From dawn to dusk, bed bugs remain mostly in their harborages. Understanding their movements after the lights go out can provide useful insights in respect to monitoring and management.
Bed bugs were marked with hobby paint.
Like cryptic “couch potatoes,” bed bugs lead rather sedentary lives — at least during the daytime, when inspections and treatments are typically performed. Drawn by aggregating pheromones, bed bug nymphs and adults spend most of their time clustered in hidden harborages where mating, egg-laying, hatching, molting, digestion and defecation occur. They venture out in search of blood when hungry, and typically, at night.
Running on Empty. Bed bugs are mostly nocturnal, but will adapt to the sleep cycle of their host. For example, if a person works the night shift and sleeps during the day, the bugs will adjust and feed during daylight hours. Hungry bed bugs may feed regardless of the time of day — an occupational hazard experienced at times by service technicians. Hungry bed bugs also tend to move around more than satiated bugs, presumably in order to locate a food source. However, if host absence is prolonged (as might occur in a vacant apartment), their search activity may be reduced in order to conserve energy (Romero et al. 2010).
Previous studies by our group showed that bed bugs can cover a lot of ground during their nocturnal forays (Haynes et al. 2008). Video recordings of adult bed bugs in laboratory test arenas showed they can travel over 16 feet in five minutes, even in the absence of host-orienting cues. Given that the hunt for a meal could last for hours, it is understandable that wandering bed bugs can sometimes end up in suitcases and other belongings.
Field Study. Recently we had an opportunity to study bed bug movement in a heavily infested house and an apartment. Interceptor-style (pitfall) monitors were placed in several locations, near and far from where occupants slept and bugs were observed. Most of the pitfall monitors were placed along baseboards and in corners of rooms — rather than beneath bed and furniture legs — which is more typical in commercial practice. Three different kinds of monitors were used: 1) ClimbUp standard all white Insect Interceptors (Susan McKnight Inc.); 2) ClimbUp BG Interceptors having a blackened exterior edge; and 3) Blackout BedBug Detector all-black monitors offered by Protect-A-Bed.
(Top) The blue bed bugs were under a recliner (in a screw hole), while those marked with red (Image bottom) were on a sofa.
To further assess bed bug mobility, groups of bugs in various locations were marked with paint. Different colors were used to distinguish where the bugs initially resided vs. where they were subsequently found. Tiny dabs of hobby paint were applied to the dorsum of individual bed bugs with a brush (see top photo). Most of the bugs marked were adults or late-stage nymphs.
Each dwelling was re-inspected a week after the bugs were marked and monitors installed. The number of bed bugs captured in each monitor was recorded along with where marked bugs were found relative to their previous location.
Case Study #1. This small house in Frankfort, Ky., had one of the worst bed bug problems we have encountered. The infestation was so severe that bugs were living on one of the two occupants. Bed bugs were most noticeable in the living room, where the couple had been sleeping for several months. Before beginning our monitoring, two heavily infested couches and a recliner were removed from the living room and placed outdoors by the occupants. Large numbers of bed bugs remained present on living room walls, curtains and other furnishings, including the recliner where one individual continued to sleep throughout the study. The other occupant decided to vacate the dwelling.
Fifty-one pitfall-style monitors were placed throughout the home, mostly along baseboards and in corners of rooms. In some locations, different types of monitors were placed side by side to compare capture efficiency. Groups of bed bugs also were marked in selected locations with different paint colors, in order to help track subsequent movement. Bed bugs residing on three sets of window curtains in the living room were marked either with red, green or yellow (see images below), while those aggregating on the recliner were marked blue. Bugs congregating near the front entry door, along the baseboard and items on the floor were marked with pink paint, while a small aggregation diagonally across the living room in a corner of the ceiling were marked with white.
Observations. A total of 462 bed bugs were captured in pitfall monitors throughout the home one week after installation (see Figure 1 above). Although more bed bugs were caught in the living room where the occupants slept, many bugs were captured elsewhere — even in the kitchen and bathroom — noteworthy, considering that no bed bugs were spotted in these areas during our initial, visual inspection.
Marked bed bugs were most prevalent in their originally documented locations (see Figure 2 above). After one week, half of the bugs marked with green paint (15 of 30) were found on the same set of living room curtains. Twenty-four percent of those marked with red paint (12 of 50) were observed on curtains initially receiving red, and 10 percent of the bugs marked with yellow (2 of 20) were noted on curtains designated by yellow. Ten percent (5 of 50) of blue-marked bed bugs were spotted a week later on the same recliner.
However, several marked bed bugs were also discovered in areas other than where they were previously marked. For example, five red bed bugs and a yellow one were found on curtains marked “green” — while a blue-marked bug (formerly on the recliner) and a pink one (originally on the floor by the front entry), were found on curtains marked “red.” Other interesting finds included a red-marked bed bug in a pitfall trap in the long vacated bedroom at the other end of the house more than 30 feet away; and a pink and a red bed bug recovered in monitors on the opposite side of the living room about 15 feet away. Movement of marked bed bugs in buildings has also been observed by Cooper and Wang (personal communication).
Case Study #2. The second evaluation involved an apartment located on the ground level of a four-unit rental property in Lexington, Ky. The apartment was severely infested and had an abundance of clutter. Both occupants slept on sofas in the living room since the bedrooms were filled with boxes and belongings. Neither tenant said they were being bothered or bitten by the bugs and chose to remain in the dwelling. As expected, most bed bugs were noticed in the living room where the occupants slept. Large numbers were present on the two sofas, a recliner and the walls and floors.
White and black-sided ClimbUp Insect Interceptors were installed side-by-side along baseboards in 11 different locations of the apartment. Groups of bugs in selected locations also were marked with paint as previously described. Bed bugs on one side of the sofa nearest the kitchen were marked with pink paint, while those on the other side of the sofa were marked with yellow. Bugs residing on the wall behind were marked blue. Bed bugs across the room on the other sofa were marked red, on the recliner white and on the wall behind green.
Observations. A total of 453 bed bugs were captured in pitfalls throughout the apartment after one week (see Figure 3 above). As expected, the majority were caught in the living room where both occupants slept. Bed bugs also were found in monitors elsewhere in the apartment even though none were seen in these areas during the initial inspection. Both black- and white-sided ClimbUps captured similar numbers of bed bugs (17.1 vs. 16.3, respectively).
Marked bed bugs were again most prevalent in their originally documented locations (see Figure 4 above). After one week, 25 percent of those marked with pink paint (25 of 100) and 25 percent of those marked with yellow paint (16 of 65) were found in their original sofa locations. Surprisingly, only three percent (3 of 100) of blue-marked bugs were observed in their original location on the wall behind that sofa. On the other side of the room, 18 percent (18 of 100) of red-marked bugs were found in their original location on the other sofa. On the wall behind that sofa and an adjacent recliner, 18 percent (8 of 45) of green-marked bugs still resided in their original location. On the recliner, 45 percent (30 of 67) of previously white-marked bugs were recovered on the same item of furniture.
Several marked bugs were again discovered away from originally marked locations. For example, six blue bugs formerly on the wall nearest the kitchen moved onto the adjacent sofa, while two pink and one yellow bug moved from sofa to wall. On the other side of the room, seven green bugs from the adjacent wall moved onto the sofa — whereas a couple of pink bugs moved from one sofa to another — or to the wall on the opposite side of the room. Four pink and one yellow were found in a pitfall trap on the floor adjacent to the couch where they were originally marked. Three blue bugs from the adjacent wall were also found in that trap. A single red bed bug was spotted in a pitfall behind the sofa, the only one discovered away from its original marked location. No white-marked bed bugs, formerly on the recliner, were found elsewhere in the apartment.
Lessons Learned. These examples clearly reinforce that bed bugs move around during their nighttime forays. In each infested dwelling, many bugs were found in pitfall traps away from where occupants slept, and/or were spotted in different areas from where they were previously marked. Similar findings were reported by colleagues at Rutgers University (Wang et al. 2010, Wang and Cooper 2012). It should be noted that both infestations were well established, and that the degree of movement might differ with smaller populations.
Bed bugs congregate near sleeping or stationary hosts, especially during early stages of infestation. As populations grow larger, they often disperse beyond the usual beds, sofas and recliners to other areas of refuge. Why this happens is still under investigation. One theory is that bed bug dispersal is initiated by adult females seeking to avoid repeated, potentially harmful mating attempts by males. Another hypothesis is that dispersal has little to do with “fleeing” females, and has more to do with refuge availability. Rather, as numbers increase and harborages near hosts become occupied, bed bugs (comprised of all life stages) gradually form new clusters farther away.
Another question researchers are attempting to answer is whether blood-seeking bed bugs return to their former harborage locations. In instances where we marked known numbers of bed bugs, 3 to 50 percent of them were observed one week later in the same general area. Only a few paint-marked exuviae (shed skins) were recovered from late-stage nymphs that had subsequently molted. Bed bugs probably feed at least weekly in the presence of a host. Finding many marked bugs the following week in the same general area could reflect a degree of harborage “fidelity” or “faithfulness” after feeding — or not — since we cannot be certain the bugs ever left.
Many bed bugs were captured in pitfall monitors throughout the dwellings.
No clear differences were observed between pitfall designs and their capture effectiveness. Blackout traps and black-sided ClimbUp BG traps caught similar numbers of bed bugs in eight paired comparisons (11.1 vs. 13.8, respectively). Black ClimbUps also were similar to white ClimbUps in 15 paired comparisons (17.1 vs. 16.3, respectively). Clearly more study is needed under different test designs and conditions, but our results give us no reason to recommend one pitfall trap over another based on their efficiency. We did not collect data on capture and retention of different bed bug life stages (including young nymphs). Because our sample sizes were small, further study is needed to determine whether color affects capture rate under field conditions.
In the meantime, each pitfall-style monitor we used was effective at capturing and revealing the presence of bed bugs, including in areas away from the human hosts. This was true even when stations were placed along baseboards and areas other than beneath the legs of beds and sofas. Consequently, pest managers may want to expand their thinking when using such devices. If conditions preclude installing monitors directly under bed and sofa legs, try placing them adjacent. Also consider placements along baseboards (especially behind sleeping and seating areas), and in corners of rooms. Installation of pitfall devices along hallways and room perimeters (Wang et al. 2010, Wang and Cooper 2012) also may reveal a continued presence of bed bugs in vacant dwellings where removal of furnishings has made visual inspection less reliable.
Pest managers are discovering — often the hard way — that absence of bed bugs during a visual inspection is no guarantee that none are present. The industry has been down this rocky road before with termite inspections. Thorough inspection is advisable given that bed bugs do move about within dwellings…and remember to be careful what you promise.
All photos copyrighted by the authors. Financial support for this study was provided by Rollins Inc.
Michael F. Potter is a Provost’s Distinguished Service Professor at the University of Kentucky. Jennifer R. Gordon and Mark H. Goodman are Ph.D. students at the same institution. Travis Hardin is service manager of OPC Pest Control in Lexington, Ky.
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