The weather has turned cold, so now I have a little time to look at some of the images I have taken in the past.
I had a couple of occasions where I took photographs of aphids this last year. Aphids are very destructive crop and garden pests, so you would assume that they would be easy to find in the wild. In my experience, they are not. When you do find them you are likely to find a lot, but you might just as easily search unsuccessfully for them for a number of days.
Aphids have a number of interesting associations with other insects, and when I look for aphids I usually look for the other insects that go along with aphids.
Here is a classic ants tending aphids photo. Once I located this group, I went back to take more photographs, but the group was only there for two or three days, then they went somewhere else where I couldn’t find them.
Aphids seem to have a strategy of out-reproducing all of their enemies. They don’t try to run or fly off. They do attract ants for protection, but that has limits. They can give off toxic or nuisance chemicals to deter predators, but that too has limits. What they do is reproduce parthenogenetically (without mating), and give birth to live young. There are a couple of good descriptions of the life cycles at wikipedia and bugguide.
Here is an aphid with liquid at its cornicles. This individual is discolored so it may have an internal parasite. Near it are some shed exoskeletons, also discolored.
This photo from a heavily infested milkweed leaf shows the normally colored yellow aphids and some darker aphids, apparently parasitized.
Here the aphids seem to have an external parasite. They look like the larva of drynids, which are a type of wasp.
This seems to be something else–notice that the aphid is not discolored. I think this may be a syrphid maggot, but once again I am not sure.
I have read a lot about aphids and their associated predators, parasites, parasitoids, and benefactors. Trying to sort out what is actually there when you see them can be difficult, however. But that is part of the fun–if I already knew what was going on, there would not be much point in just trying to photograph it.