I am just curious. I had quite a few which seemed to be the same that summer but not the summer after. Do they take that long to reproduce? Or was the summer of 2011 very wet summer maybe have something to do with not seeing them?

I have 3 man made ponds on my property. Did they maybe come from there or are they more of a stream type? There is a C1 stream across the street bordering the woods but many run-off streams here and in the surrounding areas.

Barb-

Mayflies of genus Cloeon, which are represented by a single species, C. dipterum in North America, are primarily found in small ponds.

They are capable of producing more than one generation during a 12 month period, which is referred to as their being multi-voltine, or as bi-voltine in the case of (2) generations per year. I suspect their emergence in NJ probably occurs twice per year, with one emergence around the month of May, and around emergence around the month of September. Offspring of the September emergence would overwinter as larvae (nymphs), and emerge in May. And, offspring of the May emergence would emerge in September, at least in years where the thermal regimen (water temperature as measured in degree-days) is sufficient to support a 2nd generation. If this is more information than you would have desired, please accept my apology.

Thanks for sharing your knowledge with me Roger. I do have another question which I don't know if you would know the answer to as to why I did not see any in 2011. In 2010 I had a very nasty algae bloom in the main pond from fallen leaves. I was removing the algae and leaves by hand but it wasn't helping so my husband bought some chemical to help break it down. We started it right after the thaw in 2011. It is supposed to be safe for life in the pond. It did not seem to hurt the green frogs or tadpoles, diving beetles and their larva, what I think are leaches, backswimmers and dragonfly and damselfly naiads. Is the chemical more dangerous than they say and perhaps killing other life that I can not see?

Barb-

If such a variety of other insect larvae were (seemingly) unaffected by the application of this chemical your husband purchased to break up the algae bloom, it seems unlikely to me that the chemical was responsible for killing the mayfly larvae, either. I would be more inclined to suspect the severe algae bloom itself, which you experienced in 2010, may have so depleted the dissolved oxygen level of your pond as to create a sufficiently hostile environment for the overwintering mayfly larvae, that either none emerged in 2011, or so few did that they simply went unobserved.

However, please understand that this is the purest of speculation on my part, and probably not much more reliable than the answer you might receive, were you were to ask the next person who happens to fall in behind you at the grocery store checkout line.

I appreciate your opinion. I will have to pay better attention this year when the pond finally thaws. Most people think I am silly including my husband but I worry about all of the life in the pond, my property and the environment. I try to keep my life as chemical free as possible. Thank you again for all of your help!

You are certainly welcome. Would appreciate hearing a update following your 2012 observations, as Cloeon dipterum observations are a rarely reported, and from only a handful of states.