Insect Word of the Week: FRASS

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Doo-Doo, dung, excrement, feces, manure, guano, poo or poop… it is helpful to know all the functional words for excrement, and not just for "Sh..." oh wait a minute,  "Frass and Giggles".


FRASS is a term used by entomologists for insect excrement.  You may run across the term in books, factsheets, or on bygl alerts because frass is more than a fun term to throw around.  It can be: a helpful diagnostic indicator, involved in unique insect behaviors and survival adaptations, be the vector of disease or a nutrient source for others. So, let’s DIG IN.


In Borror and Delong’s "Introduction to the Study of Insects", frass is first defined as a combination of the plant debris made by wood-boring insects mixed with their excrement (Triplehorn & Johnson, 2005, p. 785). The sawdust-like waste that is pushed out from bore holes is often a first sign of wood infestation by wood boring insects such as ambrosia beetles, powderpost beetles or Asian longhorn beetles (Anoplophora glabripennis).




ambrosia beetle feeding is easily identifiable by the toothpick frass that sticks out from the side of an infected branch

if you notice sawdust around a beam, log, or other wood item, it may be a sign of powder post beetle infestation

Asian Longhorn beetle, a non native invasive, leaves large wood shavings as frass

Often we find frass still inside the galleries, or tunnels, made by wood boring insects.

Often we find frass still inside the galleries, or tunnels, made by wood boring insects.



And our word of the week definition could stop there, BUT! as with so many words in our vernacular, the use of the word FRASS has expanded beyond the narrow definition above to now be colloquially used to define just about any insect’s solid excrement like the caterpillar frass below. 



Herbivorous insects can produce copious quantities of waste products that can easily give away their presence. The herbivore may be well hidden, but the piles of frass are not. While out in the garden, if you spot an accumulation of frass like this, you may want to spend some time scouting for the producer of the excrement somewhere above the pile of frass.





Milkweed tussock moth caterpillars are heavy feeders on milkweed plants




These Milkweed Tussock (Euchaetes egle) caterpillars were hard to miss with their brightly colored and showy fluff. This milkweed was covered with them munching away with the frass piles to prove it. However, other caterpillars might be more camouflaged such as a green tomato hornworm, Manduca quinquemaculata blending in with the tomato vines or these bagworms, Thyridopteryx ephemeraeformis, which cover their bags with plant debris. Bagworms often go unnoticed, disguised in cocoons that resemble cones from afar, especially when attached to evergreen trees. Their feeding damage and frass buildup can therefore be a helpful clue to look closer at those mysterious bags hanging from the tree.



bagworms can defoliate  trees quickly

during heavy feeding by insects, frass may build up on the branches of trees and shrubs as shown here

The general public cannot always distinguish insect droppings from plant material. Here the bagworm poop is blending in with the dried needles of the arborvitae.



Frass can be such a good indicator of the presence of an insect that some species actually YEET their poops far away to prevent attracting predators. This is especially important to deter predators and parasitoids that hunt by scent. Here is a video of a caterpillar flinging poo from Purdue University (LINK).




Frass in Diagnostics

Frass may be a helpful indicator in the diagnosis and management of pests.



Example 1


I received a call from a farmer concerned he had crown gall in his blackberries. Canes had gall-like bulges around where canes were snapping as you see below.




photo showing signs of red neck cane borer which at the time was a mystery to diagnose

Additional symptoms of a blackberry cane issue

swollen cane of blackberry



At first glance, you might think disease, but upon closer examination, we found what looked like tiny, curled wood shavings on blackberry leaves. This is insect frass from an insect boring in the canes.




tiny wood shavings shown in photo are frass found on the leaves are an indication of insect boring




This suggested insect activity, but was it necessarily related to these symptoms or something else? Remember that a plant can have multiple problems happening at once. Further inspection revealed a borer exit hole in the cane. Upon splitting it opon we found frass inside. These symptoms line up with feeding damage from boring pests like Redneck Cane Borer, Agrilus ruficollis or Common Stalk Borer, Papaipema nebris. We sent stalks into the C. Wayne Ellett Plant and Pest Diagnostic Clinic ( to ensure nothing else was afoot (there wasn’t). The discovery of the frass helped lead us to management decisions to prune out the swollen and lodged canes to destroy overwintering larvae and a plan to scout in May-June for adults of redneck cane borer next season (See the Midwest Fruit Pest Management Guide for more on cane borer management).



red neck cane borer exit hole and frass in the cane




Example 2


Pines are notorious weepers. Pine trees ooze resins when they’re pruned, around budding, during season changes, and when sap begins to run. But when is it too much? How can we know if it a problem?  One thing to look for, is FRASS.




oozing sap from pines, mixed with insect frass, can be a sure sign of zimmerman pine moth feeding

flecks of color and wood particles in pine sap indicate insect feeding inside the trunk



IF you find a large waterfall of sap or a ball of ooze building up, check the resin for frass. Look for wood shavings on the outside or mixed in. Is the sap golden or muddied with material? If frass is present, this may be a sign of Zimmerman Pine Moth (Dioryctria zimmermani) feeding. This caterpillar bores under the bark of a tree, often at a branch collars, causing excess oozing from the wound.  It can cause considerable damage to Austrian and Scots pine, and occassionally on Douglas Fir and spruce too. For more information on Zimmerman Pine Moth click here.


Example 3


white pine weevil leaves alot of frass in the galleries in the dead tip of the tree


White Pine Weevil-WPW- (Pissodes strobi) feeds in the terminal shoot of pines and spruces in Ohio. WPW feeding causes the central leader of these evergreens to turn brown and curl into a “candy cane” hook. One management strategy to attempt to reduce WPW populations is to cut the infested leader off and train a new side branch to become the new central leader. But where do you make the cut???  FOLLOW THE FRASS!  Frass can show you how far down the damage/feeding has occurred. If we prune beneath this damage at the right time of year, it may reduce next year’s population by removing the cocoons of next season's weevils. Coupled this pruning with timely application of appropriate insecticides, growers may even prevent re-infestation in the next season.  For more on WPW management click here.




SMOKE AND MIRRORS: Frass Disguises 



Several insects use frass to camouflage themselves from predators. This tortoise beetle larva holds its frass and cast skins on a pair of cerci it folds over its back, supposedly to prevent being eaten.  I don’t look good, I don’t smell good, don’t eat me!



frass covered tortoise beetle avoiding predation



Below are sumac flea beetle larvae (Blepharida rhois).  These are protected by their poo from egg to adulthood. The female covers her eggs in a “fecal shield” to protect them from predators like ants. The newly emerged larvae also begin to cover themselves with poo protection. One study found that the frass was protective only if the larva was feeding on its host plant, sumac. When the larvae were fed only lettuce, predatory ants easily attacked the larva (Vencl & Morton, 1998), suggesting the frass retained some chemical defense from the host plant that then benefited the insect. 



insects, especially larva and immature nympths, may cover their body with frass to prevent predation



Chemicals in frass can act as deterrent or attractant. Frass may not only attract predators but, in some cases, frass may attract fellows of the same or even related species.



Is Honeydew considered frass? Maybe?

You may also be familiar with another type of insect waste known as "honeydew". While the term FRASS is normally reserved for solid waste, honeydew is a sugary liquid waste.  It is excreted by phloem-feeding hemipteran insects such as aphids, psyllids, mealybugs, planthoppers, leafhoppers, and scale insects.


some scale insects are hard to find but you may find their honeydew first. droplets of sugary sap fall from sap feeders.

honeydew appears wet, shiny, and sticky on the surface of other plants when it drops from the feeding insect's behind. Sooty mold can grow on the honeydew and other insects eat it too.


In order for insects to receive the needed nutrient benefit from their host plant, they consume large volumes of sap of which up to 90% of the ingested sugar is concentrated and evacuated as waste (Douglas, 2009). To prevent being smothered by their own waste, some species mix waxy secretions with the sugary waste until it crystalizes (becoming a substance known as LERP) and many species can throw the honeydew droplets away, resulting in rain-like droplets falling from trees and speckling our lawn furniture, hardscape, and understory plants like the hosta leaves above. Ants are common harvesters of honeydew droplets. Other insects may feed on honeydew buildup such as wasps and butterflies. Fungus known as sooty mold can also grow on the honeydew droplets. While not infecting the leaf surface, the build up of sooty mold can negatively affect a plants ability to receive sunlight exposure.


More than waste!


We've shared that frass may help with our diagnostics, helps protect insects, other organisms might grow off or feed on this waste... but lastly I'll share that frass may now be big business. Entrepreneurs have begun looking at uses for frass as nutrients. For example, the journal, Frontiers in Sustainable Food Systems has a whole section of articles devoted to "Frass: the legacy of larvae" describing research on insect frass as fertilizer. And indeed I have found insect frass sold as organic fertilizer. The organic fertilizer is composed of black soldier fly larva frass. The black soldier flies are reared as food for birds. The larvae are fed vegetable matter. As they feed on the vegetables, their frass accumulates in their cultures. The waste product from one enterprise has become an enterprise of its own. And the frass sells for $10 a pound for a fertilizer with a 2-2-2 nutrient analysis. That’s some expensive frass!  One master gardener at least was pleased with the results!


Insect frass is being harvested for fertilizer





Triplehorn, C. and Johnson, N. (2005). Borror and Delong's Introduction to the Study of Insects. 7th edition.  Thompson Brooks/Cole publishing.

Douglas, A. (2009). Honeydew IN The Encyclopedia of Insects. 2009. 

Vencl, F. and Morton, T. (1998). The Shield Defense of the Sumac Flea Beetle, Blepharida rhois (Chrysomelidae: Alticinae). Chemoecology. 8. 25-32.