Typically we think of aphids as plant pests, existing solely on a diet of plant sap that they obtain by tapping into the phloem tubes of plants, using their specially adapted piercing mouthparts (stylets). These when viewed externally, when the aphid is feeding on the plant, look fairly straightforward as in this beautiful photograph of the Oleander aphid, Aphis nerii, from Lisa Sell’s great blog site Zen Through a Lens http://www.zenthroughalens.com/
The stylets can, however, actually take a rather convoluted route to their destination .
Adapted from Roger Blackman (1974).
This is, however, not the whole story. Some years ago when I was a PhD student, I was looking after a friend’s pea aphid (Acythrosiphon pisum) culture, whilst he was on holiday. One day, whilst adding new pea plants to the cages, I became aware of a sharp stinging sensation on my wrist. Looking down I was somewhat surprised to find that I was being probed by an aphid. After my initial shock I decided that the aphid had been confused by the pea plant scent on my hands and decided that I was a suitable host plant to investigate. The incident was not repeated although the story has become a feature of my lectures on aphid biology. Many years later, one of my PhD students who was working on the Asian ladybird, Harmonia axyridis, which she used to feed on pea aphids, came and asked me if I had ever heard of aphids eating each other as she had noticed that some of the juvenile pea aphids appeared to be feeding on some of the adults.
My response was in the negative, but I said I would do a bit of research on the subject for her. To my surprise, I found a short note (Banks et al., 1968), where the authors described not only incidents of aphids acting as cannibals and feeding on each other, but also of aphids acting as predators and feeding on the eggs of ladybirds and lacewings, a reverse of the normal situation. They also described an even more interesting report of what might have been biological control of a plant pest by another plant pest – in this case hop feeding mites were apparently being eaten by aphids, unfortunately not names so I was unable to follow it up. One of the authors also reported seeing many incidents of cannibalism by the aphid Megoura viciae, during some of his experiments. They also noted that there was a report of an aphid species that was capable of causing swellings and rashes on people in what is now Taiwan. I tracked the paper down (Takahashi, 1930) and had it translated by a PhD student and the paper was indeed entitled An Aphid that Bites People. Apparently the gall forming aphid, Ceratoglyphnia (Astegopteryx) styracicola, (pictured below alongside the gall)
is well-known to attack people who stand or sit underneath the snowbell tree, Styrax suberifolium, which incidentally has rather nice flowers.
The result of being ‘bitten’ by the aphid is a red swelling that disappears after an hour or so, but leaves a very itchy rash that can persist for two to three days. In fact this phenomenon is so common that people avoid passing underneath infested trees.
So those of you who thought that only your house plants were in danger from an aphid attack better watch out!
Aoki, S. & Kurosu, U. (2010) A review of the biology of Cerataphidini (Hemiptera, Aphididae, Hormaphidinae), focusing mainly on their life cycles, gall formation, and soldiers. Psyche, http://www.hindawi.com/journals/psyche/2010/380351/
Banks, C.J., MaCaulay, E.D.M. & Holman, J. (1968), Cannibalism and predation by aphids. Nature, 218, 491 http://www.nature.com/nature/journal/v218/n5140/abs/218491a0.html
Blackman. R. L. (1974) Aphids, Ginn & Co.
Takahashi, R. (1930) An aphid that bites people. Transactions of the Natural History Society of Formosa, 20, 43-44.
And new in 2015, here is an aphid that sucks the blood (haemolymph) from ant larva! Aren’t aphids wonderful?