07 March 2012

Collecting Odonata Nymphs

Collecting and Preserving Vouchers of Odonata Nymphs

It's easy to see why adult Odonata are so popular, but it’s important to remember that the aerial adult stage is just a small fraction of the life cycle of an ode. Since the nymphs (or larvae, depending on which term you prefer) are found in water, they are less obvious, nor are they as easily identified as the adult stage. However, collecting nymphs is a good way to record what's living in the aquatic habitats.


Ethan Bright and Joel Wiechsel in a stream in Livingston Co., 1998.

The techniques used for sampling nymphs differ, depending on whether you are collecting in moving water (lotic), such as a streams and rivers, or still waters (lentic), such as lakes and ponds. Lotic habitats may range from tiny creeks to large rivers. You will for the most part only catch nymphs when sampling the streams, ponds, seeps, and lake bottoms. Try to minimize disruption to the site where you are collecting. It’s standard to stand upstream from your kick-seine or D-ring net and dislodge the substrate so that the insects float into the device you are using. With sampling along the edge of banks and ponds, it’s typical to swish the net about in short strokes and then examine the contents.

Unless you want to get wet, chest waders or hip boots are a good idea. One can get by with wearing an old pair of sneakers, but spending a couple of hours in water can get old. With waders you avoid leeches, stay comfortably dry, and at the end of the day, your feet will feel so much better. Some aquatic situations are potentially dangerous to a lone collector, so it is advisable to collect with a companion. Bogs and fens and deep-muck-bottomed lakes can be places where a person collecting alone might get stuck for hours. Floating bog-mats can be dangerous, too. Streams and rivers have their own potential dangers. If you can avoid collecting alone, please do so. Additionally, in or near metropolitan areas, you might come into contact with polluted waters that are potentially hazardous. Waters might be polluted with organic matter or with sharp debris. A good set of chest or hip waders provide a measure of safety. I do not advocate wearing sandals or going barefoot when doing aquatic sampling, as there are too many ways to acquire an injury from glass, metal, or sharp rocks. In addition, algae-covered rocks can be slippery. Avoid wading where you cannot see the bottom!

For aquatic collecting, you will need a net designed for aquatic sampling, such as a D-net or similarly strengthened net with a long handle and strong nylon mesh (500-250µm mesh is best). You can also use standard kick-seines in riffle areas. Standard round insect nets are not good for this purpose. Small aquatic dip nets may be improvised from aquarium nets, strainers, etc. Larger D-ring nets can be purchased from vendors such as BioQuip. A white plastic or enamel pan is essential for examining your scoops of debris and muck in the field, and for separating out the nymphs. Much of the technique is pretty standard benthic invertebrate sampling, which can be found in many reference sources, such as this pdf.

Specimens to be preserved may be dropped into 70% ethanol or isopropanol. Specimens to be kept alive should be separated by size to avoid cannibalism and predation. Your samples can be stored in plastic vials, screw-top glass jars, or polyethylene "whirl-pack" bags. Some researchers keep their nymphs in water, and then preserve them at the end of the day by first dropping them into boiling water (which kills them instantly), and then placing them into ethanol.

Make sure that data accompanies preserved specimens - use either pencil or "pigma pens"on rag paper or card stock to prevent fading or leaching of ink.
Of course, in addition to Odonata nymphs, you will find a lot of other macroinvertebrates in your nets. If there are watershed surveys in your area, you may want to check with those groups to see if they might be interested in the other insects that you find. Caddisflies (Trichoptera), Mayflies (Ephemeroptera), and Stoneflies (Plecoptera) are commonly found while sampling.

Things to note during stream surveys:
•Type of habitat - riffles, cobbles, woody debris, sloughs, vegetated substrates
•Approximate width and depth of stream where sampled. Size and depth of lake, if a lentic habitat.
•Type of substrate - sandy, rocky, mucky, etc.
•Temperature, if possible
•Color of water - clear, tea-stained, turbulent, etc.
•Type of shoreline - high banks, rocky, etc.

SUBMITTING AQUATIC SAMPLES TO THE MOS.

So long as they are inside rigid containers, you can send exuviae in the dry state.

However, for specimens in alcohol, there are certain regulations for shipping that must be followed. It may be easiest to hand carry the specimens and pass them along to the MOS in person. If you wish to mail specimens to the UMMZ, please go to the following website for information on mailing wet specimens.

I'll admit that sampling for nymphs isn't nearly as exciting as trying to net a flying adult, but in terms of real science, there is a lot that we don't know about the immature stages of many odes. You may find that catching nymphs and trying to rear them to adults is a fun and rewarding experience. With today's plethora of digital recording devices, you can make movies of nymphs feeding, record a time-lapse movie of emerging adults, and whatever other behaviors that interest you.

In terms of trying to identify them, the place to start is here. Although the Michigan Odonata Larvae pages haven't been updated in a few years, it's the best thing out there so far.

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