Q.
How long does it take for a mayfly to hatch?
A.
Boy, you sure know how to ask a question that
is almost impossible to answer. The reason
is fairly simple - there are hundreds of
different mayflies and each one requires a
certain thermal history to hatch. Further,
the thermal history may vary for the same
species in different geographical areas and
other environmental factors, such as food
supply, may also influence the developmental
time of the nymph. So, you see, there is no
definitive answer to your question because I
don’t know which mayfly you are talking about,
where it lives, or the thermal history of the
body of water.
Now that I’ve explained why I can’t give you a
good answer, I do want to tell you something
about how your question could be answered.
I’ve talked about this in previous columns,
but here it is again… As I said, each
species requires a certain thermal history
to mature from egg to adult. These are
usually measured in “degree-days,” and is
a summation of what temperatures the nymphs
have experienced and for how long. Thus, if
a nymph started growing for 10 days at an
average water temperature of 15oC, this would
be 150 degree days. If this were followed by
a 15 day period when the water warmed to 17oC,
this would be an additional 255 degree days and
a total of 305 degree days for this 25 day period.
Now if our hypothetical species required 4500
degree days to hatch, it would need 4195 more
degree days. If the water averaged 19oC the
rest of the season, it would take about 221 more
days, or a total of 246 days in this particular
temperature regime.
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 August 16th, 2004 on Fly Anglers Online by Robert Younghanz.