Scale

Definition

A flattened, plate-like integumentary structure that is an outgrowth of a single cell or cell group, typically secreted by the epidermis and often overlapping like shingles. In insects, scales are most abundant on wings of Lepidoptera, where they create color patterns through pigmentation and structural interference; they also occur on bodies of some Collembola and other groups. In arachnids, scales appear as decorative or sensory setal modifications on legs and pedipalps of some spiders and solifuges. Scales differ from macroscopic sclerotized plates (tergites, sternites) by their microscopic origin and often detachable nature.

Etymology

Middle English scale, from Old French escale, of Germanic origin; akin to Old English scealu, shell, husk

Example

The wings of a monarch butterfly (Danaus plexippus) bear approximately 0.1 mm-wide scales that produce its orange-and-black warning coloration; under magnification, each scale shows a single basal stalk (pedicel) anchoring it to the wing membrane.

Synonyms

• squama (pl. squamae)
• lamella (when flattened, layered)

Related Terms

• seta
• microtrichia
• Integument
• Epidermis
• Lepidoptera
• wing coupling
• structural coloration
• Ecdysis

Usage Notes

Distinguish from fish scales (dermal, mesodermal origin) and reptilian scales (epidermal but non-homologous, thicker, non-detachable). Lepidopteran scales are diagnostic for the order and are shed during eclosion and flight, leaving 'scale dust.' Specialists reserve 'scale' for these single-cell derivatives; larger cuticular plates are termed sclerites or shields. In some contexts, 'scale' also refers to the protective waxy covering secreted by scale insects (Coccoidea), but this is a separate structure derived from glandular secretions and exuviae, not an epidermal outgrowth.