Aging Bed Bug Infestations: How Long Have They Been Here?

Columns - Tech Talk

January 14, 2016

Answering questions is important to customer satisfaction when resolving any pest issue, but bed bug services often involve increased urgency and emotion. How many times have you answered questions such as, “Are these bed bugs?” “Where did they come from?” “How do you treat them?” “How can I keep from bringing them home?” or “Why does my spouse get bitten, but not me?” While the answers to some questions may be simple, others are more complicated or may not have definitive answers at all. Beyond that, some answers have serious implications.

One question is, “How long have these bugs been here?” Your answer can determine more than just peace of mind. It may be used to determine fault, assign responsibility for treatment, justify accusations of treatment failure, result in litigation and more. How can one determine the length of time that has passed since the bugs arrived? Is it even possible?

For large or long-time infestations, it becomes unrealistic to determine the age of the infestation by observation alone. Confounding variables such as multiple introductions, feeding frequency and treatment attempts enter into play. It is best to say they have been there for a long time (months or years), and leave it at that. However, the age of small infestations can be gauged fairly well for the first couple months, and that is likely sufficient in many cases. Examination of the evidence may provide the answer to the following: “Were the bugs present before the customer spent the night at the hotel?” “Did the technician overlook treating this harborage, or is it a new introduction?”

*For a theoretical population starting with five adults (2 males, 3 females), two eggs per female per day, no mortality, regular blood meals, and at room temperature (72°F).

The black fecal spots and stains bed bugs leave behind are well-known signs of infestation, but do they tell time? How much spotting does a bed bug produce from a blood meal? It may be tempting to guess at age by estimating the amount of fecal spotting. However, fecal material is more a measure of how much bugs have fed than how long they have been there. Bugs may not always get a full meal or feed regularly, or the evidence can be dispersed. Therefore, only generalities should be pulled from this evidence. Little spotting could mean little feeding or a short time of infestation.

A GOOD GUESS. At normal room temperatures (72°F) and with ample feeding opportunity, bed bug nymphs require about a week for development of each instar between molts. Each molt leaves behind exuviae, the “shed skin.” In small infestations, these exuviae can be used to estimate a timeline. This method is limited, but can be useful under the right circumstances. For example, if a fourth instar bug is found alone in a mattress tuft along with some fecal spotting and three graduated exuviae, a reasonable guess would be that it has been using that harborage for at least two to three weeks.

Eggs take about 10 days to hatch at 72°F, so if you find hatched eggs attached to furniture, they’ve been there for at least that long. Newer eggs can be collected, and upon hatching provide an estimation of when they were laid.

Often a great indicator of how long an infestation has been around is the number of adult bed bugs present. Generally it takes at least seven weeks for a bed bug to grow from an egg to an adult, so there should be no new adults from eggs during that period. Therefore, if many adult bugs are present one can reasonably assume that the infestation has been there for more than seven weeks. The assumption here is that the infestation started from only a few bugs and there have not been additional introductions during that time. For example, if an infestation starts with five bugs of any stages, there will still be no more than five adults seven weeks later (see figure above).

The bottom line is that while there isn’t a surefire way to determine the age of an infestation, you can determine some limits and perhaps answer the question enough to satisfy a customer. It requires careful inspection of the available evidence including fecal spotting, exuviae, eggs and adult bugs.

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The author is the technical director and staff entomologist at Varment Guard Environmental Services/ProGuard Commercial Pest Solutions, Columbus, Ohio.