ovisacs

Ovisacs are protective structures that enclose eggs in certain invertebrates, most commonly arthropods such as spiders, mites, and some scale insects. An ovisac is produced by the female using specialized glands and secretions, and may be made of silk, wax, or other materials. Ovisacs can be carried by the female, attached to vegetation, or deposited on a substrate, and they vary widely in size, shape, and texture among species.

The primary function of an ovisac is to protect developing eggs from desiccation, predation, and environmental stress, while often providing a stable microenvironment for embryonic development. In many spiders and some mites, eggs mature inside the sac and hatch within or soon after the sac is opened. In other insects, such as certain scale insects, the ovisac contains multiple eggs that are released when the sac is opened or consumed.

In taxonomic and ecological studies, ovisac characteristics such as size, wall composition, and attachment method can be used to help identify species and infer reproductive strategies. The term is sometimes used interchangeably with egg sac, although some authors reserve ovisac for sacs with particular structural properties or origins.

Overall, ovisacs illustrate a common evolutionary solution among terrestrial invertebrates for protecting eggs during the vulnerable early life stage and for facilitating egg dispersal.