Friday, January 22, 2016

Bat mites and bat ticks...really?

Bat mite bites to humans are rare, most commonly occurring
when biologists handle infested bats or work in caves among
mite-infested colonies. Photo: Elaine Miller Bond
For me it's not uncommon to get questions about biting mites in homes. While some cases can be traced to actual infestations of rodent or bird mites, most do not. In cases where I cannot detect a valid pest, and the pest physical description or behavior doesn't reasonably match any known pest, I consider the case to likely be a non-pest problem.

However a recent email begged for help with some sort of biting bug in their home.  The bug could not be seen, the writer said, but two pest management companies suggested the problem could be either bird mites or "bat mites". According to the email, both companies treated the home with insecticide but (surprise!) the treatments did not solve the problem.

It being winter, and the client not mentioning anything about birds nesting in the home, bird mites did not seem likely. But the claim about bat mites caught me off guard.  Over the past few years I've had many callers ask about bird mites, but never bat mites. I wondered if there even was such a thing?  I could conceive of bats possibly overwintering in a chimney or attic of a home, so perhaps a winter infestation of mites is possible?  In searching my medical entomology and structural pest control books, the only reference to bat mites was Mallis' Handbook of Pest Control.

Mallis cites a single report of bat mite dermatitis published in a 1973 Journal of Medical Entomology. The report described an old rural home in northern California infested with bats. A baby in the home suffered from a chronic dermatitis on the face and abdomen.  Investigators found the child was being bathed on a sink where mites were visibly evident, next to a wall infested with Mexican free-tailed bats. Adults and an older child in the house were not bitten. Once the child's bathing site was changed, and bats eliminated from the home, the biting problem stopped. The mite species was Chiroptonyssus robustipes, whose sole host appears to be the Mexican free-tailed bat.  This was clearly an unusual situation, and one never since reported in the medical or pest control literature that I can discover. My medical entomology textbook notes that bat mites rarely bite humans, and when they do it is usually zoologists handling infested bats or otherwise working in caves among mite-infested bat colonies.

Bat ticks are not uncommon in homes where bats are active or
have recently left the structure after breeding. (Courtesy Iowa
State University)
Complicating things a bit, a colleague pointed out to me that ticks are also associated with bats. Ticks are related to mites, but larger and always parasitic. The bat tick, Carios kelleyi, is a soft tick (1/8-3/8 inch-long) and, according to an Iowa State University publication, is routinely found in bat-infested homes in that state. It is found throughout the U.S.

Ticks in the U.S. are classified as either hard ticks (family Ixodidae) or soft ticks (family Argasidae).  By far the most common human biting ticks are hard ticks, like the deer tick and brown dog tick. Soft ticks are less commonly encountered by humans and are mostly parasites of birds and bats.  They have a leathery, folded cuticle that resembles a crushed felt hat when seen from above. Carios kelleyi is of some medical concern as it has been reported to bite humans and is known to carry at least three types of pathogens, including Borrelia species, the causative agents of tick-borne relapsing fever.

I've never had a bat tick sent to me for identification, nor heard of a human bitten by a bat tick. My colleague Richard Pollack with commented that each bat tick he has received was misidentified by a professional who "should have known better". Several were PMPs, but one was a veterinarian (who thought the tick was a tapeworm segment), and a doctor who thought "it was some kind of alien being".  I hope readers of this blog will be better equipped when one of these strange critters shows up.

According to a review by Loftis et. al (2005), documented cases of bat ticks biting humans are rare with only one verified U.S. case, in Iowa--and probably the reason that the only state with an extension publication on these ticks. The solution for a bat tick infestation is removal and exclusion of the bats, along with application of residual dusts and/or sprays in suspected roosts and points of entry into the home.

Which brings me back to my email query from the worried Texas homeowner.  Given the rarity of bat mite or tick infestations throughout the country, and even greater rarity of human bites from these arachnids, its doubtful that this case was correctly identified by the PMPs involved. Because no mite or tick could be produced, it's more likely that this was not a true pest problem, and no pesticides should have been applied.  However, when called out on cases like this, it's especially important for the PMP to eliminate all possibilities, including nest parasites (mites and ticks) of birds, rodents and other mammals, including bats.

When faced with mystery bugs in a home or office situation, keep the following in mind:

  • Sticky traps can capture mites and ticks and should be used in all areas of the house where the customer believes that suspected "bites" are occurring.
  • Take the possibility of mites seriously by inspecting the structure for signs of wildlife or rodent entry. Recommend closing, or using one way doors, any suspected entry points.
  • If no evidence of wildlife is present, and no specimens of mites, ticks, fleas, bed bugs or other biting pests can be found, it's generally best to not apply pesticides.  Explain that your company follows IPM principles and that you try to avoid unnecessary applications of insecticides for the sake of your customers and the environment.

A professional knows how to deal with both the common scenarios, and understands something about the uncommon possibilities, like bat mites and bat ticks.