First, allow me to say that I know exactly what aphids are
No mistakes here.
Last year I tried to set up a zero maintenance open top tank in my patio. At the time of setting up the tank, the plants included Sagittaria and Water Lettuce. The animals included Red Sherry Shrimps and Assassin Snails. There was no filter, only an air stone. No weekly water changes.
I planted a Rose in a pot next to my tank. I wasn't aware that it was infested with aphids. It took a very short time for the aphids to move to the tank and infest the Water Lettuces. Obviously, I could not use any chemical solution. My only solution was to remove them by hand, after a short time, I left them alone.
The shrimps, snails, and aphids bred like crazy. The Sagittaria growth was so much that the tank turned into a jungle. The water lettuces did not last the winter. The aphids moved to a new host: the Saggitaria. But that is an underwater plant so how does an aphid eat that? The leaves of Saggitaria are so long that they float on the surface of the water. The aphids walk on and eat the floating leaves. They also walk on the surface of the water and move to the other leaves.
Yesterday I gave a trimming to the Sagittaria leaves at the front of the tank. This allowed me to see the tank clearly. I have seen many crazy things in my tanks (including a very long, slender, crimson worm that looked a lot like a huge earthworm). Today, I saw the craziest thing that I have ever seen: an aphid(?) 40cm below the water, walking leisurely (it seemed to be very comfortable) on the Sagittaria leaves, and having the time of his life.
I have three hypotheses:
1. It was not an aphid, but another water insect (probably a very small water bug, exactly the shape and size of the aphids).
2. It was an unlucky aphid that was somehow forced 40cm below the surface of the water. Highly unlikely, because there was nothing to move it there. If it simply fell on water it would not sink but float to the surface.
3. It was a resilient aphid that moved by itself below the surface. I'm not sure if this is possible.
What is certain is that it is definitely an insect.
I could not investigate the creature under a microscope (it vanished in the Saggitaria jungle) but I took some photos and recorded its movements for a short time. In the video, it appears as if the creature is quite comfortable.
I am uploading some of the photos. The videos are huge, so I prefer not to upload them. But if you want to watch them let me know and I'll do my best (I'll have to circumvent internet filtering in order to upload the videos).
These are the aphids:
This is my Zero maintenance aquarium:
fb upload image
And this is AquaMan:
The are more photos. The original photos are 16MP and not cropped. The are two videos, both 1080p.