I’ve learned that wooden fences attract small animals, particularly on warm days. Today, a row of interesting cocoons was seen hanging beneath an uppermost rail. So I snapped a shot for identification.
But discovering the maker of this cocoon wasn’t that easy. Internet sources seemed to agree that it belonged to a bagworm-moth larva; but which one? Most sites suggested Thyridopteryx ephemeraeformis. However, a University of Florida article about T. ephemeraeformis suggested that this insect is rarely found in Florida.
I continued my search and discovered that this cocoon was made by Oiketicus abbotii, Abbot’s Bagworm Moth. Although the two moths have similar habits, the Evergreen Bagworm covers its protective sack with leaf fragments, while Abbot’s Bagworm uses sticks, usually arranged horizontally.
The life cycle of the bagworm moth is fascinating. In the spring or early summer, a hatchling emerges from the cocoon in the company of 500 to 1,000 nestmates. Each hatchling, only 2 mm long (1/25 of an inch), immediately releases itself to the wind on a silken thread, which carries it to a neighboring plant.
The youngster then immediately begins feeding and constructing a new pupal case, which becomes larger and larger as the youngster grows. The caterpillar gradually encases most of its body with debris, until only the head and thorax extend beyond its confines.
Although Abbot’s Bagworm secures its casing to its body with silk thread, some bagworms carry their constructions with their feet.
It takes two to four months for the larva to attain full size. It then attaches the protective casing to a tree (or fence), seals the opening, and repositions itself so that it’s head is facing downward. It then pupates inside of its constructed casing for approximately four weeks.
We usually expect a butterfly or moth to emerge from a cocoon, and sometimes it does – if it’s a male. Females, however, remain wormlike throughout their lives. They never develop wings, eyes, legs, or mouths. No mouth is needed, since adults never feed and adult lifespans are brief. In fact, females live only two weeks; the free-flying males a day or two.
The encased female emits a pheromone that attracts winged males. When a male finds a receptive female, he inserts his abdomen into an opening at the bottom of her home, through which the female maintains cleanliness. The female then lays her eggs, after which she dies within her sack or falls to the ground. The eggs are left to overwinter indoors.
Bagworm moth larvae feed on evergreen trees and shrubs. Their numbers are usually kept in check by birds, predatory insects, and (I would imagine) landings on inappropriate forage plants.
Bagworm: Thyridopteryx ephemeraeformis. University of Florida, Entomology and Nematology, Featured Creatures, Bagworm.
Bagworm. PennState Extension. 2017 Feb 28.
Drees Bastiaan M, The Texas A&M System, AgriLife Extension, E-1802 7-08.
Austin George T, Scientific Note: Moth Community from a Northcentral Florida Location – a Taxonomic Checklist. Moths recorded at 2004 SE 41st Avenue, Gainesville, Alachua County, Florida… between 2005 and 2009.
Wollerman Edward H, Bagworm. Forest Pest Leaflet 97. Forest Service, U.S. Department of Agriculture. 1971 Dec.