The Sphinxes that aren't like the Others (Taxon of the Week: Smerinthini)

Female of the smerinthin moth Marumba quercus. Photo by Tony Pittaway.

Quick question - should the plural of "sphinx" be "sphinxes" or "sphinges"?

The sphinx moths or hawkmoths (Sphingidae) are one of the easiest lepidopteran families to recognise. Sphinxes tend to be fairly large (but not inordinately so), and are generally the speedsters of the moth world. Their rapid mobility is reflected in their wings, which are narrower, more streamlined and more pointed than those of other moth families. Sphinxes are not usually brightly-coloured, but they are none the less very handsome animals, with dapper patterns of earthy colours such as browns and soft pinks. The name "sphinx" is derived from their caterpillars - sphinx caterpillars have a way of sitting with the front of the body raised that is supposed to be reminiscent of the famed Egyptian statue.

Adult sphinxes are most famed as nectar feeders - with their long proboscides and ability to hover in front of the flowers they feed on, Old World sphinx moths have been described as the ecological counterparts of New World hummingbirds (I won't repeat the Xanthopan praedicta story here, but look it up if you're interested). One group of sphinxes, however, has decided to buck the trend. Sphinxes are divided into three subfamilies - Sphinginae, Macroglossinae and Smerinthinae. Smerinthinae are distinguished from the other two subfamilies because they lack the super-long proboscides. In at least one of the smerinthine tribes, Smerinthini, the adults are completely non-feeding (the subfamily as a whole is sometimes described as such, but the presence of pollen on proboscides of Ambulycini indicates that members of that tribe are still flower feeders - Beck et al., 2006). Adult Smerinthini are weaker fliers than other sphinx moths, and have less streamlined wings to match. Also, while caterpillars of other subfamilies tend to be fussy eaters, Smerinthini are relative gourmands, feeding on a wide range of host plants.


Paonias astylis, one of the few North American Smerinthini. The small-eyed and blinded sphinxes of the genus Paonias (so-called, I'm guessing, because the unusual relative position of the fore- and hindwings means that the eyespots on the latter are hidden) are perhaps some of the most distinctive sphinx moths. Photo by Jim McCormac.

Sphingidae as a whole are regarded as good dispersers, and European sphingid species tend to have wider ranges than moths of other families. However, a study of sphingid distributions in Indonesia found that, in line with their lower dispersal capabilities, smerinthine species showed a higher turnover between islands than members of the other two subfamilies (Beck et al., 2006). Smerinthini are mostly found in the Old World - only two species are found east of "Lydekker's line" between the Moluccas and New Guinea, and a handful of species are found in Nearctic North America.

It is easy to imagine a connection between the distinctive smerinthine life cycle and their poor dispersive abilities - with their short-lived adults and polyphagous larvae, female Smerinthini have neither the freedom nor the need to invest a lot of time in seeking out suitable host plants for their eggs. What is more uncertain is whether the smerinthine life cycle is derived from a more typically sphingid ancestor. The Smerinthinae have been suggested to be the basalmost subfamily of Sphingidae, and in some features they are more like members of closely-related families than other sphingids - their short proboscides (like Brahmaeidae) and preference for tannin-bearing trees over tannin-free shrubs (like Saturniidae). On the other hand, a genetic analysis by Regier et al. (2001) found support for a Sphinginae-Smerinthini clade excluding Macroglossinae. Mind you, Regier et al.'s analysis did not include representatives from the other smerinthine tribes.

Oh yes, and at least some Smerinthini have stridulatory apparatuses on their genital valves (Conner, 1999). These are singing moths.

REFERENCES

Beck, J., I. J. Kitching & K. E. Linsenmair. 2006. Wallace's line revisited: has vicariance or dispersal shaped the distribution of Malesian hawkmoths (Lepidoptera: Sphingidae)? Biological Journal of the Linnean Society 89 (3): 455-468.

Conner, W. E. 1999. 'Un chant d'appel amoureux': acoustic communication in moths. Journal of Experimental Biology 202: 1711-1723.

Regier, J. C., C. Mitter, T. P. Friedlander & R. S. Peigler. 2001. Re: Phylogenetic relationships in Sphingidae (Insecta: Lepidoptera): initial evidence from two nuclear genes. Molecular Phylogenetics and Evolution 20 (2): 311-316.