1508 Stenoptilia bipunctidactyla
(Scopoli, 1763)
Wingspan 17-25 mm.This widespread and common moth may be an aggregate of species with very similar wings. Reported foodplants include Devil's-bit scabious (Succisa pratensis), Field scabious (Knautia arvensis) and Small scabious (Scabiosa columbaria).
Differences in the early and intermediate instar larvae from Knautia and Succisa, illustrated on this site, may be due to diet, instar, season or normal intraspecific variation. They have similar genitalia, and larvae found on one foodplant can be reared successfully on the others. Alternatively, they may represent two species of the aggregate. The larvae overwinter at a very small size, on both plants.
Devil's-bit scabious, (Succisa pratensis), feeders:
In March and April, the 3 mm reddish larva, with only sparse primary setae, mines the mid rib of a Succisa leaf. As it grows, it develops many secondary setae, and feeds in a folded leaf in May. Green coloration supplants the red, until the larva is green with a dark red dorsal line bordered by greenish yellow subdorsal lines.
A second generation lives in the flowers in July.
Field scabious, (Knautia arvensis), feeders:
The first generation lives, until May, hidden behind a leaf sheath, eating into the stem of Knautia arvensis, usually within 20 cm of the ground. Feeding damage causes part of the stem to turn black, and black frass can often be seen exuding from the leaf axil.
The second generation of larvae, in July, feeds in the flowers. Up to 3 mm larvae feed inside individual florets, which have frass and holes eaten in the side. Larger larvae live between florets. (See 'Show detail' for full descriptions of second generation larvae on Knautia.)
The pupa, from both Succisa and Knautia feeding larvae, is light green with a red dorsal line and reddish caudal tinting. It is attached to the foodplant or a nearby plant stem.
The moths fly from dusk into the night, in two overlapping generations, from late May to early October, and are frequent visitors to the light-trap.
Similar species:
Specimens found as larvae on Scabiosa columbaria in the Breck District and at Settle, Yorkshire, have been attributed to Stenoptilia annadyctyla which has similar wings, but distinct differences in the female genitalia (C. Hart pers. comm.).
The adult moth is sometimes confused with 1509 Stenoptilia pterodactyla. The forewings of S. bipunctidactyla are grey-brown, while those of S. pterodactyla are ochreous brown or reddish brown. The costal cilia are white on unworn specimens of S. pterodactyla, but dark on S. bipunctidactyla.
The help of Colin Hart with this text is gratefully acknowledged.
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