Macroinvertebrate counting and sorting

Sorting macroinvertebrates from survey samples (a procedure often referred to as "bug picking") is an extremely important step in the biological research.  The quality of the work performed by the "picker" influences the quality of subsequent processes, such as identification and data analysis.  A competent "picker" must be able to recognize the morphological diversity of aquatic organisms, as well as the various methods these organisms may use to hide themselves from predators.  The outcome of the final study may be affected, even if only a few organisms are overlooked during the picking process.  The table below provides a list of materials and supplies needed for this work.
 
Recommended supplies for bug picking and identification
(1) Larval tray: contains sample during the sorting process; (2) Tray: a white enamel or plastic tray used to separate family groups.  The tray can be marked into equal size grids ranging in size from 1 x 1 to 3 x 3 inches.  The grids help to estimate the numbers.  A very inexpensive option is an ice-cube tray or a plastic craft organizer; (3) Forceps: fine tipped forceps are used to remove the organisms from the debris and to manipulating specimens during examinations to determine identification; (4) Magnifier: an optical aid to illuminate and magnify the sample during the picking process; and (5) Taxonomic keys such as, dichotomous keys, illustrated keys, and other guides that may provide some family-level descriptions.
 

Once the collections are placed into larval pans you will need to sort and identify.  At times this can be very difficult in the field so your group may want to consider using alternate procedures such as preservation and sub-sampling.  This is a very important part of the survey procedure and it requires a great deal of time and some expertise. Use the steps below as a guide.  This procedure can vary based upon the contents of your collection.  Use the steps below as a general guide to the sorting procedure, or click-here for additional information.

 

1. Add a couple of inches of water to your main sorting tray and the others you will be using. Spread the sample out over the bottom of a white tray. Spend a little time watching the macroinvertebrates. See how they move and look at the different shapes and colors (the colors change when they are preserved).

2. Pick through your sample in the sorting tray. Use a pipette, tweezers, spoon or brush to transfer your macroinvertebrates to the wells in the ice cube tray, craft organizer or smaller tray. Place animals belonging to the same group in the same portions of the tray.  In some cases it may be simpler to sort through one order at a time, especially if multiple kinds are probable.  For example, Ephemeroptera (Mayflies), Plecoptera (Stoneflies) and Trichoptera (Caddisflies) also called the EPT’s, can be very abundant in healthy streams and these orders as well as Diptera (True flies) are likely to have multiple families present.

3. For the first 10–20 minutes, transfer any animal that you see from the sorting tray into the other trays. For the last 10–20 minutes, look particularly for animals that are uncommon. Fast moving macroinvertebrates will be obvious but some will only start to move after 10 minutes or so. If after 20 minutes you find an invertebrate you haven’t seen before, sort for another 10 minutes until you find no new families.  Note: You should not spend more than 30-minutes sorting your macroinvertebrate collections.

4. Identify your collections: There are many key guides available to identify your macroinvertebrates. A 10x magnifying loupe, magni-cube or low power binocular microscope is useful for looking closely at the animals.
5. Estimate the abundance or count the number of each type of animal in the tray sections. As you look for families and count or estimate abundance keep track of your tallies on the survey data sheet.  Use a pencil so you can erase or scratch though your numbers when different families are encountered or your abundance changes. If you find a macroinvertebrate you cannot identify, record this on your result sheet, giving a brief description of what you found. When you have finished, return the animals to the water, as close as possible to the collection site.
 

 
Note: If you plan to preserve your collections you must apply for and receive a scientific collection permit from the WV Division of Natural Resources.  

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