Viewing Eyelash Mites

In this lab exercise, mites in the genus Demodex will be used as an example of organisms in class Arachnida.
Note that you will need QuickTime to view the movies.

Background Information on Class Arachnida:

The crayfish Web page provides an introduction to Phylum Arthropoda, in general, and gives characteristics of the main subphyla and classes within that phylum. That page/lab also focused more specifically on Subphylum Crustacea. In this lab, we will be focusing on Class Arachnida within Subphylum Chelicerata, and in the next lab, we will focus on Class Hexapoda within Subphylum Atelocerata.

Arachnid orders include the following. There are others; this is only a partial list of the most “common” ones around here. To confuse matters further, some authorities consider these groups to be subclasses with other orders within them, while other taxonomists consider these to be orders. For now, we’ll say they are orders.

• Order Scorpiones or Scorpionida, the scorpions, which have a poison sting at the tip of their abdomen, just above their anus
• Order Araneae or Araneida (aranea, aranei = spider), the spiders, which have the chelicerae modified as fangs with poison glands (used to paralyze prey), have spinnerets on the abdomen from which they produce silk for their webs, and are beneficial predators
• Order Opiliones or Phalangida (phalang = finger, toe), the daddy-long-legs and harvestmen, which have long, slender legs, are not spiders, and do not spin webs
• Order Acari or Acarida, the mites and ticks, many, but not all, of which are parasitic — some are aquatic, with both marine and fresh-water species, some live in detritus (leaf litter) and are scavengers or predators, and others live and feed on plants

Thus, eyelash mites are classified as:

Kingdom Animalia
         Phylum Arthropoda
                  Subphylum Chelicerata
                           Class Arachnida
                                    Order Acari
                                             Family Demodicidae
                                                      Genus Demodex
                                                               Species folliculorum and brevis

To give you a better idea of “who’s related to whom,” if Acari is considered to be a subclass, then Order Trombidiformes (trombid = a little, timid one) is inserted under that (if Acari is considered to be an order, then Trombidiformes would be a suborder). Interestingly, Trombidiformes is the same order/suborder in which chiggers are placed, although they are in a different family within that order/suborder.

Background Information on Interspecies Interactions:

Interspecific interactions (inter = between, among) are interactions between/among organisms of different species. Any/every time organisms of different species are interacting with each other, it is considered to be some type of an interspecific interaction. Typically, these interactions are classified based on whether they are beneficial to one or both of the species involved or whether they are detrimental to one of the species involved.

Symbiosis is used to describe any relationship that involves two (or more) species living together and interacting. This is a general term which includes predation, parasitism, commensalism, mutualism, etc., but often is used, somewhat incorrectly, to mean mutualism.

Commensalism is the term used for a relationship between two species that is beneficial to one but of neutral benefit to the other. Cattle egrets follow cattle to feed on the insects stirred up by the grazing cattle. This benefits the egrets (they get food), but neither benefits nor harms the cattle.

Mutualism is used to describe a relationship between two species where both benefit. The yucca moth both pollinates and feeds on the yucca plant; acacia ants live in the thorns of, defend, and are fed by the acacia tree in which they live; and trees, in general, can’t get along without mycorrhizae living in/on their roots and absorbing food for them. Many plants and their pollinators have evolved mutualistic relationships.

The relationship between eyelash mites and humans is typically one that would be called “commensalism.” The mites benefit from a place to live and lots of free food, while normally, the “benefit” to humans is of neutral value.

Background Information on Eyelash Mites:

As mentioned above, eyelash mites are in genus Demodex (demo = people, fat; dex = an insect, a worm). There are two species that live on humans.

These microscopic mites (Demodex folliculorum and D. brevis) live in the sebaceous glands in the hair follicles not only around the eyelashes, but also on people’s noses, cheeks, foreheads, etc. One source claimed that both adults and immatures pierce epithelial cells to eat the cytoplasm, but other sources say that they feed on dead skin cells, body oils, and other “leftovers” that accumulate in the hair follicles. Whereas the slightly-larger females tend to stay in “their” hair follicle (head in, posterior end poking out), males come out, usually at night, to move around on the surface of the skin to look for mates.

D. folliculorum measures 0.3 to 0.4 mm in length, whereas D. brevis is about half that size (0.15 [= 150 μ m] to 0.2 mm) with a similar head and thorax but a shorter abdomen. That’s amazing because these are complex, multicellular arthropods, yet are only slightly larger than a single-celled Paramecium! Like other Arachnids, they have eight legs, and it has been estimated that they can move at a rate of 8 to 16 mm/hr. Their bodies are long and somewhat scaly to help anchor them in the hair follicles. Their mouthparts (tiny chelicerae and pedipalps) resemble those of spiders, scorpions, and other arachnids, but are much smaller and designed for eating skin cells and oils within the hair follicles. Mites, like all their other arthropod relatives, have a tube-within-a-tube body plan. These mites live in the follicles, oriented parallel to the hair shaft, head inward, often with the tip of the abdomen (the opisthosoma — opisth = behind, the hind part) protruding. A single follicle may contain as many as 25 D. folliculorum mites.

It has been estimated that their life cycle, from egg to adult, takes about 14.5 days, including about 5 days as an adult, and it has been reported that females may live an additional 5 days after oviposition. Interestingly, sexual maturity is reached in the larval form (called neoteny). Females remain within “their” hair follicles while (at night) the males wander over the skin’s surface from follicle to follicle in search of females. Copulation occurs at the opening of the hair follicle, after which the female crawls back into the follicle near the opening of the pilosebaceous gland (oil gland associated with a hair follicle — pilos = hairy; sebum = grease, tallow) to lay her eggs.

The mites are transferred between people through facial contact (a mother kissing her baby), and it has been estimated that 96 to 98% of all people harbor these mites. In most cases, people don’t even know they have these mites, but rarely (perhaps due to a suppressed immune system) the mite population can increase enough to cause skin problems, resulting in a condition known as demodicosis. A different species of Demodex causes mange in dogs.

Bibliography

anon. Demodex mite: Information from Answers.com.
http://www.answers.com/topic/demodex-mite (22-IX-2005)

anon. How do I do the test (Information for the Dermatologist or yourself). Demodex Solutions reveals the facts about demodex mites.
http://www.demodexsolutions.com/default.asp?faq.asp~mainFrame (22-IX-2005)

anon. 2001. Mystery Organism Quiz Answer - August00. BioMEDIA ASSOCIATES.
http://ebiomedia.com/feat/ansOct00.html (22-IX-2005)

Bell, Russell. 2000. The Diversity of Life.
http://www.alumni.caltech.edu/~rbell/DiversityOfLife.html (22-IX-2005)

Roque, Manolette R. and C Stephen Foster. 2005. Demodicosis. eMedicine.com, Inc.
http://www.emedicine.com/oph/topic517.htm
http://www.emedicine.com/oph/byname/demodicosis.htm (22-IX-2005)

Procedure:

In this lab you will be making a “wet mount” of material you collect from your face, but you will be using salad oil rather than water as the medium in which you will be placing your specimen. Due to the fact that these mites inhabit the oily environment in people’s pores, the use of salad oil on your slide will be a closer approximation of their natural habitat.

Some sources say that, “It is quite easy to look for your own Demodex mites, by carefully removing an eyelash or eyebrow hair and placing it under a microscope,” but in years of looking for them via that method, I have never had any success at finding them that way. However, you are certainly welcome to try that method. Using the method explained below, I have never had any trouble finding mites, often several on one slide.

Note: one Web page quotes a procedure, similar to the following, as explained on page 177 of

Wilson, Edward O. 1992. The Diversity of Life. W. W. Norton. New York.

Several other Web pages quote the same procedure, but neglect to reference E. O. Wilson’s book as the source of that quote, while several other Web page authors use other slight variations on this method.

Obtaining samples from different face parts (forehead, nose, cheeks) may boost your chances of finding mites.

1. Place a drop of salad oil onto a microscope slide as though you were going to make a wet mount. Optionally, separate drops could be used for different samples from nose, cheek, etc., but it would probably be easier to just make one sample of everything mixed together.
2. Use the fingers of one hand to stretch the skin of the area to be sampled. Using a long fingernail, the edge of a second microscope slide held at a 45° angle, or the side of a knife or spatula blade (I’ve found that fingernails work just fine, so skip the sharp stuff), press down hard enough to squeeze some sebum out (hold your fingernail at an angle so it works more like a scraper) and scrape the tool sideways across the skin to collect a “gob” of the mixed sebum, discarded skin cells, etc. Note: do not pull a knife or glass slide across the skin as though cutting! You don’t want to cut yourself, just squeeze sebum out of your hair follicles. Rather, use a sideways motion, like shaving with a razor or scraping ice off the car windows.
3. Use a toothpick to remove the obtained sebum from the scraping tool (as in, the gunk that has collected under your fingernail), put it into the drop of oil, and gently mix it so the sebum will dissolve in the oil. Samples from different areas of your face may optionally be placed into separate drops of oil or may be combined in the same drop. As the sebum dissolves in the oil, this will help to free any mites that are present, making them easier to see.
4. Place the coverslip on the slide. You may gently move the coverslip from side to side and/or gently tap on it with the eraser end of a pencil or the wooden, handle-end of a teasing needle to help spread out the sample. This will help to free the mites from any debris in which they might be “hiding” and make them easier to see.
5. Examine the slide under the microscope. Scan the drop at 40× looking for mites. When you find one, you may increase the magnification to see more details (keep in mind, if you don’t see anything at 40×, they won’t suddenly appear by magic if you switch to 100×). As the microscope light warms the slide, that will increase the chances that you may see a mite moving, so between that and the fact that the sebum may still be dissolving in the salad oil, if you don’t initially see any mites, don’t give up too soon — be patient and keep looking. One Web site reports that, “They can live away from the host approximately 36-58 hours in a drop of oil.” The immature mites don’t crawl around like the adults do, but it is reported that at higher magnification, you can occasionally see their mouthparts moving.
6. Draw pictures of any mites that you see, label the body parts that are visible, and take notes on any movement that you observe. Note how many mites you see. If you put samples from different areas of your face into different oil drops, note how many mites you found in each location.

Mite Anatomy:

Eyelash Mite
Labeled Eyelash Mite Find these body parts on your mite and label them in your illustration.

• As is typical of all members of Subphylum Chelicerata, mites have two body parts: cephalothorax and abdomen. The cephalothorax is often called the prosoma (pro = before, in front of; soma = body), and the abdomen is often called the opisthosoma (opisth = behind, the hind part). The prosoma is comprised of the gnathosoma (the portion that bears the chelicerae and pedipalps, gnatho = the jaw) and the podosoma (the portion that bears the legs, podo = foot). Note that these regions do not neatly correspond to “head” and “thorax” — the eyes, if present, typically occur on the top of the podosoma. In many other species of mites, even the visible distinction between cephalothorax and abdomen (prosoma and opisthosoma) is vague or lacking.
• As is also characteristic of all chelicerates, mites, at least as adults, have eight walking legs. Acarids in general have a life cycle in which a newly-hatched mite larva only has three pairs of legs. When it molts to a nymph, it gains its fourth pair of legs. There is usually at least one more nymphal instar (the actual animal between molts — the first instar occurs between hatching and the first molt), before the mite molts to an adult. Again, keep in mind that these are multicellular arthropods with jointed, multiple-segmented legs. You will probably see your mite’s legs moving.
• As is typical of all chelicerates, mites’ mouthparts consist of anteriorly-located chelicerae (cheli = a claw, hoof), which resemble small pincers, and outside (laterally)/behind of (posteriorly to) them, the pedipalps (pedi = a foot, palp = touch, feel). (Note that, in the spiders, the chelicerae are modified as fangs, and in the scorpions, the pedipalps are modified as large pincers: they have “chelicerate pedipalps.”) Often, you will be able to see your mite’s chelicerae moving in and out as they search for food to ingest.

Other Eyelash Mite Photos:

Cephalothorax at Bottom Left, Legs to Right (© DBF)

Abdomen at Top (Note Segments) (© DBF)

Close-up of Abdomen

Close-up of Abdomen

Close-up of Cephalothorax, Mouthparts to Right

Close-up of Cephalothorax, Mouthparts to Right

Close-up of Cephalothorax, Mouthparts to Right

Close-up of Cephalothorax, Mouthparts to Right

Quicktime movies

• Movie 1 (2.25 MB Quicktime)
• Movie 2 (2.58 MB Quicktime)

Other Things to Include in Your Notebook

Make sure you have all of the following in your lab notebook:

• all handout pages (in separate protocol book)
• all notes you take as you read through the Web page and/or during the introductory mini-lecture
• all notes and data you gather as you perform the lab
• labeled drawing(s) (yours!) of any mites that you were able to see
• answers to all discussion questions, a summary/conclusion in your own words, and any suggestions you may have
• any returned, graded pop quiz