Bagworm Moth

I photographed this Bagworm Moth when I was testing Panasonic Lumix DMC-FZ200 camera. Bagworms are a small family of moths approximately 1,300 species that make up the family Psychidae, in which all species’ larvae are enclosed in a bag and most species have flightless adult females. One can find a variety of ‘bags’ built by these little creatures. Some are really amazing feats of engineering, while some others look clumsy. These bags they carry, camouflage beautifully with their environment. Bagworms can feed on many different plants and are considered an occasional pests.

Adult bagworms will often go unnoticed in the landscape, especially the female, because she is enclosed in her bag and inside of her pupal casing throughout her life. In many species of bagworms, the adult female’s wings and appendages are greatly reduced to vestigial mouthparts and legs, small eyes, and no antennae or wings. The female remains in a caterpillar-like state, mates, and then becomes essentially an egg-filled sac. The male bagworm emerges as a freely flying moth. Neither the male nor the female adult feeds. The female lives a couple of weeks, while the male lives only one to two days.

Shortly after mating, the female lays a large egg clutch (500-1,000 eggs) inside of her pupal case enclosed within her bag. The eggs are smooth and cylindrical in shape and laid in a mass that is covered in a waxy, tuft-like layer. Hatching larvae are small (approximately 2 mm long) and often disperse to surrounding plants by spinning a silken thread and ‘ballooning’ on the wind. Once a suitable host is found, the caterpillar begins feeding and incorporating material into its bag, which it constructs with pieces of twigs, leaves, and silk. Only the head and the thorax emerge from the anterior end of the bag, so that the caterpillar can feed and move along plant material. If the bag were to be dissected, the posterior end of the caterpillar would appear medium to dark brown in color with the dorsal portion of the first three segments being white to yellow with a dark brown pattern. The common bagworm caterpillar develops through seven instars before it transforms into a pupae. The fully grown larva is approximately 25 mm long and takes up to four months to develop.

The mature larva attaches its bag to a branch with a strong band of silk. The pupa remains inside the bag and is dark brown to black in color. The pupal stage generally lasts for 7-10 days. Throughout the larval instars, the caterpillar increases the size of its bag as it grows and can survive long periods without food, especially during the later stages of development. Once the larva has consumed enough food during the last instar, it attaches its bag securely with a thick silken strand to its host plant or disperses to another structure. Prior to molting and pupation, the bagworm will seal the anterior portion of the bag.

Adult males emerge while females release a pheromone that attracts the male moths. During mating, the male climbs onto the female’s bag, hangs upside down, and extends and inserts his abdomen about 4 cm into the bag. Once mated, the female ceases production of pheromone and is no longer attractive to males. After oviposition, the female may die inside the bag, mummifying around her eggs, or may fall to the ground just before death. Since bagworm cases are composed of silk and the materials from their habitat, they are naturally camouflaged from predators. Predators include birds and other insects. Birds often eat the egg-laden bodies of female bagworms after they have died. Since the eggs are very hard-shelled, they can pass through the bird’s digestive system unharmed, promoting the spread of the species over wide areas.

In case you want to know more about these amazing creatures please go to my good friend Karthik’s Journal – http://www.wildwanderer.com/blog/?p=1985.