Pruinescence , or pruinosity, is a "frosted" or dusty-looking coating on top of a surface. It may also be called a pruina (plural: ''pruinae''), from the Latin word for hoarfrost. The adjectival form is pruinose .
Entomology
In insects, a "bloom" caused by wax particles on top of an insect's
cuticle
A cuticle (), or cuticula, is any of a variety of tough but flexible, non-mineral outer coverings of an organism, or parts of an organism, that provide protection. Various types of "cuticle" are non- homologous, differing in their origin, structu ...
covers up the underlying coloration, giving a dusty or frosted appearance. The pruinescence is commonly white to pale blue in color but can be gray, pink, purple, or red; these colors may be produced by
Tyndall scattering
The Tyndall effect is light scattering by particles in a colloid or in a very fine suspension. Also known as Tyndall scattering, it is similar to Rayleigh scattering, in that the intensity of the scattered light is inversely proportional to the ...
of light. When pale in color, pruinescence often strongly reflects ultraviolet.
Pruinescence is found in many species of Odonata, particularly
damselflies
Damselflies are flying insects of the suborder Zygoptera in the order Odonata. They are similar to dragonflies, which constitute the other odonatan suborder, Anisoptera, but are smaller and have slimmer bodies. Most species fold the wings along ...
of the families Lestidae and Coenagrionidae, where it occurs on the wings and body. Among true dragonflies it is most common on male
Libellulidae
The skimmers or perchers and their relatives form the Libellulidae, the largest dragonfly family in the world. It is sometimes considered to contain the Corduliidae as the subfamily Corduliinae and the Macromiidae as the subfamily Macromiinae. Ev ...
(skimmers).
In the
common whitetail
The common whitetail or long-tailed skimmer (''Plathemis lydia'') is a common dragonfly across much of North America, with a striking and unusual appearance. The male's chunky white body (about 5 cm or 2 inches long), combined with the brown ...
and blue dasher dragonflies (''Plathemis lydia'' and ''Pachydiplax longipennis''), males display the pruinescence on the back of the abdomen to other males as a territorial threat. Other Odonata may use pruinescence to recognize members of their own species or to cool their bodies by reflecting radiation away.