The lac bug, scientifically known as Kerria lacca, is a small, scale insect belonging to the family Kerriidae, primarily recognized for producing a valuable natural resin called lac. This resin is the sole raw material used to create shellac, a natural polymer with diverse commercial applications. The process of harvesting and refining this resin involves an intersection of insect biology and human processing. This article explores the life cycle of the lac bug, the composition of its resin, and how this unique substance is transformed into shellac.
Classification and Biology of the Lac Bug
The lac bug is a sessile, reddish-brown insect that spends most of its life attached to the branches of specific host trees, such as the kusum, palas, or ber tree. It is classified within the order Hemiptera and the superfamily Coccoidea. The insect’s life cycle begins with the egg, which hatches into the first-instar nymph, a mobile stage known as a “crawler.”
The crawlers disperse across the host plant and settle on new twigs, inserting their piercing-sucking mouthparts into the tree’s phloem to feed on the sap. Once settled, the female nymph becomes immobile and begins to secrete a protective, resinous coating from specialized glands. The female insect is responsible for the vast majority of lac resin production, forming a hard, scale-like covering that envelops her body. The life cycle typically spans about six months, after which the female dies inside her protective resin chamber.
The Source Material: Raw Lac
The resinous substance secreted by the lac bug is known as raw lac, or sticklac. This material forms a thick, encrusted layer around the host tree’s branches, creating a composite crust of resin, insect bodies, and twigs. When the lac is ready for harvest, farmers cut or scrape the resin-coated branches from the trees.
Lac cultivation is largely concentrated in tropical and subtropical regions of Asia, with India and Thailand being the largest producers. The harvested sticklac is a crude mixture, containing resin, insect remains, wax, and fragments of the host plant. The raw material must be crushed and sieved to remove impurities, resulting in a granular product called seedlac. Seedlac is the intermediate product ready for the final refining steps to create shellac.
Shellac and Its Primary Uses
Shellac is the final, purified form of lac resin, produced from seedlac through either heat treatment or solvent extraction. In the heat method, seedlac is melted and squeezed through a filter cloth to separate the pure resin from impurities. The molten, filtered resin is then stretched into thin sheets that become brittle upon drying, which are broken into the familiar shellac flakes.
This refined resin is a natural polymer prized for its non-toxic, moisture-resistant, and strong adhesive properties. Its most traditional application is as a wood finish, providing a durable, glossy, and protective layer. It is widely used in the food industry as a glazing agent for confectionery, such as candies and chocolates, designated as food additive E904.
The pharmaceutical industry relies on shellac as a coating material for tablets and capsules. The resin forms a protective barrier that shields the drug from environmental factors like moisture and light, helping maintain potency. Shellac is often used to create enteric coatings, designed to prevent a tablet from dissolving until it reaches the small intestine.