Jun 1, 2012 – Frass In Many Forms
QUESTION:
Yesterday I inspected a log home and found this very fine frass everywhere falling from the ceiling and hanging from spiders' webs. A lot of acrobat ants were present in trails in several areas in the home as well. Inspecting the structure also showed what looked like evidence of ambrosia beetle damage with the blue to black staining on the wood on walls and cross beams. My question is, could the frass be from the acrobat ants or the beetles? No evidence of beetles was found anywhere in the structure, some mold was present on the cross beams, and water damage was present in the top of the structure.
ANSWER:
It would be very important to gather some of that "frass" and take a very close-up look at it, preferably through a dissecting microscope that allows you to see details. The term frass refers either to fecal material that wood-eating insects like beetles might produce, or to sawdust and wood debris created by insects like ants, that do not eat the wood but which excavate cavities and then keep them cleared by pushing out unnecessary debris. Fecal pellets are going to have a more defined shape and would be more compact and oval, whereas sawdust frass has a haphazard look to it and obviously has not been run through the bug's system. Quite often, if it is frass from ants, you also will find other things in the mix. Carpenter ants are the classic WDO ant, and within the frass you often find pieces of other insects that they fed upon, parts of dead ants that died within the colony, and white silk pupal cases that were no longer needed once the adult ant emerged. I once was handed a jar of "frass" that kept appearing near a fireplace, and to the naked eye it looked like dirt but under good magnification was clearly hundreds of dead ants.
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Yesterday I inspected a log home and found this very fine frass everywhere falling from the ceiling and hanging from spiders' webs. A lot of acrobat ants were present in trails in several areas in the home as well. Inspecting the structure also showed what looked like evidence of ambrosia beetle damage with the blue to black staining on the wood on walls and cross beams. My question is, could the frass be from the acrobat ants or the beetles? No evidence of beetles was found anywhere in the structure, some mold was present on the cross beams, and water damage was present in the top of the structure.
ANSWER:
It would be very important to gather some of that "frass" and take a very close-up look at it, preferably through a dissecting microscope that allows you to see details. The term frass refers either to fecal material that wood-eating insects like beetles might produce, or to sawdust and wood debris created by insects like ants, that do not eat the wood but which excavate cavities and then keep them cleared by pushing out unnecessary debris. Fecal pellets are going to have a more defined shape and would be more compact and oval, whereas sawdust frass has a haphazard look to it and obviously has not been run through the bug's system. Quite often, if it is frass from ants, you also will find other things in the mix. Carpenter ants are the classic WDO ant, and within the frass you often find pieces of other insects that they fed upon, parts of dead ants that died within the colony, and white silk pupal cases that were no longer needed once the adult ant emerged. I once was handed a jar of "frass" that kept appearing near a fireplace, and to the naked eye it looked like dirt but under good magnification was clearly hundreds of dead ants.
If this is a beetle infestation the most likely culprits would be deathwatch or furniture beetles in the family Anobiidae. Their fecal matter is dry and loose and falls from the feeding galleries through the exit hole of the adult beetles. However, you then should be able to find lots of small, round holes in the wood above where this frass is occurring. As far as the possible evidence of ambrosia beetles, if this is being seen on the surface of the finished wood then it more likely is just old feeding galleries that were present when that wood was milled for lumber, and the galleries within the wood were exposed when the saw moved across them. It would be against the nature of any of the wood eating beetles to feed on the surface of the wood, and ambrosia beetles actually feed on a fungus that is cultivated within the channels in the wood.
I suggest starting with that careful ID on the frass itself, determining if it is fecal pellets or sawdust. Then you can proceed with a more careful inspection once you know it is either beetles or ants creating it. While carpenter ants are the most common group causing damage in wood, other kinds of ants could also enlarge cavities they find and push the sawdust out. In the western U.S. we have the common "black velvety tree ant" that is extremely common in forested areas of the mountains, and which is the culprit when large piles of sawdust are accumulating on window sills and floors.
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