• Choose a category
• All
• Classic-Fiction

By Root 843 0

usually once a patient feels better. Few people, in fact, seem to realize the danger posed when they decide to stop their antibiotic treatment before it’s complete—and here’s why. Think of a hypothetical population of 1,000 microbes inside a person who has been instructed to take an antibiotic for seven days. Discounting bacterial reproduction for a moment (since this is a model), let’s say the antibiotic kills 900 microbes by day five and 990 by day six. If the patient were then to stop taking the antibiotic after day six, which microbes would be left alive? The ten survivors who were the most resistant to the antibiotic in the first place. Now factor in bacterial reproduction—and as these surviving microbes begin to multiply, each new generation will have the same antibiotic resistance exhibited by the ten original survivors.*118

Now that we’ve seen some of the nasty effects of chiggers it’s time to figure out just what they are. The short answer is that they’re the parasitic juvenile stages of some mite species.†119

And what about ticks?

Like chiggers, their story has become an extremely important one because of the pathogens they transmit through their bites. Starting in the mid-1970s, there has been growing concern in the United States and elsewhere over tick-transmitted diseases—especially Lyme disease and Rocky Mountain spotted fever.

Are ticks (like bed bugs) a pest on the rise, and if so, why? Are tick-transmitted pathogens also becoming immune to our treatments, or is there another answer? And what about Lyme disease? Why are the symptoms so variable (ranging from minor annoyance to catastrophic and life altering)? Some people believe that there’s a chronic version of the disease—one that the experts refuse to talk about. And while we’re in conspiracy mode, whatever happened to Lymerix, the Lyme disease vaccine?

All right, before we deal with the grassy knoll (and the chiggers lying in wait there), let’s cover some basics. First of all, chiggers, mites, and ticks are not insects, but like insects, they belong to the enormous invertebrate phylum Arthropoda. In fact, they’re members of the only arthropod group that rivals the insects in diversity—Arachnida (a subphylum that also includes the spiders and scorpions).

While chiggers aren’t exactly blood feeders, they merit interest because their blood-sucking cousins, ticks, share much of their biology as well as their penchant for strange behavior. Additionally, hundreds of mite species are vampires as adults. It’s just that many of them feed on nonvertebrate blood—like hemolymph, the blood found in arthropods like insects. Some of these mite/insect interactions have also been in the news lately, especially as they relate to agriculture and the honey bee industry.

Evolutionarily, mites and ticks are extremely close. In all likelihood, tick ancestors (prototicks) were actually mites that somehow evolved to become obligate blood feeders (similar to vampire bat ancestors, which were non–blood feeders).

Why did some mites retain their larval blood-feeding lifestyles into adulthood while other body characteristics (like sexual organs) developed normally? The answer is that maintaining larval (or juvenile) characteristics as an otherwise mature adult is yet another example of how new species can evolve. The basic premise, proposed by the evolutionary embryologist Gavin de Beer (1930) and reinvigorated by Stephen Jay Gould in his book Ontogeny and Phylogeny (1977), is that “evolution occurs when ontogeny*120 is altered in one of two ways: when new characters are introduced at any stage of development with varying effects on the subsequent stages, or when characters already present undergo changes in developmental timing.”

In the first scenario, Gould’s “introduced characters” result from genetic alterations like mutations—changes in an individual’s genetic blueprint that occur during DNA replication.*121 It is at this time that errors (variations to some) in the copying mechanism result in mutated strands of DNA. In this classic explanation of how evolution