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Identification & Distribution:

The apterae of Aphis jacobaeae are dark green and are not wax powdered. The thorax has rather extensive dark lateral sclerites, whilst the abdomen has small marginal sclerites on tergites 2-4, small sclerites just behind the siphunculi, dark bands across tergites 7-8, sometimes a small median sclerite on 6, and dark intersegmental muscle sclerites. The alate has a similar pattern but the marginal and post-siphuncular sclerites are larger. The marginal tubercles are prominent. The siphunculi have a conspicuous apical flange. The legs are dark except for the extreme bases of femora. This feature will usually distinguish Aphis jacobaeae from Aphis fabae which also occurs on ragwort, but has pale tibiae. The body length of apterae is 1.8-2.2 mm.


The ragwort aphid does not host alternate. Sexual forms occur in autumn. It feeds on ragwort (Senecio jacobaeae) living basally or higher on the stem or on the flowers. They are usually attended by ants which may build earth tents over the aphids. The species occurs in western and central Europe and into Russia.


Biology & Ecology:

We have found Aphis jacobaeae in a range of habitats including chalk downland (especially common), old pasture, shingle ridge grassland and mixed woodland. The picture below shows a dense colony of Aphis jacobaeae on ragwort growing on old shingle ridge grassland. Most of the aphids in this colony appear to be alatiform nymphs, destined to migrate to lands anew.

The dynamics of aphid populations are influenced both by plant quality and the actions of natural enemies. Müller et al. (2005)  sought to assess the relative importance of fertiliser addition to plants and exclusion of predators for growth of Aphis jacobaeae populations in the field. NPK fertilizer was applied weekly to ragwort plants at two sites. There was no effect of fertilization on aphid populations at either site. Exclusion experiments demonstrated that predators were the main determinant of aphid colony growth. Ants were left unmanipulated in both sites and their performance on the aphid colonies did not significantly differ between sites or between treatments.

Vrieling et al. (1991)  looked at the interactions between ragwort, the aphid Aphis jacobaeae, the ant Lasius niger and the cinnabar moth (Tyria jacobaeae) and ragwort. Ragwort is protected from herbivores by high levels of toxic alkaloids. The larva of the cinnabar moth is able to sequester the alkaloids, rendering it harmless to the larva. But the larva is then toxic to vertebrate predators - hence the aposematic colouration (see picture below). Large numbers of larvae may completely defoliate ragwort plants. Ants defend ragwort plants infested with aphids against larvae of the cinnabar moth so such plants escape regular defoliation by cinnabar moth larvae. However, only plants with a lower pyrrolizidine alkaloid get colonized by aphids and ants. Natural variation in cinnabar population levels and hence herbivore pressure leads to the maintenance of genetic variation in pyrrolizidine alkaloid concentration observed in natural populations of ragwort.

The aphid also sequesters pyrrolizidine alkaloids, but it does not invest in aposematic colouration. Aphis jacobaeae has dark green cryptic colouration and is also defended by attendant ants. The ants may also build an earthen shelter over the aphid colony as shown below. This may be partly for protection, but also probably serves to maintain high humidity levels.


Farmers and horse owners are especially antagonistic towards ragwort, despite the fact that cases of poisoning are rather rare. Ants (attending aphids) on the ragwort are probably highly beneficial for livestock owners because they make it even more unlikely that cattle and horses will eat ragwort (try eating a mouthful of angry ants). The absence of cinnabar larvae, due to aphid-tending ants, will also favour plants with rather lower alkaloid levels. Moreover ragwort control, by cutting and/or pulling up ragwort, exacerbates the problems as the broken stems produce new plants.

We have encountered one appalling approach to ragwort control on nature reserves, namely the use of herbicides and burning. This was in the fragile, but heavily-used, habitat of Barrow dunes in Somerset (see picture above).


We have made provisional identifications from high resolution photos of living specimens, along with host plant identity. In the great majority of cases, identifications have been confirmed by microscopic examination of preserved specimens. We have used the keys and species accounts of Blackman & Eastop (1994)  and Blackman & Eastop (2006)  supplemented with Blackman (1974) , Stroyan (1977) , Stroyan (1984) , Blackman & Eastop (1984) , Heie (1980-1995) , Dixon & Thieme (2007)  and Blackman (2010) . We fully acknowledge these authors as the source for the (summarized) taxonomic information we have presented. Any errors in identification or information are ours alone, and we would be very grateful for any corrections. For assistance on the terms used for aphid morphology we suggest the figure  provided by Blackman & Eastop (2006).

Useful weblinks 


  •  Blackman, R. L. & Eastop, V. (2006). Aphids on the World's Herbaceous Plants and Shrubs. Vols 1 & 2. J. Wiley & Sons, Chichester, UK. Full text 

  •  Müller CB et al. (2005) Relative importance of fertiliser addition to plants and exclusion of predators for aphid growth in the field. Oecologia 143, 419-427.Abstract 

  •  Stroyan, H.L.G. (1984). Aphids - Pterocommatinae and Aphidinae (Aphidini). Handbooks for the identification of British insects. 2 (6) Royal Entomological Society of London.

  •  Vrieling, K. et al. (1991). Tritrophic interactions between aphids (Aphis jacobaeae Schrank), ant species, Tyria jacobaeae L., and Senecio jacobaea L. lead to maintenance of genetic variation in pyrrolizidine alkaloid concentration. Oecologia 86 (2), 177-182.Abstract 


Identification requests

Alan Outen, 6 June 2014

Yesterday the Beds Invertebrate Group were at Stratton Moat, Biggleswade (a medieval ancient monument). This was heavily overgrown with nettles and goosegrass in particular but with a lot of Red Campion and old apple and plum trees. Sadly very few aphids and the apples were completely devoid of these and psyllids. A good list of species generally was assembled nonetheless. Prior to the meeting however on the road verge right beside where I had parked my car, I found another aphid species that I think is new for Beds.

On Ragwort (Senecio jacobaea) I am sure that this one must surely be Aphis jacobaeae. The apterae are dull greenish and the legs are wholly dark. Although not evident from the first three images these were very well ant attended. I hope that I have this one right!

Image(s) copyright Alan Outen,  all rights reserved.


Bob, InfluentialPoints:

  • Aphis jacobaeae - yes, They seem to occur wherever ragwort does. Stroyan (1984) reckons it's probably widely distributed in Britain, but has been little recorded. (only Kent, Hertford, Glamorgan, Suffolk & Norfolk in England).

Many thanks Bob. Glad I at least got those right.