What do you call an immature dragonfly? Sounds like I’m setting up a joke, I know, but it’s a legitimate research question. Odonatologists are unique—as far as I know—amongst biologists who study non-holometabolan insects, in that they refer to instars as “larvae.” I never quite understood why, or at least considered it legit, until recently.
My main study taxon, Hymenoptera, exhibit a developmental trajectory called holometaboly, which means that the immature stages are radically different, both phenotypically and ecologically, from adults:
The top image shows what I think of as a larva. The wings aren’t obvious, the legs are tiny, the antennae are minuscule, the color is different from the adult, the cuticle is mostly softer than the adult, it feeds on plants (adults feed on pollen and other insects), etc. Bottom line – the immature version (top) is a much different insect from the adult version (bottom). The term “larva”, to me, was reserved for insect immatures that are really different biologically fromt he adults and require a resting stage (the pupa) to transition from one to the other. (Note: I’m not sure these two photos are of the same species.)
Odonate instars also differ substantially from their imagos. Instars live (mostly) in water, while adults dominate the skies. Instars, unlike adults, also have gills, relatively small eyes, flattened heads, and prehensile labia:
But the wings are developing externally, they’re both voracious predators, and there is no pupa between these two forms. I always just referred to odonate instars as “immatures” or “naiads” to avoid controversy. “Immature”, unfortunately, also refers to adult stages that are not quite yet sexually mature, a process that may in some species take many days to complete.
Anyway, the odonatologist community seems to have settled this debate awhile ago, and the term “larva” appears to have won out. Our own George Beatty even wrote an opinion piece, which I don’t think he ever published. I just loaded it into Scholarsphere:
Beatty, G. H. (1960s?) Terms applied to the immature stage of Odonata. (unpublished manuscript)
What do you think? Are the biological differences great enough to warrant the use “larva” for juvenile odonates? Is this terminological debate even important?
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