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Mayfly - Callibaetis - male

Mayfly - Callibaetis - Male
Burlington, Middlesex County, Massachusetts, USA
September 4, 2008
Size: 8 mm (approx)
On a glass door at 5:00 AM, an hour before sunrise.

The two tails are not much longer than the body.

This is a male Callibaetis subimago. Nice shot, John.

=adult on bugguide?
Thanks. Does a subimago get marked as adult, immature, or neither on bugguide?

Good question
The short answer is that the mayfly subimago is a subadult or preadult form. The long answer becomes a tricky word game and depends on what is meant by the terms "adult" and "mature" as they pertain to mayflies.

Most mayflies undergo a unique second molt from subimago to imago in the fully-winged stage. However, in some mayfly lineages the second molt to the imago (adult) has been lost in the females, and they mate, oviposit, and die as subimagoes. The genus Ephoron ( here ) is probably the most commonly encountered example of this among North American mayflies. Some have argued that the final stage should be called the imago in these instances, but these females have basically the same structure as the female subimagoes of other mayflies.

The question of maturity further complicates the issue. In terms of sexual maturity, it is assumed that male mayflies need the final molt in order to develop effective sexual apparatus (fully-formed genitalia and grasping apendages). However, there is evidence that female mayflies are capable of being fertilized in the subimago stage. This obviously applies to those lines in which the second molt has been lost, but may also apply to many other (most?) female mayflies. In addition, a few mayfly species may be either partially or completely parthenogenetic (capable of reproducing without fertilization), and a few those exhibit oviposition through abdominal bursting in the subimago.

So, mayfly subimagoes fall between the cracks of the "adult/immature/neither" categories. On the slim chance that I haven't already told you more than you really wanted to know, you might want to read the paper "The Mayfly Subimago" by Edmunds and McCafferty (Ann. Rev. Entomol. 1988. 33:509-29). It is available online.

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