Macroinvertebrate Sorting and Counting

Note: These procedures are recommended for advanced volunteer monitoring groups using Level-3 SOPs. In most cases Level-1 and Level-2 collection are assessed streamside.

Fill jar nearly full with 95% ethanol so that the concentration of ethanol is at least 70%. If there is a small amount of water in the sample, it may not be necessary to fill the jar entirely to reach a 70% concentration. It is very important that sufficient ethanol be used to reach 70% concentration. In addition, enough alcohol should be added to at least immerse all of the material in the jar. Make sure that a label for the inside of the jar is written in pencil (ink will run); include stream name, code, and date. Place the label inside of the sample jar. Place the jar in a cooler or other container designated for the storage of macroinvertebrates. Try to keep from shaking the jars as much as possible. Never invert the jars. All samples are brought to the lab/home for in-house sorting and identification or shipped to a contractor for sorting and identification (this is a substantial cost).

Sorting Equipment
 
 

Sorting is done utilizing a modification of the standard sub-sampling method. Macroinvertebrates are identified to the family level and the functional feeding group and tolerance values are determined. WV Save Our Streams suggest using a 300-organism sub sample or a one-quarter sub-sample procedure with an additional scan for rare taxa in certain circumstances.

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.