I thought at first that these tiny (1.3 mm length) objects might be spores from the artillery fungus, in the genus Sphaerobolus. Artillery, or shotgun, fungus is a type of primitive plant that grows as a saprophyte on wood mulch. It has tiny black spores that it can shoot for several yards. The spores are sticky and adhere to a variety of surfaces, like walls of homes, sometimes leaving a stain when removed. But, according to the submitter there was no mulch nearby, and according to my plant pathologist friend, Dr. Kevin Ong, the specimen I was looking at under my microscope was not smoothly round as typical for Sphaerobolus.
|These tiny, 1.3 mm, seeds from the Oxalis plant are sometimes|
ejected from the plant and stick to man-made surfaces, like
exterior walls, where they may be confused with "bugs".
One entomologist who wrote back noted that he once got a series of calls from a commercial greenhouse grower who was doing his best to "kill" these "pests" "crawling" all over his greenhouse, but with little success. This is another example of why it is so important to identify the pest before reaching for the insecticide sprayer.
As it turns out, Oxalis seeds are pretty cool. They are borne by the plant in a cylindrical pod. When mature, or when the rip seed pod is touched, it shoots out the small seeds three to five feet. The rough coats on the seeds helps them stick to some surfaces (like a hardy-board exterior wall, in this case). For a good video showing how Oxalis seed dispersal works, check this out. The plants themselves are attractive, if sometimes difficult to eradicate from your yard. The plant leaves are sour-tasting because of the presence of oxalic acid; but in small quantities are good in salads.
So let's not be quick to blame insects for those strange objects that customers are prone to find around the home. If you don't know what something is, have it checked out by me (if you're in Texas) or one of the other fine entomologists most states (and many pest control companies) are blessed with. There are enough real insects in the world to keep all of us entomologists busy full-time.