconds, remove and place on paper toweling to remove excess water. Store in 70% ethanol. This heating coagulates the protein (preventing the disintegration of internal tissues) and preserves the color pattern much better than placement directly into alcohol does. Hot water can damage the caudal gills of damselflies, however. I put damselfly nymphs directly into 70% ethanol in the field, then replace it with fresh ethanol after returning home.
Exuviae (cast larval skins) should also be collected from aquatic plants, rocks, logs and other supports. I prefer to keep exuviae in 70% ethanol. You can also keep them dry and pin them through the base of the wing cases, placing a small drop of white glue at the point where the pin exits the base of the thorax ventrally.
Use a long-handled aerial net. A net opening of at least 18 and quot; makes the job easier (see BioQuip for purchasing a net). Some collectors feel that a dark net bag (black or green) is less conspicuous to dragonflies, and thus is more effective than a white one. White nets however, make it easier to find the specimen in the net and I generally prefer white because I have found it actually attracts certain groups, namely gomphids (club tails). A wide mesh (but small enough to hold the smallest specimens) is preferred because this reduces air resistance and allows a faster swing. A large mesh may not be satisfactory if you''re also collecting insects other than dragonflies and damselflies.
Observing patrolling dragonflies before swinging at them often pays off; positioning yourself in the most advantageous location, especially if it is somewhat concealed, is usually fruitful. When attempting to a dragonfly, move deliberately. Refrain from waving the net around; keep it as inconspicuous as possible. Swing at fast-flying agile species from behind as they fly by; many will easily dodge a net swung head-on.
When an adult specimen is captured, place it alive in a glassine envelope (available in several sizes -- I prefer 3.125 and quot; x 5. and quot; These can purchased at local hobby stores or BioQuip. Clip a very small portion of one or both of the bottom corners of the envelope; this will allow the acetone to fill and drain from the envelope easier (see below). The wings should be together above the abdomen. In general, put only one specimen in each envelope; they can damage each other. But place pairs caught in tandem or in copula in the same envelope if possible; face them away from each other. If they are too large to go together in a single envelope, make certain that you note they were mating or in tandem on both envelopes. You can write the locality or a collection number (cross-referenced to field notes) right on the envelope in soft pencil, india ink or other ink that is insoluble in acetone (see the acetone treatment describe below).
Teneral (recently emerged) adults are fragile and preserve poorly. Place them in paper bags for a day or two so that the cuticle hardens and the color pattern develops. If collected while emerging, the adult should be placed in a bag and the associated exuviae should be kept and cross- referenced to the adult specimen.
PREPARATION AND PRESERVATION OF ADULTS
While in the field keep the envelopes containing live dragonflies as cool as possible and always out of the sun. Store them in a non-crushable box. Tupperware boxes of the proper size are excellent for this purpose. For convenience, specimens are usually kept alive in the envelopes until the collector returns to base. This also allows time for the specimens to empty their digestive tracts; color is usually preserved better in a specimen with an empty gut. The color pattern of some species, especially some blue ones (e.g. Aeshna''s, Argia''s and amp; Enallagma''s) fades soon after capture. This fading can often be reversed by exposing the specimen to sunlight. However, if possible, such specimens should be treated in acetone immediately.
Acetone dehydrates the specimen and dissolves fat, reducing the decomposition of color pigments. Acetone is flammable, so use caution. Avoid breathing the fumes and absorbing the liquid through your skin. Acetone can be purchased at most hardware or paint stores. Keep the acetone in a wide-mouth plastic or glass jar or other container inert to the solvent. The wider the mouth, the better, but make sure that the lid is leak-proof. Pack the jar(s) in a box for stability if you take it in an automobile.
The dragonfly must be killed and its body arranged in the proper configuration before treating it in acetone, otherwise it may dry with its abdomen curled and wings and legs askew. I prefer to do this by dropping the specimen in the acetone outside of the envelope. As soon as the insect is dead, I remove the specimen and position it in the envelope. The abdomen should be straightened (to make measuring it easier) and the legs should be brought forward (so that they do not obscure the base of the abdomen). The envelope containing the dragonfly then is immersed, on edge, in the acetone. Sometimes you may want to kill dragonflies, especially larger species, by injecting acetone into the thorax and base of abdomen with a hypodermic needle. This introduces the acetone into the muscles and organs faster than simple soaking, and it seems to improve color retention in the larger specimens.
Leave the dragonflies and damselflies in the acetone for about 8-24 hours depending on size. I unusually process my specimens at night removing them from the acetone the next morning. You may also find it easier to take the envelopes out for drying when the next day''s catch is ready to go into the jar(s). The acetone should be replaced after a few batches have been processed, i.e. when it becomes pale yellow (indicating considerable dissolved fat). Drain the acetone out of the envelopes back into the jar (this is where snipping a little bit off the bottom corners of the envelopes will facilitate drainage). Dry the specimens while still in the envelopes in a well-ventilated place as quickly as possible. This is the critical step. To get the best specimens, they need to be dried as quickly as possible. When possible, I use a dryer such as a convection oven. If I''m in the field, I simply place the envelopes directly in the sun. The faster the drying occurs, the better the color preservation. A desiccant can be used in an enclosed container to help with the drying. I find it best to leave the specimens in the acetone for a longer period, rather than remove them when I have no way of drying them quickly.
When the envelopes are dry, store them in Tupperware or cardboard boxes that will withstand crushing. Store the envelopes vertically, like a card file, and DO NOT pack them tightly. At this stage specimens can be broken and flattened if jammed too closely together. Tupperware containers are good because their tight seal prevents most pests from attacking your specimens. In humid climates, the inclusion of silica gel desiccating packets helps keep the specimens dry.
If using acetone is impossible, simply dry the specimens as rapidly as possible after they have been killed. Placing the boxes containing specimen envelopes at close range over or under electric lights is helpful for drying. You can also put them on the dashboard of your car in the sun. The faster the drying occurs, the better the color preservation. In the tropics, acetone is invaluable, since air-drying specimens is difficult and specimen damage is common. Acetoned dragonflies may even resist damage by pests (ants, carpet beetles, psocids, mice) more than untreated ones.
Once the specimens arrive at a museum or other collection, they are taken out of the glassine envelopes and stored permanently in clear envelopes made of cellophane, mylar or polypropylene. These can be purchased from the International Odonata Research Institute. The identification and collection data are typed on 3 and quot; x 5 and quot; cards, which are inserted in the envelopes behind the specimen. The envelopes are then stored like a card file in drawers and cabinets. Here is an example of a properly preserved and curated dragonfly.