Microscopy as Tool: "Pest" Identification


Jan 1, 2021
Santo Domingo, Dominican Republic
Here in the Dominican Republic it is common that when a Dominican finds any creepy-crawly that the cry “Parasito”! is raised and then one immediately goes to seek some medication. For me, the questions are: Is it benign? Is it pathogenic? Does it create behavioral problems?

So when our “expert” found very small organisms crawling on our chickens’ feathers—I couldn’t see them at all—I decided to investigate.

I snipped the end of a feather, with the shaft, and prepared a drymount microscope slide. I examined the organism at 200x magnification and on this ~ 10x10 mm feather sample, I found about 75 specimens, most living, and some dying, probably due to the lighting and high temps. Also, along the shaft were many eggs.

Not having a camera at this time (that setup costs about $2,500.00), I began to draw. In microscopy, when you want to identify an organism, you draw over time, adding and subtracting from the drawing as you get different views.

Not having any idea as to the identity of what I was looking at this is what I came up with (my description from my drawing):

Light brown, transparent exoskeleton, in widest circumference in the middle and tapered on both ends; 1/3 distance distal from anterior end, exoskeleton dimpled in two places.

Navigates with four legs on the anterior end, dorsal side. Four trailing legs on the posterior end, ventral side.

Posterior end has 8 setae (hairlike projections) with bilateral symmetry, 4 + 4.

Size. At 200x magnification (ocular 10x and objective 20x = 200), my FOV (Field of View), as I look through my wide-angle eyepiece,
is 1.1 mm or 1,100 μm. On any axis through the center, the distance of one radius would be 550 μm or 0.55 mm. In this way, you can calculate size without a device called a reticule. I estimated that I could fit about nine end-to-end across one axis: 1,100 μm/9 = 122 μm, the length of one organism. The eggs, oblong shaped, and laid and adhered to the shaft, were about 1/3 the length of the body, so about 40 μm.

Putting a length of 122 μm in perspective (1,000 μm = 1 mm), using as example the bacterium E. coli, average length 5 μm, one of these organisms crawling on my chickens’ feathers would be the same length of 24 E. coli bacteria, end to end.

Now came time for identification. I googled “chicken parasites” and found two principal categories: mites and lice. I then went to Google Images and entered both terms. Under mites, I found a match to my drawing! The organism is the arachnid Dermatophagoides farinae. You can see from the name, that it eats dead skin. We are talking about the ubiquitous well known and hated dust mite!

So now I did a further mini-investigation. Dust mites cannot digest keratin, a principal component of skin. The skin must be decomposed via bacteria and fungi before it ready for digestion. These mites do not suck blood. They are not pathogenic and they are not vectors for pathogens, in a word, they are harmless, one exception being that some persons have an allergic reaction to the particles in the feces. So I decided against treating my chickens.

The other concern was whether I could see behavioral issues. I see none, except for scratching on the neck. Now, it could be, that the mites are an irritant and that the neck is the only area the chicken can reach with its claws . . . however, this scratching is very occasional.

I do know that chickens rid themselves of critters by taking dust baths and I have seen my chickens dig little holes, lie in them and maneuver around but this doesn’t happen often. I was thinking I could take a basin of clean sand and place that in the coop and see what happens . . .

When I get set up for photomicrography (and video) in a few months, I’ll be happy to upload some stuff. You can also see with a chicken or any bird feather how the vanes “lock” and why preening is necessary (re-lock the vanes to promote flight).


Sailing Homeward 🛸 🏴‍☠️
Premium Feather Member
Mar 29, 2021
Please upload the stuff when you're set up! That sounds so neat.

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