[Vertebrate Pests] Bat bugs on the bed…bed bugs on the bats?

Well, as the trite saying goes, unless you’ve been hibernating in a cave (and as you will see, caves are appropriate for this month’s discussion) bed bugs are back in a big way for many large urban areas of the country.

Bed bugs belong to the insect order Hemiptera, (the true bugs) and within the family Cimicidae. The word "Cimicid" originates from ancient Rome when the bed bug was referred to in Latin as "cimex."

The most widespread Cimicid species infesting structures in the United States are the common bed bug, Cimex lectularius and the Eastern bat bug, C. adjunctus. For many pest professionals, these two Cimicid bug groups (also including swallow bugs) are indistinguishable without magnification and using a simple key the first time or two. In the western states, the Western bat bug, C. pilosellus, occurs.

Interestingly, many scientists agree that the probable original adaptation of bed bugs began when humans moved into caves for shelter. Caves, of course, are one of the natural shelters for bats. Over time, some species of bat bugs developed the ability to feed either on the bats hanging in the cave’s ceiling, or, on the cave "men" as alternative hosts when the bats left the caves for different shelters, or when the bats were killed and/or eaten by humans.

Eventually, a close but distinct species arose — the bed bug, which engages in the complement host feeding behavior of the bat bug. In other words, the bed bug feeds on humans in buildings as its primary host and bats and some other animals as alternate hosts. Of course, what are our buildings and houses but artificial substitutes for caves?

I myself am very familiar with bat bugs. For my master’s project in graduate school, I studied bats in attics. In most of the attics I noticed bat bugs. But three particular attics contained several hundred bats and it seemed to me these attics contained "thousands" of bat bugs (all of which I later identified as C. adjunctus).

So for the purposes of this Vertebrate Pests column, the salient discussion for pest management professionals is whether or not buildings that contain bat infestations and their associated bat bugs are of much concern for the people living in the building below. Therefore, let’s examine bat bugs in greater detail.

BED/BAT BUG BIOLOGY. Both bed bugs and bat bugs have virtually the same life histories. The differences exist between their primary and alternate hosts.

According to studies on Cimicids, mated females over the course of about one week deposit six to 10 eggs several days after feeding on blood. Depending on temperature and humidity, females may feed every three to four days. The eggs are laid one at a time and contain a cement which allows the eggs to stick to various surfaces. In attics, the eggs are commonly deposited in small clusters within various crevices and joints produced where the roof rafters meet the roof sheathing. They also are found beneath the wood splinters of the rafters upon which the bats hang during the day. These are the same locations in which the nymphs and adult bat bugs also harbor when they are not feeding on the bats.

The eggs hatch from four to 12 days and the bat bugs proceed through five nymphal stages, each lasting about three to 10 days. Optimal development temperature is 86°F (30°C). The total development time for the common bed bug has been calculated to be from as little as 24 days at 86°F, and being delayed for as long as 128 days at 65°F.

At low temperatures, the nymphs may survive for five to six months without feeding. The adults can survive even longer. This is a good ectoparasite fit because bat colonies living in structures often leave buildings beginning in the autumn months for their winter hibernacula and do not return back to the nursery colony until the spring. Consequently, the bats may not be available as hosts for four to six months. (In many bat colonies, however, at least some bats begin returning at four months; and most are back in the maternity colonies within five months.)

An interesting question, but one that we don’t have many answers for, is how many bat bugs come down from the attics seeking alternate hosts when the bats either leave for the winter, or switch to an alternate roost site. We do know there are dozens of cases where bat bugs have been found to come down from the attic and feed on sleeping humans (in those upstairs bedrooms in close structural proximity to the attic). According to the ninth edition of the Mallis Handbook, 14 different infestations of Eastern bat bugs (Cimex adjunctus) have been reported in eight different states since 2000.

Bat bugs typically attack humans when a colony of bats has been excluded from returning to a building, and the period of no food for the bat bugs becomes extended. But there have been exceptions to this as well. What about normal conditions when the bats are present? Do bat bugs also attack people and even travel down to feed on humans when bats are present in the structure? Perhaps in some cases.

But since humans are the primary host for bed bugs, and bats are one of the alternate hosts, the complement is true of the bat bugs. Thus, bat bugs tend to stay close to their primary hosts.

This was proven to me when, after more than three years of visiting the three bat-infested attics, I never once was bitten by a bat bug. In two of the three attics, I actually camped out in the attic with the bats. I slept below them during the day, and took photos at night while they flew around inside the attic. One night on my way home, I discovered (much to my dismay) I had several dozen bat bugs underneath my shirt sleeves. But none had fed on me.

ANOTHER EXAMPLE. This same scenario also is repeatedly reported in much greater frequency by the two famous bat researchers, Roger Barbour and Wayne Davis, who wrote the classic reference book "Bats of America" in 1969. They state: “Little brown bats and big brown bats (the primary house-infesting bats) are frequently preyed upon by bat bugs. In nearly every large colony in Kentucky, many thousands of these bugs can be seen crawling on the beams where the bats rest. They stay close to the bats and only rarely appear in the rooms downstairs. These insects are responsible for the popular misconception that bats carry bed bugs. Bat bugs do not molest man. In handling thousands of bats over the years, we have had many Cimex crawl off onto us, but only once has one of us been bitten.”

Well, in fact, we now know that bat bugs do bite people, but probably only when their primary hosts are either not available, or perhaps in those situations where the bat bug numbers severely outnumber their host population. It is most probable that if bats are present then bat bugs don’t readily seek out and feed on other mammals (or at least on humans). But more research is needed on host-switching behaviors among Cimicids in general, and the factors that affect this behavior.

So while it is possible to have bat bugs on the bed, and bed bugs on the bats, in most cases, if their respective primary hosts remain available, each species likely remains close to their primary hosts.

Nevertheless, whenever any Cimicid bug job is performed, the species should always be confirmed to ensure thoroughness and eliminate the possibility of callbacks due to overlooking the source of the problem. Keying out bed bugs from bat bugs is not difficult and illustrations of the two are readily available in any of the industry’s textbooks, trade magazines, or by going online and reviewing university extension leaflets.

Besides, casual generic identification of pests in the field without confirming species is indeed a questionable practice whether it is bed bugs or bat bugs, “grease ants,” “gnats,” “cockroaches,” “bran bugs” and so forth. Proper identification is the responsibility of the pest professional.

Because from time to time, there can be bat bugs on the bed and bed bugs on the bats, we must always take the time to confirm which is which.

Author’s note: For those wishing to become immersed in the technical aspects of bat bugs and bed bugs, locate a copy of R.L. Usinger’s (1966) Monograph of Cimicidae. Thomas Say Society, Vol. 7. Entomological Society of America, College Park, Md. This publication is arguably the most complete and best work on the general biology, ecology and taxonomy of bat bugs and bed bugs. It is an extremely useful reference for those specializing in Cimicid bug management programs.

The author is president of RMC Pest Management Consulting and can be reached at rcorrigan@giemedia.com or 765/939-2829.