The Stream Doctor

May 17th, 2004

Email YOUR Questions directly to the Stream Doctor. This is your opportunity to get an experts professional opinion on anything stream related.

Q. Just curious as to the life cycle of the common scuds found in the upper midwest (Ohio, Penn). What is the length of time they live and how often and how many offspring can an adult produce? What are the prerequisites for suitable spawning grounds for these (gravel, algae, Elodea, etc). I also notice that a lot of streams I fish have large numbers of sowbugs but no scuds; what are the water quality differences needed for each species? Any input would be great!! I enjoy reading your column.

A. This may get lengthy, so I'll try to answer each of your questions briefly and then let you know how to get more information if you want it. I will be generalizing somewhat because there are many species of freshwater scuds. Probably the two most common genera are Gammarus and Hyalella.

Life span: Most species complete a life cycle in less than a year.

Offspring: Generally breed from February through October. Most females produce one brood per life cycle although Hyalella has been known to produce 15 broods in 152 days. Each brood contains 15 to 50 eggs; Hyalella averages 18 eggs per brood.

Spawning requirements are essentially no different from living requirements. They are essentially found in water with low or medium carbonate content (soft), but Gammarus lacustris is known to occur in hard water. Hyalella is sometimes found in alkaline and brackish water. Abundant dissolved oxygen is vital. Sowbugs are found in a wide variety of habitats, from shallow springs to deep lakes. They are sometimes indicative of organic pollution.

I have gleaned the above information from Pennak's Freshwater Invertebrates of the United States, 3rd ed. If you'd like more information, let me know your address and I could xerox the pages relative to the amphipods and isopods and send them to you. Contact me at

If you have a question, please feel free to contact me.
~ C. E. (Bert) Cushing, aka Streamdoctor
105 W. Cherokee Dr.
Estes Park, CO 80517
Phone: 970-577-1584

The 'Stream Doctor' is a retired professional stream ecologist and author, now living in the West and spending way too much time fly-fishing. You are invited to submit questions relating to anything stream related directly to him for use in this Q & A Feature at

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