A few weeks ago i received a call from a customer who believed she had ants in her pantry.  Now to give Mrs X credit, she had very recently lost her husband and is on quite a few medications, but what I found in her pantry was most definitely not ants.  Instead, it was a few thousand of these:

For those of you who do not know, this is Stegobium paniceum, better known as the drugstore beetle or biscuit beetles if you are in the U.K.  These tiny bugs are cylindrical, 2.25 to 3.5 mm long, are all a uniform brownish red (or reddish brown) color with longitudinal lines of pits and hairs on the wing covers, or as we in the business call them, elytra.  not visible in this picture are the 3 clubbed antenna usually found on this critter.
The life history of the drugstore beetle is as follows:  Females lay as many as 75 eggs in or near a food source.  The egg hatches into a white c shaped larvae.  The larval period lasts from four to twenty weeks depending on temperature, availability and quality of food source.  The larvae spend this time tunneling through the food substrate (flour, spices, damn near anything really) until they molt several times and reach full grown larval stage.  They then build a cocoon and enter a non feeding resting state called a pupa.  in the cocoon they transform over a period of 12 to 20 days into an adult beetle.  Adult beetles do not eat.  The females live approximately 12 to 65 days.

They can be a difficult pest to deal with for a few reasons.  They eat and infest anything from any spice in your cabinet to dog biscuits to prescription drugs to, well, you name it, including but not limited to birds nests, seeds, cookies, will bore into books, leather, and wood.  You must find and remove any and ALL infested products.  This is not always as straight forward as it seems,  I, for example, had a multiple callback situation where every time I thought I had them killed off more would appear.  In this case, rats (already eliminated) had carried off some dog food and bird seeds and stashed it in the wall where these guys were breeding.  It was driving me nuts.  Finally I noticed some crawl out from under the baseboard.  I dusted the crack and crevice along the baseboards in the pantry with Delta dust and problem solved.

So, in summation, if you find these in your home or your customers home, step one is seek out the source of the problem and eliminate it from the house.  Vacuum up as many as you can and throw away the bag or dump the bin immediately and dispose of outside. If the situation warrants it treat the cracks and crevices with a non residual knock down product such as CB80, 565, or the like.  Read any product label carefully before applying it to make sure that 1) product can be used on the pest you want to kill, 2) product can be used in the location you want to kill said pest, 3)how long do you or the homeowner need to stay out of the treated area (re-entry period), and 4) what, if any, clean up measures should be taken by you or the homeowner after re-entry.