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The Nygmiini are most clearly defined by the well developed corethrogyne
in the female abdomen. The seventh segment is expanded and membranous, sometimes
with the basal margin stiffened as a sclerotised ring. This expanded membranous
zone bears a dense tuft of scales: these scales are used by the female to
protect the egg mass. Though this habit occurs in other lymantriid groups, it is
not accompanied by expansion of the seventh segment.
The forewing lacks an areole except in Rhypotoses Collenette
where its formation uniquely involves R1. The forewing facies is distinctive,
often colourful, involving dense scaling and, in the majority of genera, rather
bold, blocked patterning rather than fine fasciation. Where the latter occurs,
it is often paler than the ground, rather than darker. Some genera, such as Rhypotoses,
Cozola Walker and Medama Matsumura, have rather plesiomorphic
patterning with finer, darker, more crenulate fasciation. The discal spot, when
present, is a solid, dark dot rather than a V-mark or more typical noctuoid
reniform stigma.
Male genitalia structure is diverse and provides diagnostic features for
the various genus-groups recognised here, particularly within the very broad
concept of Euproctis Hübner that has previously been applied within the
Old World fauna (e.g. by Holloway (1976), Schintlmeister (1994) and Nielsen,
Edwards & Rangsi (1996)). A number of species groups have been recognised
and genus- group names applied mostly from within the old synonymy of Euproctis
(e.g. as in Nielsen et al.). Genus-group names based on African
type-species do not appear to be relevant to the Indo-Australian fauna, so it is
likely that different generic concepts will apply in that continent (Maes,
1984b). Maes referred a number of Madagascan species to his Sphrageidus Maes,
a genus based on the Palaearctic species similis Fuessly (See
Sphrageidus Maes). It has not been possible to place the genera Epeuproctis Matsumura
(type species tamahonis Matsumura) and Meteuproctis Matsumura
(type species tomponis Matsumura) within this new scheme. Both were based
on unique females with unmarked yellow forewings from Taiwan. It has been
possible to examine photographs of these and their genitalia. A preliminary
survey of Taiwan material of this facies type in BMNH did not yield a match.
The female genitalia are very variable in development, this tending to
reflect characteristics of the aedeagus vesica in the male. The signum is often
of the bicornute type, but this can be modified into a transverse flange or, in Nygmia
Hübner, a longitudinal one.
The larvae do not appear to offer any strongly definitive
characteristics, having secondary setae on verrucae as in other groups. The
postspiracular abdominal verrucae are reduced, and the subspiracular and
supraventral ones are well separated as in Orgyiini (Gardner, 1938). The
secondary setae on the verrucae can be highly urticaceous in some genera and,
when the larvae are abundant and gregarious, can be a health hazard (See Toxoproctis
Gen.n and, for the Palaearctic type species of Euproctis, de Worms (1979) and
Carter (1984)). In some genera (e.g. Sphrageidus, Arna Walker), Somena
Walker, Orvasca Walker and Artaxa Walker the dorsal pairs of
verrucae are particularly prominent on the first two abdominal segments and A8,
where they have converged and coalesced. Some Nygmia also have the
verrucae convergent and prominent on these segments.
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