Why Do Fleas, Ticks, and Mosquitoes Show Individual Preferences?


Why do fleas, ticks, and mosquitoes show individual preference?

Tirumalai Kamala:

Biting insects (bugs, fleas, flies, mites, mosquitoes, ticks) locate and bite their blood host targets from the chemical cues they release. Such cues are volatile organic compound (VOC) produced by their skin microbes after they metabolize human skin gland secretions, i.e., an individual's VOC profile is largely the product of their skin flora. Thus, biting preference is the outcome of how each biting insect's odorant receptors detect the VOCs unique to the individual it bites.

Skin glands include apocrine and eccrine sweat glands, and sebaceous glands (see below from 1).

Skin glands are differentially distributed across the body and human skin microbe abundance matches theirs (see below from 1).

The human odor profile consists of >400 compounds (2). Research on which ones are most important in attracting biting insects is very much in its infancy.

One small study (n = 48 adult male volunteers) on the African malaria mosquito Anopheles gambiae sensu stricto found that individuals the mosquitoes found highly attractive had different skin bacteria compared to individuals they found poorly attractive, specifically greater abundance but lower diversity of skin-associated bacteria (see below from 3).

In another small study (n = 48 adult male volunteers) Anopheles gambiae sensu stricto found individuals carrying the human leukocyte antigen gene Cw*07 more attractive (4). Since different individuals have different HLA haplotypes,

  • Each individual's unique HLA system generates different peptides, i.e., source material their skin-associated microbes metabolize and convert to VOCs is unique.
  • Each individual's unique HLA is involved in the immunological processes that culminate in their unique microbial profile since immune responses select which microbes to keep or reject.

Individual genetics also influence skin temperature and humidity profiles, and metabolic rate, which are other factors that influence individuals' differential attractiveness to biting insects. Metabolic rate influences local carbon dioxide levels, which along with ammonia and lactic acid and other aliphatic carboxylic acids influence landing rates of biting insects like mosquitoes (5).

Each human thus has a largely individual VOC profile, product of their unique genetics and unique skin microbial profile. In turn, biting insects each have their specific odorant receptors. Combinations of these two parameters likely make some humans more attractive to each such biting insect compared to others. Research on this topic is still nascent and there's more data for disease-carrying mosquitoes than for other biting insects.

Since human lifestyle, especially diet, can actively sculpt human microbiota profiles, it's likely future research will reveal how different diets could influence an individual's VOC profile and in turn increase or decrease a biting insects's preference for a particular individual.

Similar processes likely explain the differences between dogs who get ticks versus those who don't. However, in the case of ticks that's only the first step since immune status probably determines whether or not they successfully establish an infection, healthier dogs fending off ticks that could stably colonize less healthy ones.


1. Verhulst, Niels O., et al. "Chemical ecology of interactions between human skin microbiota and mosquitoes." FEMS microbiology ecology 74.1 (2010): 1-9.

2. Verhulst, Niels O., and Willem Takken. "Skin Microbiota and Attractiveness to Mosquitoes." Encyclopedia of Metagenomics. Springer US, 2015. 591-595.

3. Verhulst, Niels O., et al. "Composition of human skin microbiota affects attractiveness to malaria mosquitoes." PloS one 6.12 (2011): e28991.

4. Verhulst, Niels O., et al. "Relation between HLA genes, human skin volatiles and attractiveness of humans to malaria mosquitoes." Infection, Genetics and Evolution 18 (2013): 87-93.

5. Smallegange, Renate C., Niels O. Verhulst, and Willem Takken. "Sweaty skin: an invitation to bite?." Trends in parasitology 27.4 (2011): 143-148.

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Why Are Mugshots Made Public Before a Suspect is Convicted by the Court?

Jennifer Ellis:

Several reasons.

1. Mugshots can help find people when they have absconded, or warn people when someone is out and dangerous. So there is a good reason to share some mugshots.

2. Our legal system requires openness as per the federal constitution, and I imagine most if not all state constitutions. As such, this sort of information is not considered private and can be shared. Any effort to keep mugshots private would result in lawsuits by the press and lay people. This would be under the First and Sixth Amendments as well as the various Freedom of Information Acts. However, in 2016 a federal court ruled [PDF] that federal mugshots are no longer routinely available under the federal FOIA.

This is partially in recognition of the damage that mugshots can do online. In its opinion, the court noted that “[a] disclosed booking photo casts a long, damaging shadow over the depicted individual.” The court specifically mentions websites that put mugshots online, in its analysis. “In fact, mugshot websites collect and display booking photos from decades-old arrests: BustedMugshots and JustMugshots, to name a couple.” Some states have passed or are looking to pass laws to prevent release of mugshots prior to conviction. New Jersey is one example.

a) As the federal court recognizes, and as we all know, the reality is that if your picture in a mugshot is out there, regardless of whether you were convicted, it can have an unfortunate impact on your life. In the old days, this wasn’t too much of a problem because it really wasn’t easy to find mugshots. Now, with companies allegedly seeking to extort people into paying to get their images off the web, it has become a serious problem. Those companies may get in trouble if it can be proved that they are working in concert, getting paid to take the picture off one site and then putting it on another. But that is rare. In most cases, the picture is just public data to which there is no right of privacy under the law.

b) The underlying purpose of publicity is to avoid the government charging people and abusing the authority to do so. It was believed that the publicity would help protect people. And it does when you have a country that likes to hide what it is up to. But, it also can cause harm in a modern society like ours, where such things end up on the web and can cause permanent damage. Unfortunately, it is a bit of a catch-22. We have the right to know issues and free speech rights smack up against privacy rights and serious damage of reputation for people who have not been convicted of a crime. The law will no doubt continue to shake out over the next few years as it struggles to catch up with the technology.

This post originally appeared on Quora. Click here to view.

What Happens When You Flush an Airplane Toilet?

For millions of people, summer means an opportunity to hop on a plane and experience new and exciting sights, cultures, and food. It also means getting packed into a giant commercial aircraft and then wondering if you can make it to your next layover without submitting to the anxiety of using the onboard bathroom.

Roughly the size of an apartment pantry, these narrow facilities barely accommodate your outstretched knees; turbulence can make expelling waste a harrowing nightmare. Once you’ve successfully managed to complete the task and flush, what happens next?

Unlike our home toilets, planes can’t rely on water tanks to create passive suction to draw waste from the bowl. In addition to the expense of hauling hundreds of gallons of water, it’s impractical to leave standing water in an environment that shakes its contents like a snow globe. Originally, planes used an electronic pump system that moved waste along with a deodorizing liquid called Anotec. That method worked, but carrying the Anotec was undesirable for the same reasons as storing water: It raised fuel costs and added weight to the aircraft that could have been allocated for passengers. (Not surprisingly, airlines prefer to transport paying customers over blobs of poop.)

Beginning in the 1980s, planes used a pneumatic vacuum to suck liquids and solids down and away from the fixture. Once you hit the flush button, a valve at the bottom of the toilet opens, allowing the vacuum to siphon the contents out. (A nonstick coating similar to Teflon reduces the odds of any residue.) It travels to a storage tank near the back of the plane at high speeds, ready for ground crews to drain it once the airplane lands. The tank is then flushed out using a disinfectant.

If you’re also curious about timing your bathroom visit to avoid people waiting in line while you void, flight attendants say the best time to go is right after the captain turns off the seat belt sign and before drink service begins.

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