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Preparation of skipper male genitalia in situ

     Identification of many skippers by the wing patterns is not easy. To ensure the correct determination, it is useful to examine genitalia. In males, diagnostic features are readily accessible without dissection, and pressing the abdomen of fresh specimens followed by brushing off the scales is sufficient for identification. After taking a photograph in the wild, if identification might be a problem it is useful to catch the specimen and to inspect genitalia.


All images are © Nick V. Grishin

This worn male grass skipper was photographed in TEXAS: Hardin Co., 7mi west of Kountze, 8-May-2009. Although experienced observers will recognize the species, it seemed that it might be prudent to inspect the specimen in more detail to support the determination, so the specimen was collected.


The following tools will be used: small Styrofoam block, 2 insect pins, a brush, tweezers, a magnifier (better 20x) to see what is going on and, of course, a specimen.


The specimen is pinned in a standard way.


Inspecting the abdomen from below, magnified on the right. Genitalia are hidden from view.


We are going to "squeeze" genitalia capsule out with tweezers.
Insets on all images show magnified view around the action.


Apply a gentle but firm squeeze at a point about 1/3 of the abdomen length from its end.


Release and move tweezers closer to the end. Squeeze again.


Release and move a bit more towards the end. Genital capsule should start moving out.


Finally, getting as close to the capsule as we can. Do not squeeze the hard parts of the capsule, as it will ruin it. Only soft parts of the abdomen can be pressed.


Intermediate result. The capsule is out. However, genitalia are covered with scales. Scales obscure the view. The next stage is to brush the scales off.


Grab the specimen very near the genital capsule by the soft parts of the abdomen (do not squeeze on the hard parts of genitalia!)


Hold both the pin and the tweezers with the other hand.


Prepare to brush. It is important to hold the specimen well with tweezers to prevent genital capsule from sliding back into the abdomen during brushing.


Brush well in all directions to remove scales. Unfortunately, while scales from wings are removed easily, scales from genitalia are harder to brush off.


After a few strokes we get the result: shiny genitalia with few scales.


Before (left) and after (right) brushing. The results are clear.


Sometimes a few stubborn scales are not removed with a brush. It is possible to finish them off with a pin.


Rubbing them off with gentle strokes of a pin. Working too hard may damage or tear off genitalia.


Final product, view from below, magnified on the right. A few more brush strokes may be in order to remove scales loosened by the pin.


Abdomen before (left) and after (right). Genital capsule is out and genitalia are cleaned from scales.


Final product, view from the side, magnified on the right. Several important visible parts of genitalia are labeled. The specimen can be spread as usual. Genitalia remain exserted after the specimen dries out and can be inspected later.


Side view of genitalia photographed at the highest magnification by 100 macro lens with 2x converter. Colors are a bit saturated to highlight the beauty of the structure. Now we can confidently say that the specimen is
Polites themistocles (Latreille, [1824]) – Tawny-edged Skipper




Comparison of male genitalia for the two Polites species. Specimen on the right is from TEXAS: Wise Co., LBJ National Grassland, 18-May-2009, leg. N.V.Grishin. The main difference is the shape of the lower end of valvae. In Tawny-edged Skipper (P. themistocles) it is not prominently bent, looks like a shallow boat. In Crossline Skipper (P. origenes) the lower surface is strongly bent and looks like a front of a big ship. Another easy to detect difference is on the upper side of genitalia (uncus). Uncus (plus tegumen) is more robust in Crossline Skipper (P. origenes) and is concave near the end, while uncus is rather flat in Tawny-edged Skipper (P. themistocles).



Here are the genitalia images of these two skippers from a classic book
LINDSEY, A.W.; E.L. BELL & R.C. WILLIAMS JR. 1931. The Hesperioidea of North America.
Denison University Bulletin. Journal of the Scientific Laboratories, Granville, 26 (1): 1-142.

At that time, what we call "origenes" today was called "manataagua", and the genus was "Talides".

WARNING: Image of Crossline Skipper (P. origenes) valva in James Scott book (The Butterflies of North America, A Natural History and Field Guide, Fig. 71, #495) does not seem to be a good representation of reality.


Finally, we augment a live image of Tawny-edged Skipper with an inset showing genitalia:
Polites themistocles (Latreille, [1824]) ♂ TEXAS: Hardin Co., 7mi west of Kountze, 8-May-2009


According to BAMONA database (, neither Polites species was recorded from Hardin Co. TX as of 10-May-09, thus our live photograph supplemented with the image of genitalia firmly establishes the record.


Here is the spread specimen, inset shows left lateral view of genitalia.
Polites themistocles (Latreille, [1824]) ♂D TEXAS: Hardin Co., 7mi west of Kountze, 8-May-2009


Polites themistocles (Latreille, [1824]) ♂V TEXAS: Hardin Co., 7mi west of Kountze, 8-May-2009


All images are © Nick V. Grishin



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