At first I thought this incredibly tiny creature was the early instar of a shield bug but, when I couldn’t find any pictures that resembled it on the British Bugs website, I turned to Twitter for help. Luckily, a botanist I know, Karen, had seen something similar posted recently in a Facebook group and very quickly supplied me with a name, Crypturaphis grassii, the Italian Alder aphid, so named because it’s only ever found on Italian Alder trees (Alnus cordata).
I found online a report published in 2011, on the first records of this species in Cornwall, which provides some interesting detail about these aphids. Apparently, Crypturaphis grassii is ‘native to southern Italy and Corsica and [was] first recorded in the UK in 1998’. Intrigued, I returned to the tree I’d found my first specimen on and found many more of these creatures, with variations in colour and markings. The report explains that:
Viviparous individuals [those able to birth live young] are yellowish-green to yellowish-brown, with brown spots extending along the dorsal surface, around the edge of the abdomen and on the head. Compound eyes are reddish in colour. … Immature apterae [wingless individuals] are similar but smaller, paler and lacking in dark spots, more translucent and slightly more elongate in shape. Oviparous apterae [wingless individuals that are able to lay eggs] are similar in size and shape to viviparous apterae but are brown in colour, with transverse darker abdominal stripes, rather than spots.
The Italian Alder, on which the aphid feeds, was ‘commonly planted as a roadside, waterside and/or windbreak species’ during the 1980s, and, by 2011 when the report was published, the aphids had already spread widely throughout Britain, including having established colonies in the Vale of Glamorgan, which is where I found the aphids in my photographs.
Citation: Luker, Sally. (2011). CRYPTURAPHIS GRASSII (STERNORRYNCHA: APHIDIDAE): FIRST RECORDS FOR CORNWALL. British Journal of Entomology and Natural History. 24. 205.