Although this observation and video don’t revolutionize science, they do provide some information that was missing about the life cycle of an insect, and, importantly, they allow the lucky finder to see something that presumably no other human had seen before.
In this case it’s a substantial part of the lifecycle of a “mantidfly“, Ditaxis biseriata. Mantidflies aren’t “true” flies, which are in the order Diptera, but fit within the order Neuroptera along with lacewings, antlions, and various relatives. Here’s the species at issue, and you can see from its forelegs why it’s called a “mantidfly”. It’s obviously a predator, and eats other insects:
Within the order Neuroptera, this species is in the superfamily Mantispoidea and the family Mantispidae. And in that family there are four subfamilies. The immature life stages of one of them, the Drepanicinae (of which D. biseriata is a member) wasn’t known or seen until now. The German Wikipedia entry (the only one) says this: “Die adulten Tiere leben räuberisch von anderen Insekten, über die Präimaginalstadien ist bisher nichts bekannt”, which I take translate as “the adult insects are predators on other insects, but the pre-imaginal stages aren’t yet known.”
But now they are. The discovery is reported a new paper in Biodiversity Data Journal by James B. Dorey and David J. Merritt (reference and free link below) and summarized in EurekAlert! The latter article says that Dorey is an entomology student at the University of Queensland, who saw a mass emergence of these creatures in his father’s macadamia nut orchard in northern New South Wales. Not knowing what they were, Dorey took a video and obtained some eggs from a female that produced larvae that could be identified. His mentor and lecturer, Merritt, helped identity them as D. bitaxa.
So the life cycle is this: the eggs are laid by mated females who live aboveground, which are presumably laid on trees and then hatch, with the larvae heading underground. What they do under there, how long they’re underground (remember, cicadas can live underground as preadults for 17 years), and what they eat, is still unknown: the relatives in the family eat spider eggs as larvae, but we don’t know about this family. The larvae probably molt several times, producing successively larger individuals (the stages are called “instars”), and then at some stage they form a pupa.
The remarkable thing about the pupa, unlike a butterfly cocoon or a Drosophila pupa, is that they’re mobile: the late pupa, which contains an adult insect that hasn’t yet hatched, is called a “pharate”, and in the case of D. biseriata it can move! This freaks me out, but here’s the video that shows a pupa who has already climbed a tree hatching (“eclosing”) into an adult. This is fricking amazing, at least to someone like me who studies insects that have immobile pupae. The pharate you see that hatches into an adult has walked about two meters up the tree, become static for a while, and then eclosedfrom its pupal case. This, taken in the wild, is a remarkable video as well as a first observation.
Be sure to watch this enlarged for full wonderment!
Here are some pictures from the paper. First, a pharate that’s walked up the tree and is ready to hatch:
So that’s what’s new, besides the fact that mass eclosion of the type seen by Dorey is also new: this phenomenon has never been reported in the family.
h/t: Matthew Cobb
Dorey JB, Merritt DJ (2017) First observations on the life cycle and mass eclosion events in a mantis fly (Family Mantispidae) in the subfamily Drepanicinae. Biodiversity Data Journal 5: e21206. https://doi.org/10.3897/BDJ.5.e21206