Twin-spot Plume Stenoptilia bipunctidactyla
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.
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.
- Larva (Description: Ian F. Smith):
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.
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.
Foodplant: Flower of Knautia arvensis. Late July.
Second instar (in Knautia flower )
Head: Pitchy black.
Prothoracic shield: Pitchy black.
Thoracic legs: Black.
Body: Maroon. Venter paler shade of maroon.
Anal plate: Blackish.
Early larva (in Knautia flower )
Length: 3 mm
Head: Black. Mouthparts reddish brown.
Prothorax (T1): Large black spiracle. Prothoracic shield pitchy brown.
Thoracic legs: Black. Tarsus blackish brown. Claw brown.
Body: Dull red, covered in dense shiny spicules. Below the level of the spiracles, the spicules are grey-black and give a slightly sooty appearance. The subdorsal line, lateral line, subspiracular line and venter are dull translucent yellow.
Spiracles: Pitchy brown.
Pinacula: Dull yellowish.
Setae: Primary setae whitish. Black secondary setae beginning to appear, not fully developed.
Anal plate: Pitchy brown.
Prolegs: Transparent, almost colourless, slight greyish tint.
Intermediate larva (in Knautia flower )
Length: 6 mm
Head: Whitish yellow, marbled with brown in posterior of epicranium and on adfrontal area. Black posterolateral mark. Black mark either side of epicranial sulcus at posterior. Stemmatal area black. Mouth parts light reddish brown.
Prothorax (T1): Yellowish white. Large spiracle with pitchy black peritreme. Prothoracic shield yellowish white, paler than head. divided by light medial line which is margined by black dashes and dots. Black lateral dot.
Thoracic legs: Black. Tarsus translucent yellowish brown. Claw brown.
Body: Reddish maroon. Heavily shagreened by spicules. Venter yellowish. Whitish subdorsal line. Whitish pinacula arranged to form discontinuous lateral and subspiracular lines. Spiracles: Pitchy black peritreme.
Setae: Primary setae whitish translucent. Many secondary setae; larger ones yellowish white, smaller ones black.
Anal plate: Yellowish brown. Translucent. No anal comb observed.
Prolegs: Translucent yellowish white. Thinly tubular. Crochets pitchy brown.
Late instar larva (in Knautia flower )
Head: Whitish semitransparent. Two longitudinal bands of dark reddish brown marks in posterior half of epicranium. Adfrontal area stained brown. Black posterolateral mark. Pitchy black marks either side of epicranial suture. Stemmatal area black. Mouthparts brown.
Prothorax (T1): Green. Large spiracle with black peritreme. Prothoracic shield greenish white, divided by a green medial line, which is edged by black dashes and dots. Black lateral dot.
Thoracic legs: Black. Tarsus translucent yellowish brown. Claw reddish brown.
Body: Apple green, heavily shagreened by spicules. Dark red dorsal line bordered by greenish white subdorsal line. Broken white lateral and subspiracular lines containing white pinacula.
Spiracles: Pitchy brown.
Pinacula: Small whitish, located in whitish lines.
Setae: Stout opaque white primary setae. Secondary setae shorter and black, except white when located on white lines. Anal segment: Greenish. No anal comb. Anal plate brownish white translucent with some black dots. Red dorsal, and white subdorsal, lines of body extend onto anterior of plate.
Prolegs: Very thin, tubular. Greenish white. Crochets black. Anal prolegs stouter than others, and have yellowish white planta.