Artemesia aphids

Absinthe Aphids (Macrosiphoniella absinthii) on Shrubby Wormwood (Artemesia arborescens)

When I looked out the office window the other afternoon, I noticed a dark smudge at the top of one of the Artemesia plants in the herb garden. Intrigued, I ventured out for a closer look and found these colourful aphids (photographed by Mike). A sniff around the internet led me to the amazing Aphids ID website run by the folks at Influential Points. This site packs a serious punch. It has detailed ID information for hundreds of species, with some great pictures as well. Sifting through the plant list (you can search for potential aphids IDs by checking the plants on which they're feeding) quickly led us to our list's latest addition — the Absinthe Aphid (Macrosiphoniella absinthii). Its one of only 25 species of aphid that Carl Linneaus himself named, in the 10th edition of his seminal work, Systema Naturae. As is suggested by its name, it's typically found on Absinthe plants. We don't have Absinthe in the garden, but we do have a close relative — Tree Wormwood (Artemesia arborescens). And that's where these little creatures have made themselves at home. They feed only on the upper parts of various Artemesia species. All of the insects you see in the picture are female. Like other aphids, this one typically reproduces parthenogenically. For most of the year, females give birth to only to other females, which are clones of their mother. And those newly-born females are already pregnant with clones of their own. In the autumn, some males will also be produced, and these will then reproduce sexually with some of the females. This allows for a bit of gene mixing (provided, of course, that they're not just mating with their sisters).

These little aphids are unexpectedly colourful; many aphids solidly green or brown or grey. The bold pattern may help to make the aphids less obvious to passing predators by helping to break up their outline. Alternatively, it may aposematic, indicating to potential bird predators that the aphids are toxic; the compound thujone in Artemesia plants render the aphids inedible to birds. The two little spikes sticking up from the aphids' back ends are called siphunculi (or cornicles); they're tubes that exude a defensive fluid if the aphid is threatened. The pointy "tail" is known as a cauda; the aphid uses it to flick away its excrement (also known as honeydew because of its high sugar content). Unlike some aphid species, this one is not guarded by ants. This species naturally occurs from northern and central Europe, north Africa and the Mediterranean region east to Siberia and Iran, and has been accidentally introduced to the US, Canada, and Argentina. Our record appears to be the first for East Anglia — how exciting! Of course, it could also just mean that most people aren't looking...