Thermography, or, Who Says Insects are All Cold-Blooded?

2018 September 22

As of about a week ago, I gained the ability to take thermal images [1]. This is has a lot of uses, but for our purposes it is excellent for detecting warm-blooded creatures in the dark. Oh, you know. Like the White-Lined Sphinx Moth that I posted a couple of weeks ago. It turns out that these moths were still coming around to the petunias in the evenings as of September 14, 2018. Here’s a video. The moth is the little bright orange spot that starts out a little below and to the left of center, then zooms around to the upper right before going back down to the left (I had to pan the camera around a lot to track it, and it was pretty fast, so I lost it a couple of times):

The thing is, we usually think of insects as being cold-blooded, with body temperatures very close to that of the surrounding environment. And this may well be true of insects that are sitting still. But, you know, flying is a lot of work. It generates significant heat, to the point that big moths like this sphinx moth can keep warm even when it is kind of cool out. They will cool down to environmental temperatures once they stop flying and roost, but as long as they fly, they are pretty much warm-blooded animals that can have a correspondingly active lifestyle.

And, while individual insects might have difficulty being warm-blooded full-time on their own, it gets a lot easier to keep their body temperatures consistently high when they are in a group. Like my bees! Here’s a shot of the front side of one of my hives:


The bright yellow-orange patch at the bottom is the hive entrance, and bees are flying home hot. The orange patch above the entrance is heat conducting through the wooden hive body from the cluster of bees inside, and we can see that they are clumped together near the center of the hive. Once they get inside, the bees can cluster together to maintain a constant temperature. They produce heat by vibrating their wing muscles, and can vary the compactness of their cluster to conserve heat even in subzero conditions. In fact, this is how honeybees get through the winter: the cluster maintains a constant temperature while they gradually move through the hive, eating their stored honey.

And here are a few bees around the entrance, coming and going. The S61 is actually taking two pictures, one in visible light and one in IR, and overlaying them, so we can see outlines of bees regardless of whether they are hot or not. Unfortunately, the fact that two cameras are being used means that when I get too close to the subject, the overlaid images don’t quite line up because of parallax error[2].


But, no worries. It turns out it will let me extract both a pure-thermal image, and a pure-optical image, and then I can use imageJ[3] to re-overlay and align the images, like so:


We can see that while most of these bees have a hot thorax (which is where their wing muscles are located), they are not all equally hot, and some look like they might even be room-temperature. I expect that the hot ones are the ones that just flew in, the intermediate ones are just coming out of the nice warm hive, and the cold ones are guard bees just hanging out to fend off any robber bees that might be coming in from other hives. It is interesting to note that the temperature scale on the side goes up to 36.6 deg. C, which is the temperature of the hottest bees. And this is almost exactly the same as normal human body temperature (37 deg. C).

[1] After a great deal of consideration, I went ahead and purchased a new cell phone. This is not just any phone, though. It’s a Cat S61 phone. “Cat” stands for “Caterpillar”, as in the heavy equipment manufacturer. Caterpillar doesn’t actually make these phones, but they have licensed out their trademark to Bullitt group, who specialize in producing ruggedized phones with special features. The Cat line is intended for outdoor use under dirty conditions such as what you encounter during earthmoving and mining operations. It has a lot of useful features, but the most unique one is that the S61 has an onboard FLIR thermal imaging camera. Thermal cameras are actually really useful for a lot of mechanical diagnostics, you can quickly find hot spots and coolant leaks and electrical shorts and incipient fires and all sorts of other issues that would be invisible to the naked eye. And in addition to being reasonably waterproof and shockproof, it has a complete suite of other instruments (true GPS, laser distance measurement, volatile hydrocarbons in air, humidity, temperature, pressure, magnetic fields, acceleration, a regular optical camera, you know. The works). It’s not cheap, and if all you want your phone for is general communications and social-media stuff, this is not the device for you. But if you want some serious instrumentation in your pocket, that’s another story. If we make analogies to equipment from Star Trek, it is not so much a “communicator” as a “tricorder”.

Incidentally, this phone was a huge jump for me. I still had a $9 flip-phone until a few years ago that I basically used as a pocket-watch, and my first “Smartphone” was a bare bones Samsung Galaxy Stardust that I got through Tracfone for $30. I’m not big on phone conversations, so I didn’t want to spend a lot on a phone[4] until it had a significant number of non-phone functions that actually are what I want a pocket device to do.

[2] The centers of the FLIR lens and the optical lens are just about a centimeter apart. As long as I’m at least 50 cm or so (around 20 inches) away from the subject, the camera images line up pretty well, but if I’m only maybe 10 cm away like I was for the bee pictures, the difference in which part of the subject each camera is pointing at gets significant. There is a way to adjust the alignment on-the-fly before taking the picture, but since I was trying to do it on a hand-held camera on a relatively small screen while crouching down on the grass with bees flying around my head, that didn’t actually work out all that well. It was easier to fix it in post-processing.

[3] Yes, I’m still using imageJ as my photo-editing software for this site. I’ve been using it for a long time. It has a few big advantages from my point of view: 1) It is provided for free by the National Institutes of Health (NIH), so I don’t have to buy it; 2) NIH developed and maintains it specifically for analyzing the sorts of images that you get from a microscope, and so it is better suited for insect pictures and doing the sort of image manipulations I need than more commercial software might be; and 3) It is written in Java, so I can run it on any machine that has a Java interpreter. So far, it has been able to do pretty much everything I have wanted done for the last eleven years, so I don’t see a real burning need to change.

[4] A side issue: science fiction stories and movies have been suggesting for a long time that we would eventually have powerful multifunction computers that we carried around with us to do all sorts of things. But, where the prediction fell down is that they all thought we would have a suitably impressive/descriptive/exotic name for them. Instead, here we are calling the things “phones”

3 Responses
  1. September 22, 2018

    This is fascinating! Now I’m wondering about ant hills.

  2. September 23, 2018

    This opens up so many possibilities on evening wildlife viewing!

  3. September 25, 2018

    I’m wondering about ant hills now, too. Unfortunately, the last big ant mating flight was almost a month ago, and they all seem to have already gone dormant for the winter. A scan of our driveway (where there was a lot of ant activity over the summer) didn’t show anything conclusive.

    I bet it will make it easy to find mice and squirrels at night in the winter, though.

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