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 cecushing@aol.com
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
Email: streamdoctor@aol.com
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 streamdoctor@aol.com.
Originally published May 17th, 2004 on Fly Anglers Online by Robert Younghanz.