Insects as Bioindicators of Water Quality
Bioindicators are biological systems that can show (indicate) a measurable effect. Aquatic insects can be bioindicators of water quality.
The Indiana 4-H bioindicator cards show larval stages of aquatic insects that may be found in Indiana streams. The cards use a tolerance score (0-10) to estimate water quality. The score represents the insect’s sensitivity to pollution. Insects with a score of 0 are intolerant to pollution (cannot tolerate any water pollution). Insect families with a score of 10 are very tolerant of polluted water.
Materials Needed: data sheet, dip net, plastic bowl or dishpan (white), egg cartons or ice cube trays (2-3, white), and a stream to sample. Using white pans and trays makes it easier to see the insects.
- Bioindicators of Water Quality: Quick Reference Guide (Purdue Extension publication ACE-11, 2016) — the PDF version is free to download. You can order printed copies for $5.50 each (plus shipping).
- Bioindicators of Water Quality Flash Cards (mobile version) (Purdue Extension publication 4-H-1018-M, 2012) — these flash cards are designed for use on mobile devices and show aquatic insects.
- Locate a stream to sample. The stream should only be knee deep (at most). You should have easy access to the water. Make sure you have permission to sample the stream.
- Take samples from all stream habitats along a 200-foot section. Jab your dip net against the vegetation and into mud or sand in the riverbed to collect insects. Scrape the underside of rocks and logs into the net.
- Put stream water in the dishpan and ice cube tray so insects don't dry out. Collect insects for 45 minutes. You should place captured insects in the dishpan.
- Sort the insects that look the same into different compartments of the ice cube tray using your hand or forceps.
- Use the bioindicator cards to identify the insects. Record the number of insects from each insect family you identify on the data sheet. Place the insects back in the stream when you are finished.
- Complete the calculations and determine the stream water quality rating.
The cards are grouped by insect order and identified to the family level. Insects with a tolerance score of “undetermined” are not included on the data sheet.
These instructions are in a Word document
Assessing the Water Quality for Your Site
- Determine the Family Tolerance Score by multiplying the number of insects in each family by the tolerance value given for that family.
- Determine the Order Totals by summing the number of insects and Family Tolerance Scores for each Order.
- Determine the Grand Total by summing the Order Totals (number of insects and Tolerance)
- Determine the Biotic Index by dividing the Grand Total tolerance score by the Grand Total number of insects.
- Estimate the stream water quality rating and degree of organic pollution from the Biotic Index table.
Biotic Index Table