This time last summer, the drought still had the rest of the year to go, and I was forced to buy water to keep the carnivores alive. This year, the rainwater reserves are loaded to the gunwales, the Sarracenia are actually growing this early in the season because of the decreased temperatures, and the Nepenthes are going mad. In my case, I can’t remember a summer quite so insane and an August so drenched since 1987. That was quite a year: that was the August where I discovered that if the rainwater in the streets rides over the axles on your bicycle wheels, you should just give up and push. That was the summer where jokes about putting pontoons on my transport really weren’t jokes, and where I spent my 21st birthday trying to get dry after biking to work through what we charitably call a “gullywasher” in Texas and the rest of the planet calls “God letting you know what He REALLY thinks about you.” It hasn’t been that bad this year, but considering that our high temperature on Tuesday was the low this time a week ago? I’m not complaining.
Because of the coolth and the surprising amount of rainfall, you may have read about our current situation with West Nile Virus, mosquitoes, and authorities in Dallas County spraying for both. Now, it would be remarkably easy to note that this was a self-inflicted issue, compounded by Highland Park and White Rock Lake residents who freak out every time they see a wayward bug. (True story: I received a call last year from a White Rock Lake gentleman who wanted to buy hundreds of Venus flytraps from me. He apparently saw a trail of ants at the end of his driveway, and wanted to build a killing hedge of flytraps around his house to eat them all. When I tried to explain that flytraps could actually attract bugs, and that they wouldn’t magically wipe out every arthropod in the timezone with intentions of coming near his house, he called me a liar. I truly wish that he was the only person with this idea, but I’ve had several others deciding that this is more “all-natural” than covering themselves with bulletproof plastic.) Instead, this started the beginnings of a Project.
Okay, to start, we’re going to need music. When dealing with evil experimentation of this sort, I highly recommend The Consortium of Genius. In fact, when it comes to projects that invoke both Doctor Who and The Red Green Show, I can’t think of anyone else.
Now, to start, consider the basic situation with the Triffid Ranch as a venue that raises carnivorous plants. Many if not most of these carnivores thrive in boggy conditions, which usually entails bodies of standing water. Standing water attracts mosquitoes, which lay eggs, which in turn become larvae. Said larvae grow to adulthood, bringing with them any number of diseases. The females collect many of these diseases when drinking blood in order to produce viable eggs, and spread them from host to host in the process. Keep the mosquitoes under control, and you control the diseases. This situation is aggravated by the fact that many of said carnivores depend upon mosquitoes as prey, and one, the purple pitcher plant Sarracenia purpurea, actually depends upon a certain number of mosquito larvae in its traps to assist with breaking down trapped prey. I need to collect lots of rainwater, preferably clean enough to use in mister systems, while at the same time making sure that it remains mosquito-free for both my health and that of everyone around me.
Now, for those with an aversion to broad-spectrum insecticides, you have plenty of options. For small applications, such as the Triffid Ranch’s Sarracenia pools, mosquito dunks work remarkably well: they contain a natural toxin derived from the bacterium Bacillus thuringiensis, and Bt is extremely effective on mosquitoes. The problem with mosquito dunks is that they’re effectively sawdust disks impregnated with Bt, and they have a tendency to break apart after a while. This isn’t a problem at all in most applications, such as with planters, old tires, or other places that regularly fill with water and then dry out. When being used in open water cisterns, though, they make a royal mess that can jam up pumps, filters, and mister systems.
Then there’s the biological controls. Traditionally, since Dallas is on a floodplain, using fish adapted to living in floodplain ponds, cattle tanks, and streams makes the most sense. The traditional introduced control is the western mosquitofish Gambusia affinis, but we also have plenty of indigenous minnows that might work. Some of them are also quite attractive, adding a benefit to using them in large rainwater tanks.
Those already familiar with using fish in rainbarrels and ponds to control mosquitoes might already be mumbling “What about goldfish, you moron?” That’s a fair question, and one that’s answered by asking you to look at last year’s heat wave in the Dallas area. Goldfish are great mosquito devourers, but they thrive best at temperatures around 68 degrees Fahrenheit (20 degrees Celsius), and we’re lucky if we see that as an air temperature during the summer. Rainbarrels and yard ponds are particularly subject to the underside of the square-cube law, where you increase the available surface area of an item as you decrease its volume. A lake will heat up in the summer much more slowly than a typical rain barrel, and during a typical July, the water in a standard 150-gallon stock tank can get point-blank hot.
It’s not just the issue with hot water denaturing brain proteins, either, although this is a concern. Anyone who stayed awake in high school biology or chemistry remembers that the higher the water temperature, the lower the amount of dissolved oxygen in that water. That’s a major factor with higher temperatures being lethal to goldfish, as they simply can’t pull enough oxygen out of the available water to survive. Many fish have options to absorb oxygen from the atmosphere in these situations: bettas and lungfish are two famous options, and anybody around a stagnant section of the Trinity River in summer (and in summer, the whole of the Trinity is stagnant) can watch both spotted and alligator gar rise to the surface to catch a quick breath of air. Mosquitofish have that ability as well, which explains their continued popularity.
Another point to consider here is that future plans at the Triffid Ranch include growing both Aldrovanda and aquatic bladderworts, both of which need very acidic, very clean water. Out here, to get that, rainwater is about the only option. Aldrovanda plants can and will catch mosquito larvae, but only bladderwort species with the largest traps could handle something as large as a larva, and most consume water fleas and other prey considerably smaller than a baby mosquito. They also need a lot of light, meaning that any tank keeping them will either have to be in full sun or exposed to a pretty impressive bank of artificial lights. They’ll need a biological control that can both handle summer water temperatures and the lower temperatures seen in spring and autumn.
Years back, a friend told me about using zebra danios (Danio rerio) in rain barrels because of their exceptional hardiness. They thrive in temperature extremes that kill most tropical fish and goldfish, and they’re particularly undiscerning about their water conditions. They breed readily, they eat like horses, and they can be brought into indoor tanks when things get cold. Since they’re most assuredly NOT going to be released into the wild at the end of a growing season, danios are already a great choice, but let’s jam the weirdness dial to “11,” shall we?
If you’ve been around a pet shop with a decent fish selection in the last five years, you’ve probably seen GloFish in one. Originally developed as a sideproject in efforts to genetically engineer a fish that glowed in response to pollutants, GloFish are gengineered zebra danios with a jellyfish gene added to its genome. Because of this, they are luminous in five colors, with the colors particularly popping in ultraviolet light. Now, that’s interesting enough for our purposes, but apparently the gene that controls the GloFish fluorescence also imparts additional temperature extreme resistance. I saw this myself about five years ago, when a malfunctioning heater in my personal aquarium left the water inside literally steaming when I woke up one morning. All but five fish died due to the temperature, and four of those were GloFish.
So, let’s recap. Heat tolerance. A firm appetite for mosquitoes. Improved opportunities for filtration and maintenance on aquatic carnivores. Designer colors. It’s too late to run a full series of experiments on their viability this summer, but I’m already making plans for next year to go along with a new 150-gallon stock tank for bladderworts. Dr. Pinkerton, could you give us an appropriate theme for the science party?