Dickson’s Opal, Chrysoritis dicksoni (Gabriel, 1947) was discovered in September 1946 by Charles Dickson near Melkboschstrand. It has always been a scarce butterfly, and has had a history of disappearing from its known habitats and then being rediscovered. Its original known strongholds were in the area between Melkboschstrand and Mamre on the Cape West coast. These colonies were lost one by one through expansion of agricultural activities and encroachment of alien vegetation. The last area where it occurred on the west coast was near the Pella mission station, where it had eight sub populations over an area of 60 ha. These colonies also died out and by the mid-1990s it was effectively extinct on the west coast. A population that had been found near Witsand on the south Cape coast in 1979 also disappeared. However, persistent searches by Ernest Pringle led to the discovery of more localities further inland. The butterfly is holding on at these sites, but is severely threatened by alien plant invasions at one site.
IUCN RED-LIST STATUS
Originally Red-Listed as VULNERABLE (Henning & Henning 1989), it was upgraded to CRITICALLY ENDANGERED in the latest revision of the Red List, following the loss of the west coast populations (Henning et al. 2009), and this status was confirmed in the South African Butterfly Atlas (Mecenero et al. 2013).
CURRENT SCIENTIFIC KNOWLEDGE
Melkboschstrand, Western Cape.
There are two main, disjunct population groups. One group was found on the West Coast between Melkbosstrand and Atlantis (three colonies, now all apparently ‘extinct’). The other population group occurs near Witsand (at the mouth of the Breede River). The West Coast populations fluctuated in numbers significantly from year to year before their eventual extinction (Heath & Brinkman 1995). The Witsand populations have remained strong since their discovery by the Pringles, and recent research has shown that they are spread over an area of some 10 hectares (Curle & Ficq 2009; Edge & Terblanche 2010).
Clark & Dickson (1971) described the habitats north of Cape Town as a sandveld type, with short vegetation. Near Atlantis, the species was found in Atlantis Sand Fynbos (Mucina & Rutherford 2006), with the dominant plants being peperbos, Montinia caryophyllacea Thunb. (Montiniaceae), and dakriet (Restionaceae) amongst which the associated ant builds its nests (Henning et al. 2009).
The habitat north of Witsand is in Canca Limestone Fynbos (Mucina & Rutherford 2006), with the dominant plants being Passerina vulgaris, an unknown Poaceae species, Thamnocortus pluristachyus Mast., and Searsia glauca (Thunb.) Moffett. The latter two plant species are utilised by the host ants Crematogaster peringueyi to build their carton nests. The butterfly and the ant species appear to be particularly sensitive to habitat alteration, and colonies move their exact location every few years
Adults fly from around mid-August towards the latter part of September.
Male territorial behaviour
Adult males are decidedly gregarious and congregate at certain spots in open sandy areas (similar to ‘lek’ behaviour in moths) (Clark & Dickson 1971, Curle & Ficq 2009). When disturbed they fly low in circles, often settling again on low vegetation or on the ground, returning sometimes to the same perch.
Mating takes place when a female enters the ‘lek’ area and after a contest between the males present the victor mates with the female. Mating has also been observed taking place straight after emergence when a male and female hatch close after each other, on top of the ants’ carton nest. Coupling lasts for about twenty minutes and the ants do not attack the pair.
Female oviposition behaviour
Females fly randomly about the habitat, and are sometimes encountered far away from known breeding sites. They oviposit on many different plants and substrates (Edge & Terblanche 2010), and this is strong evidence of their aphytophagy.
Clark & Dickson (1971) described the egg and first instar larva, which died fairly soon after hatching. Alan Heath and his co-workers conducted much field research as well as captive rearing experiments with this species (Heath & Brinkman 1995; Heath 1998; Heath & Claassens 2000, 2003; Heath et al. 2008; Heath 2014). The larvae were found to be aphytophagous (do not feed on plants at all), and to be associated with ants (Crematogaster peringueyi)and Homopterans (aphid-like insects). The larvae are fed by ant regurgitations (trophallaxis). Heath & Brinkman (1995) described aspects of the population dynamics of Chrysoritis dicksoni based on their collections and observations in the field. They hypothesised that individuals could remain in the larval or pupal state for more than one year, if conditions were not favourable.
Originally allocated to genus Phasis Hübner, 1819, but after investigation of its morphology and life history it was transferred to the monotypic genus Oxychaeta by Tite & Dickson (1973). Heath (1997), in a revision of the tribe Aphnaeini, synonymised Oxychaeta with Chrysoritis Butler, 1898 on morphological grounds, a treatment that was later supported by DNA analysis (Rand et al. 2000).
Threats to existing populations
Alien vegetation; overgrazing; small population effects. With increasing alien vegetation, fires became more frequent, and this could be a threat to the ants’ carton nests which are above ground and quite flammable.
Correct vegetation composition and structure is essential to promote the right conditions (microclimate) for the host ants and the scale insects which suck sap from certain plant species. Fire is not important in this arid climate.
Research on the butterfly’s life history and ecological requirements is continuing and includes study of:
- Adult butterfly behaviour and habitat requirements
- Female butterfly oviposition (egg laying) behaviour
- Observations of the larval stages of the butterfly, including its association with ants and Homopterans.
- The vegetation occurring in the habitat of the butterfly, both in terms of species composition, but also structure and age.
- The preferred microclimate conditions necessary for the butterfly and its early stages and associates.
- Sampling and identification of ant species assemblages and Homopteran populations at the places where the butterfly occurs.
- The population of the butterfly at its various locations.
- The impact of various management techniques (burning; cutting of vegetation to create open areas) on the butterfly’s presence and breeding success.
The remaining known populations occur on two privately owned farms north of Witsand, spread over an area of c. 20 ha. One of the farms is well managed, with good control of alien vegetation and moderate levels of grazing, and as long as this regime prevails the butterfly should be safe. The other farm is poorly managed by a tenant farmer who has no incentive to manage the area for the butterfly’s benefit. The land has been historically overgrazed and it is heavily infested with alien vegetation (mainly Rooikrans Acacia cyclops). Nonetheless the butterfly has survived in several places, although the population seems to be in decline. CapeNature is active in the area and has offered to enter into a stewardship agreement with the landowner (Stellenbosch University).
Clark G.C. & Dickson, C.G.C. 1971. Life histories of the South African lycaenid butterflies. Cape Town: Purnell.
Curle, A.I. & Ficq, H.C. 2009. The plot thickens – Chrysoritis dicksoni (Gabriel, 1947): some recent field observations. Metamorphosis 20(4): 108–114.
Edge, D.A. 2005. Butterfly conservation in the southern Cape. Metamorphosis, 16(2): 28–46.
Edge, D.A. 2016. Vegetation associated with the critically endangered butterfly Chrysoritis dicksoni (Gabriel, 1947) (Lepidoptera: Lycaenidae: Aphnaeinae) at Witsand, Western Cape Province. Metamorphosis 27: 66–77.
Edge, D.A. & Giliomee, J. 2015. The ants and scale insects on which the critically endangered butterfly Chrysoritis dicksoni (Gabriel) (Lepidoptera: Lycaenidae: Aphnaeinae) depends for its survival. Metamorphosis 26: 38–43.
Edge, D.A. & Terblanche, R.F. 2010. Research into the life history and ecology of Chrysoritis dicksoni (Gabriel) (Lepidoptera: Lycaenidae). Metamorphosis 21(3): 120–127.
Gabriel, A.G. 1946. A new species of Phasis (Lepid. Lycaenidae) from South Africa. The Entomologist 80: 60–61.
Heath, A. 1997. A review of African genera of the tribe Aphnaeini (Lepidoptera: Lycaenidae). Metamorphosis Occasional Supplement 2: 60 pp.
Heath, A. 1998. Further aspects on the life history of the myrmecophilous species Chrysoritis dicksoni (Gabriel) (Lepidoptera: Lycaenidae). Metamorphosis 9(4): 160–172.
Heath, A. 2014. Uncovering secrets of the ‘cuckoo’ butterfly species Chrysoritis dicksoni (Gabriel, 1947), a social parasite of Crematogaster ants: A summary to the end of the 20th century with current conclusions. Metamorphosis 25: 5–10.
Heath, A. & Brinkman, A.J. 1995. Aspects of the life history, distribution and population fluctuations of Oxychaeta dicksoni (Gabriel) (Lepidoptera: Lycaenidae). Metamorphosis 6(3): 117–127.
Heath, A. & Claassens, A.J.M. 2000. New observations of ant associations and life history adaptations (Lepidoptera: Lycaenidae) in South Africa. Metamorphosis 11(1): 3– 19.
Heath, A. & Claassens, A.J.M. 2003. Ant-association among southern African Lycaenidae. Journal of the Lepidopterists’ Society 57: 1–16.
Heath, A., McLeod, L., Kaliszewska, Z.A., Fisher, C.W.S. & Cornwall, M. 2008. Field notes including a summary of trophic and ant-associations for the butterfly genera Chrysoritis Butler, Aloeides Hübner and Thestor Hübner (Lepidoptera: Lycaenidae) from South Africa. Metamorphosis 19(3): 127–148.
Henning, G.A., Ball, J.B. & Terblanche, R.F. 2009. South African Red Data Book: butterflies. SANBI Biodiversity Series 13. South African National Biodiversity Institute, Pretoria.
Henning, S.F. & Henning, G.A. 1989. South African red data book: butterflies. South African National Scientific Programmes Report 158. Pretoria: Council for Scientific and Industrial Research.
Mecenero, S., Ball, J.B., Edge D.A., Hamer, M.L., Henning, G.A., Krüger, M., Pringle, E.L., Terblanche, R.F., Williams, M.C. (2013) Conservation assessment of butterflies of South Africa, Lesotho and Swaziland: Red List and Atlas. Saftronics (Pty.) Ltd., Johannesburg & Animal Demography Unit, Cape Town.
Rand, D.B., Heath, A., Suderman, T. & Pierce, N.E. 2000. Phylogeny and life history evolution of the genus Chrysoritis within the Aphnaeini (Lepidoptera: Lycaenidae), inferred from mitochondrial Cytochrome oxidase I sequences. Molecular Phylogenetics and evolution 17: 85–96.
Tite, G.E. & Dickson, C.G.C. 1973. The genus Aloeides and allied genera (Lepidoptera: Lycaenidae). Bulletin of the British Museum of Natural History (Entomology) 29: 225–280.