08 June 2013

Life History of the Grass Demon

Life History of the Grass Demon (Udaspes folus)

Butterfly Biodata:
Genus: Udaspes Moore, 1881
Species: folus Cramer, 1775
Wingspan of Adult Butterfly: 37-45mm
Caterpillar Local Host Plants: Cheilocostus speciosus (Costaceae, common name: Cane Reed, Spiral Flag, White Costus), Costus lucanusianus (Costaceae, common name: African Spiral Flag), Hedychium coronarium  (Zingiberaceae, common name: White Ginger Lily, Butterfly Ginger), Zingiber officinale (Zingiberaceae, common name: Ginger), Curcuma longa (Zingiberaceae, common name: Tumeric).

Physical Description of Adult Butterfly:
Above, the wings are dark brown. The forewing has large white hyaline spots in spaces 1b, 2 and the distal end of the cell. Smaller white spots are found conjoined in spaces 3 and 4, singly in space 5, and conjoined in spaces 6 to 9. The hindwing has a large white discal patch with irregular outline. Underneath, the wings are reddish brown. In the hindwing, the tornal area is paler brown with the large white discal patch extended to wing base. A large irregularly shaped dark brown spot occurs in spaces 1b and 2. The antenna has a whitish band just below the club.

Field Observations of Butterfly Behaviour:
Grass Demon is moderately common in Singapore. The adults are typically found in parks, park connectors and gardens where one of its many host plants in the Zingiberaceae and Costaceae families are cultivated. The adults are fast fliers among the ground cover and shrubbery. They have been observed to visit flowers for nectar, and perch on sun-bathing spots with open wings.

Early Stages:
The early stages of Grass Demon are polyphagous with its host plants mainly belonging to the Zingiberaceae and Costaceae families. The caterpillars feed on the leaves of the host plants, and live in leaf shelters constructed by cutting and folding and securing leaf fragments with silk threads.

Leaf shelters for 1st and 2nd instar caterpillars.

Local host plant #1: Cheilocostus speciosus (White Costus).

Local host plant #2: Hedychium coronarium (White Ginger Lily).

The eggs of the Grass Demon are laid singly on the upper surface of a leaf of the host plant. The hemispherical egg is wine-red mottled with milky white patches. It has a base diameter of about 1.4mm.

Two views of an egg of the Grass Demon.

Two views of a mature egg, with the caterpillar's head visible through the hole in the shell in the right view.

The egg takes about 3-4 days to hatch. The newly hatched has a length of about 2.5mm and has a black head capsule and a yellowish orange body. A few relatively long setae adorns the posterior end. A black collar mark is present in the prothoracic segment.

The dorsal view of a newly hatched caterpillar of the Grass Demon eating its egg shell, length: 2.5mm.

After hatching, the young caterpillar eats the empty egg shell for its first meal, and then moves on to construct its first leaf shelter, typically at the leaf tip. From the shelter, it then ventures out to eat the nearby leaf lamina for subsequent meals. The body takes on a green undertone as a result. The growth in this first instar is moderately paced and the body length reaches about 6.2mm in about 2-3 days before the moult to the 2nd instar.

Two views of a 1st instar caterpillar, late in this stage, length 6.2mm.

A late 1st instar caterpillar, dormant before its moult.

The 2nd instar caterpillar is yellowish green in body colour. The head capsule is still black, but the black collar mark on the prothorax is now absent. At the posterior end, the relatively longer setae are longer present, and the anal plate is now marked in greyish brown. This instar lasts about 2-3 days with the body length reaching 9.5-10.5mm.

Two views of a 2nd instar caterpillar, early in this stage, length 7.4mm.

Two views of a 2nd instar caterpillar, late in this stage, length 9mm.

A late 2nd instar caterpillar, dormant prior to its moult.

The 3rd instar caterpillar resembles the 2nd instar caterpillar closely. The anal plate is darker and almost entirely black. A whitish patch encircles each of the two spiracles on the 8th abdominal segment. This instar takes about 3 days to complete with body length reaching about 19-29mm.

Two views of a 3rd instar caterpillar, early in this stage, length 9mm.

Two views of a 3rd instar caterpillar, length 15mm.

A late 3rd instar caterpillar, dormant prior to its moult.

A Leaf shelter for 3rd and 4th instar caterpillars.

The only obvious change seen in the 4th instar caterpillar is in the anal plate which has become entirely black and much more prominent than in the earlier instars. This instar takes about 4 days to complete with body length reaching about 29-30mm.

Two views of a 4th instar caterpillar, early in this stage, length 20mm.

Two views of a 4th instar caterpillar, late in this stage, length 29mm.

A late 4th instar caterpillar, dormant prior to its moult.

The 5th and final instar caterpillar loses the prominent black marking on the anal plate seen in the 4th instar. The anal plate is now in yellowish green, the body base colour. The 5th instar lasts for about 6 days, and the body length reaches up to 40-43mm.

Two views of a 5th instar caterpillar, early in this stage, length 30mm.

Two views of a 5th instar caterpillar, late in this stage, length 39mm.

A Leaf shelter for a 5th instar caterpillar.

Two views of a 5th instar caterpillar, late in this stage with colour change taken place, length: 40mm.

On the last day of the 5th instar, the body of the caterpillar shortens and changes to a milky shade of yellowish green. It ceases feeding and comes to a halt on the under surface of a leaf of the host plant. Here the caterpillar spins a short transverse silk band and a silk girdle. At the same time, a moderate amount of white waxy substance is secreted by the caterpillar and spread over the pupation site. With its posterior end secured to the silk band via claspers and the body secured at the mid-section with the girdle, the caterpillar enters its immobile pre-pupatory stage.

A pre-pupatory larva of the Grass Demon.

Pupation takes place about 1 day later. The yellowish green pupa secures itself with the same silk girdle as in the pre-pupal stage, but with the cremaster replacing claspers in attaching the posterior end to the transverse silk band. The long and slender pupa has a long rostrum and is unmarked. Length of pupae: 37-38mm..

Two views of a pupa of the Grass Demon.

Two views of a mature pupa of the Grass Demon.

After about 7 days of development, the pupa turns black as its skin turns translucent with the development within the pupal case coming to an end. The dark forewing upperside with its white markings are now discernible in the wing case. The following day, the adult butterfly emerges from the pupal case.

A newly eclosed Grass Demon clinging onto its empty pupal case.

  • [C&P4] The Butterflies of The Malay Peninsula, A.S. Corbet and H.M. Pendlebury, 4th Edition, Malayan Nature Society.
  • Butterflies of Thailand, Pisuth Ek-Amnuay, 2nd Edition, 2012
  • A Field Guide to the Butterflies of Singapore, Khew S.K., Ink On Paper Communications, 2010.

Text by Horace Tan, Photos by Benedict Tay, LC Goh, Loke PF, Anthony Wong and Horace Tan


  1. Amazing pictures!!..The Grass Demon was one of the first butterflies I clicked..loved reading its lifecycle here..:-)

  2. Thanks, Preethi. :)
    There are two more "Demon" skippers in the Singapore checklist. Their life histories will be posted too in due course.

    1. It's good to know that Horace - Will look forward to it!!:-)

  3. What a thorough post, and superb pictures.

  4. Wow, thanks a lot for this. I have been rearing a Caterpillar and wanted to get ID. Now I know it is grass demon.

  5. Horace can I use some of the picture in my life cycle video

  6. Thankyou for the information... Very insightful!... I have 2 pupas in my balcony... Since 4 weeks now .. and there is no development... They haven't yet turned into mature pupas... Any reason you know why?