Frass refers loosely to the more or less solidexcreta of insects, and to certain other related matter.
Frass is an informal term and accordingly it is variously used and variously defined. It is derived from the German wordFraß, which means the food takeup of an animal.[1] The English usage applies to excreted residues of anything that insects had eaten, and similarly, to other chewed or mined refuse that insects leave behind. It does not generally refer to fluids such ashoneydew, but the point does not generally arise, and is largely ignored in this article.
Such usage in English originated in the mid-nineteenth century at the latest.[2][3] Modern technical English sources differ on the precise definition, though there is little direct contradiction on the practical realities. One glossary from the early twentieth century speaks of "...excrement; usually the excreted pellets of caterpillars."[4] In some contexts frass refers primarily to fine, masticated material, often powdery, thatphytophagous insects pass as indigestible waste after they have processed plant tissues as completely as their physiology would permit.[5] Other common examples of frass types include thefecal material thatlarvae ofcodling moths leave as they feed inside fruit or seed, or thatTerastia meticulosalis larvae leave as they bore in thepith ofErythrina twigs.
Various forms of frass may result from the nature of the food and the digestive systems of the species of insect that excreted the material. For example, manycaterpillars, especially large, leaf-eating caterpillars in families such asSaturniidae, produce quite elaborately moulded pellets that may be conspicuous on the ground beneath plants in which they feed. In the tunnels they eat in the leaves,leaf miners commonly leave visible amorphous frass residues of the pulp of themesophyll. Their frass commonly does not fill the tunnel.
In contrast, larvae of mostpowder post beetles (Lyctus) partly eject their finely granular frass from their tunnels when boring in the wood on which they feed, while the larvae of most dry-woodCerambycidae leave their frass packed tightly into the tunnels behind them. Many other species of wood borers also leave the tunnels behind them tightly packed with dry frass, which may be either finely powdery or coarsely sawdusty. Possibly this is a defence against other borer larvae, many species of which arecannibalistic, or it might reduce attacks from some kinds of predatorymites or soak up fluids that a live tree might secrete into the tunnel.
Loose, fibrous frass of some moths in the familyCossidae, such asCoryphodema tristis, may be seen protruding from the mouths of their tunnels in tree trunks, especially shortly before they emerge as adult moths. In this respect, their frass differs from the powdery frass of powder post beetles such asLyctus.
Borer tunnels may occur either in dry or rotting wood or under bark, in the comparatively soft, nutritiousbast tissue, either dead or living.
Some boring insects do not digest the wood or other medium itself, but bore tunnels in which yeasts or other fungi grow, possibly stimulated by excretions and secretions of the insects. Such tunnels obviously cannot be permitted to become clogged, or the insects could not access their own pastures, so they must either eject at least part of their frass, or otherwise leave room for the edible growth. Examples of such boring-insect/fungal associations includeambrosia beetles withambrosia fungi, theSirex noctilio with its fungal partnerAmylostereum areolatum, and more.[6]
In a significantly different sense the term "frass" also may refer to excavated wood shavings thatcarpenter ants,carpenter bees and other insects with similar wood-boring habits eject from their galleries during the tunneling process. Such material differs from the frass residues of foods, because insects that tunnel to construct such nests do not eat the wood, so the material that they discard as they tunnel has not passed through their gut.[7] Even professional entomologists might need suitable instruments and detailed examination to distinguish this from food-derived frass.
Contact with frass causes plants to secretechitinase in response to its highchitin levels. Some frass, such as that of thefall armyworm, can also reduce plants' herbivory defenses.[8] Frass is amicrobial inoculant, in particular asoil inoculant, a source of desirable microbes, that promotes the formation of compost.[9]
Many insect species, usually in their larval stages, accumulate their frass and cover themselves with it either to disguise their presence, or as arepugnatorial covering.
.jpg)
.jpg)
