From grass to graphs: a fly’s journey

In my last post I talked about the workload in processing and identifying insects in the course of a big ecological project. It occurred to me that some readers may not be aware of the many steps in the process of getting a specimen from a live insect flying around a meadow to a data point in the pages of a publication. Let’s correct that oversight . . .

Here’s the short version: We collect insects in the field. And the specimen ends up on a pin, with a label. And we identify it. And then we write a paper.

Here’s what really happens . . .

1. We mostly collect using traps, which are fairly indiscriminate in what they capture. Yellow pan traps, for example, are great for collecting flies, but they also fill up with bees, ants, beetles, grasshoppers, spiders, millipedes, slugs, seeds, leaves, small rocks, twigs and much more. Time is limited in the field, so most (or all) of this gets quickly rinsed when we service the traps, goes into a small plastic whirl-pack bag and is topped up with alcohol to preserve the specimens.

Out of the trap, into the bag

2. The trap contents (or “residue”), each in its own bag (with a label on the inside!) is carefully packed for shipping back to the lab. Depending on where the samples originate, how many there are, and how they’re being transported, this can be expensive and complicated.

3. Back in the lab, each residue has to be sorted by hand to remove debris and unwanted specimens. We also change the alcohol, which by now is usually diluted and dirty. We’ll divide the specimens up by taxon at this point, with separate vials for flies, beetles, Hymenoptera, spiders and selected other things. All the remaining arthropods, minus the small rocks, leaves, twigs and slugs, go back into storage bags (we call’em sludge bags).

Leaky, smelly, and full of treasure

4. Flies in ethanol are not usually ideal for identification; most of them must be mounted on insect pins. However, mounting flies directly out of alcohol tends to produce a pretty messy and hard-to-identify specimen, so we have to process them first. Small flies move through a series of more concentrated solutions of alcohol until they’re in 100% ethanol (this removes all the water, which keeps them from shriveling as they dry). From there we move them through a couple of changes of another chemical – 1,1,1,3,3,3-hexamethyldisilazane (which, for obvious reasons, we call “HMDS”). The HMDS replaces all the ethanol in the specimen and then, when exposed to air in a fume hood, evaporates very quickly, leaving a fairly life-like, dried specimen. This whole process takes about 2-3 days for a sample, with all the soaking time factored in. Fortunately, we can process a lot of samples at the same time. Once the HMDS evaporates and the flies are dry, the samples sit in a fume hood for another few days until the HMDS smell completely dissipates. Then it’s onto mounting.

5. The stereotypical mounted insect has a pin stuck directly through the thorax. Unfortunately, mounting tiny flies this way would be like killing a vampire with a telephone pole through the heart – there wouldn’t be much thorax left. We mount each small fly on a small cardboard “point”, which must be individually punched out of a sheet of card stock, impaled on an insect pin, and run up to the correct height (yes, there are standards for this). We tend to make points a few hundred at a time. It’s delightfully mindless work for those late afternoon blocks of time when the brain shifts to stand-by.

6. Once the points are ready, each fly is individually glued to the tip of the point. All facing the same way, with a tiny drop of glue contacting the right side of the thorax just below the wing. This may seem gratuitously obsessive-compulsive (which I suppose it is) but it also makes the sorting and identification a LOT easier and faster if all the specimens face the same way on the pins, and if they have all the necessary body parts visible.

Pointed and ready for labels

7. Each sample contains a single label with the locality, date, habitat, trap type, etc – all the information necessary to extract the necessary data from the specimen once it’s identified. That single label, which isn’t always beautifully written or readable (try writing really small, on your knee, on a windy, rainy day with mosquitoes in your eyes), needs to be checked for accuracy against field notes, and then transcribed into the computer so we can make the necessary number (sometimes hundreds) of labels, one per specimen. There are also standards for label presentation that must be adhered to (someone studying those specimens in 100 years will not, probably, be able to email the collector to ask what “side hill bhnd stn, 6/7/12” actually means).

8. Every label must next be cut out (carefully!) and individual labels matched to the correct specimens, and run up the insect pin to a preset height beneath the point or specimen. And they have to face the right way. Why? Because the person who enters all the label data into the computer in a future step already has enough to do without having to twist every specimen in a different direction to read the label.

Now the specimens are, finally, ready for identification. In the next installment: from points on pins to a published paper . . .

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About terry wheeler

professor, museum director, entomologist, ecologist, naturalist
This entry was posted in In the Collection and tagged , , . Bookmark the permalink.

3 Responses to From grass to graphs: a fly’s journey

  1. Pingback: The Weekly Flypaper » Biodiversity in Focus Blog

  2. Pingback: From grass to graphs: a fly’s journey. Part 2 | Lyman Entomological Museum

  3. Pingback: How many people does it take to describe a new species? | Lyman Entomological Museum

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