Birth of a Backswimmer (Friday 5)

A few months ago, I posted a series of photos for Friday 5 that depicted the development of aquatic snail eggs.  In addition to the two species of snails I had in my tank at the time were a bunch of backswimmers in the genus Notonecta.  The morning after I put them in the tank, I came across a bunch of what could only be backswimmer eggs attached to a leaf, so I started photographing them.  I thought their development was fascinating and spent a little over two weeks watching the snail and the backswimmer eggs to see what happened.  Today I give you the Notonecta part of the story!

The eggs started out looking like what I would consider pretty standard true bug eggs:

Notonecta eggs, 1 day old

Notonecta eggs, 1 day old

They were simple to start off, just translucent white cylindrical eggs with rounded ends.  Many eggs were attached to this leaf in a sort of neat little line along the edges, but there were others attached to rocks and even a few stuck to the large rams horn snail that was oozing its way around the tank, so I suspect this was simply a convenient place to deposit them rather than a preferred method of placement.  In just under a week, some changes were evident:

Notonecta eggs, 6 days old

Notonecta eggs, 6 days old

This photo isn’t as well focused as I’d like, but it illustrates two things.   First, the structure of insect egg shells is absolutely stunning!  All of that patterning mirrors the cells that laid down the chorion (= the insect eggshell), so you’re effectively looking at structure of the mother’s internal organs when you look at an insect chorion.  In both eggs you can also see some faint red markings, more distinctly in the egg on the right.  Those red patches are the developing eyes of the backswimmers, so you can see which end is the head and which is the tail.  What was previously a little cylinder of bug goo had turned into the start of a baby insect with clear evidence of the changes visible without dissecting the egg in just a few days.

Things started to change more rapidly after the first eye spots were visible.  By day 10, the eggs looked like this:

Notonecta eggs, 10 days old

Notonecta eggs, 10 days old

The red eye patches had taken on the shape of backswimmer eyes by this point.  You could also see some black markings within the egg.  The bugs inside were clearly further along than they had been.  You could also easily spot the eggs that were not developing and were never going to hatch at this point.  The egg on the left side of the image was having problems and wasn’t developing properly – it has no eyes or any black patterning visible.  It never hatched.

Shortly before they hatched, you could see all sorts of structures inside the eggs:

Notonecta eggs, 18 days old

Notonecta eggs, 18 days old

You can’t see it very well without enlarging the photo (click to enlarge!), but you can see the outline of the plates on the upper surface of the thorax, the legs, and that the black markings are part of the legs.  By this point, the eggs were two and half weeks old and a few had hatched.  The empty chorions in the lower right corner highlight the cap of the egg the nymph inside popped open to emerge from the egg and a membrane that lined the chorion.  The eggs in this image hatched over three days (if they hatched at all), so they seemed to have some variability in their developmental times.

This is what came out of the egg:

Notonecta first instar

Notonecta first instar

The first instar nymphs were tiny, just a few millimeters long.  You can clearly see the bright red eyes and the black claws, both of which were visible through the egg chorion as they developed.  And, as a bonus this week, this is what these tiny nymphs eventually turn into:

Notonecta mature adult

Notonecta mature adult

The coloration becomes a lot more complex, they gain wings, and their bodies elongate relative to their width as they age.  Check out those gorgeous eyes on the adult!  And, these insects are fairly large, about 1 cm, which means that they have to grow a lot to become adults, and they do it very quickly.  That tiny nymph emerges from the egg and molts just 5 times before it becomes an adult, which means massive growth spurts each time they molt.

I know it probably makes me weird, but I love watching insect eggs develop!  They undergo some pretty amazing changes in a very short amount of time, plus they’re beautiful to look at and you can often see through the chorion and peek at what’s happening inside.  Eggs might not move, but they’re still fascinating and I am thrilled I got an opportunity to document how these eggs developed!  I hope at least some of you find it as interesting as I did.  :)

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Unless otherwise stated, all text, images, and video are copyright © C. L. Goforth
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