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What happens to your bug once you send it in to the EM laboratory?

Bug submitted with letter

The preparation of an Ugly Bug begins the moment that we receive your insect in the mail. We examine your bug with an eye for its "ugliest"/most interesting features, give it a sample number (because that is what scientists do to keep track of samples), and catalog it (so we know who sent what bug with which description). To view insects in the Scanning Electron Microscope (SEM) they must be dry, ....really dry! An electron microscope uses electrons to make images of samples, and since almost anything (even air) can stop an electron, these microscopes must have a good vacuum inside to operate. If we put a wet bug inside the SEM, we would not be able to achieve a good vacuum, and could not take pictures of that bug. So, one of the first things we have to do to prepare your insect is to make sure it is dry. How we do this depends on the insect that has been submitted. Any hard-shelled insect such as the one in the picture above can be air-dried. The chitinous exoskeleton (its hard shell) is not damaged by air drying so we can just leave it out on a table for a couple of days until it is completely dry. Other insects are not so easy. Caterpillars for example, are soft bodied and would shrivel up when air-dried. We have machines called Critical Point Driers (CPD) for these kinds of samples. These machines allow us to dry soft-bodied insects without causing them to shrivel up like they would when air-dried. To use a CPD machine we first have to soak the caterpillar or other soft bodied insect in pure alcohol (we call this 100% ethanol) to get rid of all the water inside of its body. Then we place the caterpillar inside the critical point drying machine and fill with liquid carbon dioxide (LCO2). The liquid CO2 takes the place of the alcohol inside the caterpillar. When we heat the CO2 to about 85°F the CO2 changes from a liquid to a gas. We can then release the CO2 gas from inside the critical point drier, open it up, and take out the caterpillar that is now completely dry. The caterpillar is not only dry, it still looks like a caterpillar. It is not shriveled up like it would be if we had air-dried it.

Critical Point Drier

Critical Point Drying (CPD) machine. Ours is a Tousimis Autosamdri-814 critical point drier. The sample is placed inside the chamber located below the round metal cover that is held on with three finger nuts. The black knobs on either side control the flow of LCO2 through the chamber. The gauges measure the pressure and temperature inside the chamber. The row of black buttons is for manual control of the machine.

Most of the bugs you send to us are too big to put into our Scanning Electron Microscope. There are actually many interesting parts of an insect that can be seen once you begin to look at them with a microscope. Insects have feet that are specialized for different tasks. Some have claws for grasping, others have oil covered pads for walking on vertical surfaces, and yet others have combinations of the two. Insects have specialized hairs that cover their bodies. Many of these hairs are designed to tell the insect something about its environment and are called sensory hairs. The very first thing many of you tell us you want to see on your insect is its head.

Most people imagine them to have great big eyes, busy mouth parts with strong mandibles or fangs, and waving antennae. Since so many of the bugs that are sent to us are too big to put into our SEM, we use a variation of a light microscope called a stereo or dissecting microscope to look at the bugs and remove interesting (or ugly) parts.

Stereomicroscope with dissection toolsDissecting 'Ugly Bug'

In the photos above you can see one of these stereo microscopes that we use when we "cut your bugs down to size". So... as you can see your insects do not go directly into an electron microscope once we receive them, but are first cataloged and then observed and then dissected using a stereo microscope.

Next we have to mount your insect on a holder that fits the stage inside our electron microscope. This holder can have a number of different names; "stub", "pin mount", "plug", or "specimen table" to mention a few.

Preparing stub with silver paste'Ugly Bug' mounted on stub

A piece of carbon tape that is sticky on both sides is applied to the pin mount and the insect is put on the tape with the part that you want to look at facing up. Sometimes we also use silver paste (a kind of glue with silver flakes in it) to stick your insect down (see the photo above).

To look at specimens in the SEM they must be electrically conductive. What does this mean? It means that the sample, in our case the insect that we want to look at, must be able to pass electrons or electricity through itself or over its surface. Metal objects are electrically conductive, which is why the electric company uses metal wires to send electricity to your home. To make our Ugly Bugs electrically conductive we have to coat them with a thin layer of metal and/or carbon all over their outsides.

Carbon coating in vacuum evaporator

We coat the insect with carbon first. To do this we put your bug inside a machine called a vacuum evaporator (see photo above). Once the air is pumped out we can heat a carbon rod very hot making little pieces of carbon fly off and coat the outside surface of your insect. The carbon rod in the photo above is so hot that it is almost glowing white. You can just barely see the insect on the stage, below the glowing carbon rod. Next we want to put on the metal coat and can do this with another machine. This machine is called a sputter coater and allows us to put very thin layers of "noble metals", like gold and platinum, on our samples.

Coating with gold-palladium in sputter coater

The machine pictured above is a sputter coater in action and the purple glow that you see is called a plasma. It occurs when you pump the air out of the chamber, fill it with just a little argon gas, and then pass a large amount of electricity through the argon. You can just make out the bug in the chamber surrounded by the plasma. Within the plasma, metal particles are being deposited onto the surface of the insect. Your Ugly Bug comes out of the sputter coater all shiny - looking kind of like a metal bug! Compare the before and after images below.

Bug before preparationBug after preparation