In defense of ultraviolet

By now, a fair number of carnivorous plant enthusiasts know about the new paper on fluorescence of Nepenthes, Sarracenia, and Dionea traps under ultraviolet light. First and foremost, for all of you undergrad and postgrad students out there, take this as a warning not to procrastinate in finishing and submitting a scientific paper. I was about maybe a month away from submitting my own paper to the Carnivorous Plant Newsletter on the subject, and not only did the authors of this paper beat me to the punch, but they produced an exceptional paper that presented distinctive blue fluorescence spots that nobody else had caught before now. They did exceptional work, they deserve every last bit of publicity they’re receiving, and I just regret not having the proper gear for proper research.

That said, there’s a lot more to be done with fluorescence in carnivorous plants. I can state with authority that many other genera of carnivore fluoresce under UV, including at least two species of Heliamphora,Darlingtonia, and the two carnivorous bromeliads Catopsis and Brocchinia. In fact, Catopsis fluoresces brightly enough to hurt. There are other advantages to running around your carnivorous plant nursery with UV lights, but I’m getting ahead of myself.

The whole strange experiment with carnivores and UV started about five years back. Peter D’Amato of California Carnivores noted about three years ago how brightly some species of Sarracenia, particularly S. leucophylla, seemed to stand out under moonlight, and I noticed that myself when looking over Sarracenia propagation pools during a full moon. Likewise, after damage from sudden hailstorms, I took a good look at the trap contents of those particularly bright Sarracenia and noticed that a majority of the prey items consisted of moths. The moths didn’t have any particular interest in visible light color variations, and many would have no interest whatsoever in the nectar secreted along the rims and lids of the traps. So what attracted them?

Since I was the sort of kid who cracked most Encyclopedia Brown mysteries by the third-to-last page and who went digging to verify the plausibility or lack thereof of Danny Dunn novels, it wasn’t hard to recognize that the moths were seeing something that I couldn’t without assistance. The initial research was easy, but I’m again getting ahead of myself. The problem involved getting photos that verified observations. Almost anyone who studied any level of high-school botany or natural history remembers photos of flowers taken “with a UV filter” that allows UV-blind humans to see the patterns on seemingly boring flowers that draw in bees and sawflies. Just try to get a breakdown on how to do this, though, especially in the digital camera age. Half of the advice I received was completely worthless (hacking your camera to detect infrared does nothing, and just wasted my time), or it was tantalizingly vague as to how those photographers managed to pull it off. I even hired my adopted daughter Jenny to take photos of Nepenthes and Sarracenia while using a UV filter, but the results were inconclusive at best. That’s one of the reasons why I’m so impressed with the photos taken by the Plant Biology authors: they bypassed all of that by using low-light photography and controlling the exact wavelength of UV used.

In further developments, I’m still publishing, but only after quite a bit of revision. Among other things, it’s time to note the number of other carnivores that show similar fluorescence, and the variations therein. For instance, Darlingtonia, the cobra plant, fluoresces along its trap aperture, but it also has veins of fluorescence along the ala, or wing, that runs up the shaft of the trap, presumably to encourage insects up the ala to the aperture. Venus flytraps fluoresce, with varying patterns with different cultivars. Oh, and the greatest fluorescence among sundews is at the tips of its trapping hairs, with the dew at the tips absolutely shining under UV.

Now, there’s no reason why you can’t experiment with this as well. In fact, after running a few tests, I hope to present a regular shortwave and longwave UV display at plant shows comparable to fluorescent mineral displays in rock shows. This sort of equipment isn’t absolutely necessary, though, and most experiments in carnivore fluorescence can be done with a simple UV light.

Black light fluorescent fixture

To begin, don’t bother with standard “black light” fixtures, either fluorescent or incandescent. Not only do these put out relatively little UV, but they emit so much visible light that the plant fluorescence is nearly unnoticeable. These will still work with one exception, to be related later, but for most investigation, save the money for a better option. About the only fluorescence you’ll get off a carnivore with one of these comes from dying leaves, and if you can’t spot that under visible light, this won’t help.

UV LED flashlight

That better option is a good UV LED light, preferably a battery-powered one that can be used in the field. These days, with the drop in prices in UV-emitting LEDs, it’s possible to find plenty of good LED flashlights at affordable costs, with and without standard white LEDs for double duty. I picked up mine from American Science & Surplus for two reasons: it has six UV LEDs surrounded by white LEDs so I can use it as a standard flashlight, and the switch glows in the dark. You may laugh, but drop one of these in the dark, and that improves the odds of finding it.

Sonic screwdriver - closed

And then there’s the one I use for plant shows with lots of kids, because they completely lose it when I pull it out and turn it on. This, of course, is my scorpion detector, as it’s just as good at causing scorpions to fluoresce as carnivores. It has one good, powerful UV LED in the tip, which already makes it very handy for shows, and it has a pen attachment at the other end for leaving notes on business cards and stickers. The best thing about it, though?

Sonic screwdriver - open

It extends. Particularly when showing the bright patches at the back of the throat of a Nepenthes pitcher, that’s a lot less intrusive than manhandling a pitcher into place for a larger light source. It won’t work well in bright light, but it gets the job done.

Now, instructions for using LED lights. If at all possible, try to use your new lights in as dark a set of conditions as you can get. When working outside, try for a new moon and a minimum of street and porch lights for the best effect. Indoors, go for the darkest room you can get and let your eyes adjust to the darkness before lighting everything. Contrary to news reports on how these “glow in the dark”, the effect is going to be a bit subtle, much like using UV lights on a piece of opal. With proper precautions, though, the effect is not only obvious, but one of the LED flashlights mentioned above can detect carnivores from as much as three meters away. Go for a longwave UV lamp, such as those used for diamond prospecting, and have some real fun.

And for a last word, there’s one additional benefit in wandering through your carnivorous plant collection with a UV flashlight. My dear friend Ryan Kitko recently wrote about the bladderwort, Utricularia bisquamata, that was infesting his shield sundew. U. biquamata has quite the reputation as an aggressive pest in carnivore collections, but I have a soft spot for it. Firstly, it’s very easy to care for, and it makes an excellent starter plant for those who want to work with bladderworts but who don’t have the facilities to raise any of the true aquatic species. Give U. bisquamata soggy soil and lots of light in a standard terrarium, and it takes over, producing lots of white-pink slipper-like blooms with a pastel yellow spot on the top.

The other reason why I’m so fond of U. bisquamata? Get outside with a UV flashlight and find out for yourself. That yellow spot may be pastel under visible light, but under UV, it fluoresces like a black light poster. Considering how many birds are able to see into varying frequencies of UV, I now understand why both the migratory ruby-throat hummingbirds and their competing rufous hummingbirds won’t stay out of my greenhouse. I’ve had hummingbirds literally tapping on my office window to get at U. bisquamata and U. sandersonii blooms, and now I know exactly why.


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