Zygaenidae

The taxonomic history of this family has been reviewed in detail by Yen et al. (2005), who stated that the monophyly of the current concept of the family had never been tested cladistically up to the point of their study. Holloway et al. (2001) treated the family as containing subfamilies Phaudinae, Procridinae, Callizygaeninae, Zygaeninae and Chalcosiinae, but contemporaneous and subsequent publications have been weighted in favour of excluding the Phaudinae as a distinct family, Phaudidae.

The analysis of Yen et al. (2005) did yield a major clade representing the Zygaenidae as a whole, but the suite of characters supporting it does not provide a clear and easily observed definition of the family; many of the supporting characteristics probably occur in taxa outside the analysis, possibly within the broader Zygaenoidea, and most are minutiae of structure such as the presence of curvature of the scales on the vertex of the head, or reduction of the second segment of the labial palp to shorter than the basal one. The molecular analysis of Niehuis et al. (2006) gave strong support for the monophyly of the family, excluding the Phaudidae.

The most useful character in the adult is that the chaetosemata include scales amid densely arranged sensilla. They tend to be large and may form a collar across the dorsal part of the head (particularly the Callizygaeninae and Chalcosiinae). The adults also release defensive cyanic fluids from below the compound eyes.

The uniquely definitive characters identified by Yen et al. (2005) are all in the larva: the presence of a cross-muscle around the mid-gut; the presence of cuticular cavities for storing cyanic fluids (but see Niehuis et al. (2006); the larval defensive secretion includes sarmentosin. The major components of these defensive fluids that were thought to be characteristic of the family (Naumann et al. 1999), lotaustralin and linamarin, were found not to be definitive of this major clade. Linamarin is present in the Heterogynidae but absent from some Procridinae, and lotaustralin is also absent from a few Procridinae. The larvae are usually highly aposematic and may have warty protuberances or secondary setae on verrucae.

The two-walled cocoon is spindle-shaped or a modification thereof, and has densely packed crystallites in the outer wall. Such crystallites are not seen in Phaudidae. In common with other Zygaenoidea, the pupa is protruded at eclosion.

The adults are mostly aposematic, day-flying and may be involved in mimicry rings, particularly the Chalcosiinae, where distinction from members of these rings in other lepidopteran families may be facilitated readily by examination of the venation: the medial vein stem is often present within the cell, certainly on the hindwing; the distal veins in the radial and medial sectors may have a somewhat sinuous appearance, tending to curve in towards branching points. The types of mimicry rings are discussed by Yen et al. (2005) and involve butterflies (Pieridae, Danainae, Papilionidae), Noctuidae (Agaristinae), Geometridae (Milionia Walker, Dysphania Hübner), and Erebidae (Arctiinae (Syntomini, Nyctemera Hübner, and the Damias Boisduval group of genera of the Lithosiini) and Aganainae). Some of these rings were surveyed more broadly by Holloway et al. (2001: 24-25).

The subfamily Zygaeninae is not represented in Borneo, showing its major diversity in the Palaearctic and Africa. It has been shown clearly to be monophyletic (Naumann et al., 1999). The Procridinae are discussed below; the full analysis of Yen et al. (2005) placed them as paraphyletic to the rest of the family, though analyses on male characters only, and on a somewhat smaller set of taxa where immature stage data were available, recovered the procridines as a clade. The Callizygaeninae were placed as sister-group to the Heteropanini and Chalcosiinae in the full analysis of Yen et al. (2005). The monophyly of this triplet was strongly supported: apparent reversal, relative to outgroups, of reduction of the proboscis to basal lobes; reduction of the maxillary palp; extension of the area of chaetosemata over the head, as mentioned earlier; several parallel modifications of the female genitalia; development, in the larva, of a thoracic shield and presence of a tonofibrillary platelet on the SD (subdorsal) verruca; seven features of larval chaetotaxy; increase in the spinules of the pupal abdominal tergites (two rows in Callizygaeninae, but also Phauda; multiple rows in Chalcosiinae); hardening and flattening, with dorsoventral compression, of the cocoon.

However, in the subsidiary analyses of the smaller set of taxa where immature stage data were available, Callizygaena ada Butler was placed as a solitary outlier in an unresolved trichotomy with a Chalcosiinae clade and a clade that recovered the Procridinae with, variously, Zygaeninae and the exemplars of Himantopteridae, Phaudidae, Lacturidae and Heterogynidae.

The molecular analysis of Niehuis et al. (2006) recovered exemplars of the four subfamilies as monophyletic clades, placing the Zygaeninae in a sister-relationship to a clade including the other three, with Callizygaena placed as sister to a clade consisting of the four chalcosiine exemplars, this clade being sister-group to the Procridinae clade.