Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Big dark ones are adult aphids.
Little green ones are juvenile aphids.
I do not recognize the different shaped one. It is mosquito shaped.
Aphids have an interesting life cycle:
While the living is easy the females reproduce by bearing live young.
When fall comes they lay eggs that will overwinter.
Sometimes they have wings and fly to new food sources. They seem able to get inside houses to infest house plants and the above water portions of aquatic plants. When they come indoors they leave behind their natural predators, so the population can explode really fast.
If the plant is moveable (in a pot, in this case) I would take it outside and spray it with insecticidal soap. Then hose it off to remove the pesticide before bringing it back in, just to be sure the insecticidal soap will not get into the aquarium or pond water.
If it is just a few aphids, then hand removal, perhaps with a bit of tissue. They do not move much, and are easy to wipe away.
If the plant is in an aquarium, and cannot be hurt by bending it over I dunk it in the tank and slosh it around. This removes a lot of the aphids and the fish eat them. This is not possible with the Arrowhead- it would break the stems.