Building a Garden Pond for Aquatic Insects, Part 4

pondWater, Electricity, and Avoiding Skeeters!

Now that I’ve gone over how I installed my pond at the Biosphere 2 and the things I added to it to keep the water nice and the bugs happy, I wanted to discuss a few final things: keeping my pond low-maintenance while keeping the water clean and mosquito-free.  In the interest of keeping this post within my personal word limit, I’ll finish up the pond series in my next post with some brief info about the display as a whole and the educational experience that my pond represents.

I live in a desert.  By definition, a desert is a place where there is more evaporation than precipitation, so any time you expose water to the air it tends to dry up.  Having to top the pond off every day wasn’t going to work because the Biosphere 2 doesn’t have the personnel available to do it.  Instead, I installed an automatic filling system so that the pond would refill whenever the water levels dropped so that no one will need to keep an eye on the water levels.

This was a rather simple task.  The B2 staff extended a water line from the agricultural module into the courtyard where my pond is located.  All I had to do was connect the 3/4 inch PVC pipe they left (and dug a trench for – thanks to the B2 maintenance staff for the help!  I really appreciate it!) to my pond via a simple float valve, the kind commonly used in evaporative coolers.  So, I made a trip to Home Depot and bought the supplies: a float valve, an threaded PVC connector, some PVC glue,  several brass adapters that would connect the 3/4 inch PVC connector to a 1/4 inch plastic hose (including a compression fitting), and teflon plumber’s tape.

float valve

My pond's plumbing. The float valve is the blue float in the background and you can see the hose connector on the outside of the tank.

I fitted the PVC connector onto the PVC pipe with the glue and let it sit overnight.  The next day, I wrapped all of the threads of the adapters with teflon tape and screwed them together and onto the PVC connector.  I then ran the hose up the side of the tank and connected it to the compression fitting on the float valve.  Finally, I inserted the float valve through a hole I drilled into the tank (okay, the second hole – I completely screwed up the first one, as you can see in the picture…) and turned the water on.

And got sprayed right in the face while I scrambled to turn the water back off.  After several more attempts to get the hose properly attached to the compression fitting on the float valve (let’s just say it was more than 10 attempts and leave it at that), I got everything connected and didn’t have any leaks.  I buried the pipe and the hose, piled a bunch of rocks up along the exposed part of the hose on the outside of the tank, and adjusted the float valve to fill the tank to the level I chose.  Now, every time the water level drops below that level, it opens the water valve, filling the tank automatically!

In spite of the problems I had getting the float valve and the hose connected properly, it was pretty easy to do the plumbing for the tank.  If you choose to build a pond at home, an automatic filling system seems to be an easy way to save yourself a lot of maintenance on your pond.  If you have a spigot that can be devoted to your pond, it is very easy and cheap to connect a float valve to it using the same method I used for my pond without doing any major plumbing work – you just leave out the PVC parts.  If you don’t have a spigot available, you will need to extend a pipe specifically for your pond and connect it to a float valve for automatic filling.

pump housing

The housing for my pond pump. You can't see the rock under the pump, but it's there.

The other thing the B2 staff had to do for me was extend an electrical line from the agricultural module so that I could install a pump to keep the water flowing in the pond.  You don’t have to have flowing water, but there are several reasons why you might want to.  For one, it circulates the water and causes turbulence.  This helps boost the oxygen level of the water: the more turbulence, the greater the oxygen load of the water.  I also wanted to maintain flowing water to avoid breeding mosquitoes, but more about that in a moment.

If you read my last post, you know that I stacked some cinder blocks to build a housing for my pump.  I did this so that the pump would be largely enclosed to reduce the amount of debris that might clog it.  I put a rock at the bottom of the cinder block column to keep the pump off the ground so that the silt that settled on the bottom of the pond wouldn’t get sucked into the pump and redistributed into the water.  I connected the tubing to the pump and dropped the whole thing into the housing, trimming the hose so that it extended about 10 inches above the proposed water level.  Once I filled the pond up, I stacked flat rocks over the top of the pump housing, partly to keep debris from falling into the housing, but also to provide something for the water to run over.  The tube from the pump ends just out of sight under the top rock.  This is the result:

pond waterfall

The waterfall in my pond. You can see the water flowing out of the pump's hose in the center of the image.

I think it looks rather pretty, but the mosquitoes are the main reason I though a pump was essential.  Mosquitoes are a big problem in Arizona and are attracted to water to lay their eggs.  Fortunately, there are several ways you can prevent mosquitoes.  First, mosquitoes don’t like to lay their eggs in moving water, the rationale behind the pump.  Mosquito eggs are susceptible to being washed downstream and the larvae don’t like flowing water, so female mosquitoes generally only lay eggs in still water.  My pond pumps about 300 gallons (over half of the volume of the pond) per hour.  This is enough to keep the water moving across the entire surface of the pond at all times.  Second, mosquitoes don’t like to lay their eggs in direct sunlight, as I recently learned from a mosquito biologist who works in my department.  My pond is in full sun for about 6 hours a day.  Third, you can use BT rings to kill mosquitoes in the pond as necessary, though these will also kill the other fly larvae  and potentially some of the beetles growing in the pond.  BT is the colloquial name for the toxin that the bacteria Bacillus thuringiensis produces.  This toxin readily kills a narrow range of invertebrates, including flies, butterflies and moths, some ants, bees, and wasps, and some beetles.  It has been used in powder form as an alternative to pesticides in organic farming and has been genetically engineered into the genome of several crop species (including cotton and corn) to decrease the amount of pesticides used fighting agricultural pests.  Since mosquitoes are flies, dropping BT ring pieces into the pond now and again should keep mosquitoes in check.

One final method for controlling mosquitoes involves a biological control method: mosquitofish (Gambusia affinis).  While many pond enthusiasts favor using fish in the war against mosquitoes and in spite of the fact that mosquitofish are very effective mosquito larva predators, I didn’t want to use them in my pond.  They aren’t native to Arizona and I believe they are problematic are in many of our waterways, so I am opposed to using them in case they are accidentally spread to new systems (it happens).  If I have fish in the pond, it will also drive the nitrogen levels, ammonia in particular, to levels that require control.  This involves installing a filter, which further requires swapping out filters, making sure it’s working properly, testing the water for ammonia, etc.  That is much more maintenance than my pond will receive.  So, it worked out that adding the fish I don’t like anyway wasn’t feasible with the low-maintenance requirements of my pond.  I am relying on the other three methods instead.  An added benefit of building a pond to attract insects is that it will attract several mosquito hunting insect predators as well, including giant water bugs, dragonflies, and backswimmers.  The very insects I hope to attract to my pond might control the mosquito population themselves!

Next time I’ll complete my pond series with a brief look at the educational components of my pond, including the identification guides I developed.  Seeing as educating the public about aquatic insects was the whole point of building the pond, I thought the topic deserved its own post.  I hope you’ll check back!


Posts in this series:


Unless otherwise stated, all text, images, and video are copyright © 2010

Is that a giant mosquito??!!

It’s late spring in Tuscon and we’re about to transition into summer.  This means that a lot of insects have been making an appearance in the area recently.  In particular, we’ve been invaded by one type of insect that I get questions about all the time.  It’s one I can ID without even seeing it, based solely on the description of non-entomologists.  The question is always this:

“What is that big insect with the really long legs that looks like a giant mosquito?”

The follow up question is always this:

“Does it bite?”

In case an image isn’t jumping instantly to mind the way it does for me, this is the insect that people are asking about with this question:

crane fly top view

Crane fly, top view

crane fly side view

Crane fly, side view

This insect is a crane fly (Order: Diptera, Family: Tipulidae).  That means it is NOT a mosquito (Order: Diptera, Family: Culicidae)!  Crane flies are large, slender flies with long wings and very long legs.  In the Tucson area, they are often about 3/4 inches long and with legs over an inch long, but they can get even bigger in other locations in Arizona.  These are big flies!  They also have a V-shaped line on the thorax and large large compound eyes.

I’ll admit that they do look a lot like mosquitoes, but there are several key differences.  The size is a big consideration.  Crane flies are often really big flies while most mosquitoes are, at best, medium sized flies.  Even if you’re looking at one of the smaller crane flies, one that is in the mosquito size range, there are several key differences to look for.  The mouthparts are all wrong.  Look at this photo of the crane fly, zoomed in to focus on it’s mouthparts:

Crane fly mouthparts

Crane fly mouthparts

Notice how there’s no long, needle-like mouthpart?  Mosquitoes use their proboscis to pierce the skin of their victims to suck their blood.  Crane flies, on the other hand, eat nectar or don’t eat at all.  As a result, they have thicker, blunt mouthparts with all kinds of crazy looking doodads sticking off them or no mouthparts at all.  (In answer to question 2 above, no, they don’t bite!)  And if that isn’t enough to convince you they’re not mosquitoes, take a good look at the wings.  Crane flies have smooth, membranous wings with no scales while mosquitoes usually have scales along the wing veins.

Crane fly larvae have a special place in my heart because several species have aquatic larvae, though many species live in the soil.  They’re really pretty disgusting looking, but that just makes me more fascinated with them.  Take a look at the larva in the image below and see if you can figure out why they’ve earned the common name leatherback.

Crane fly larva

Crane fly larva

Crane fly larvae have distinct heads that are often nestled down into the thorax and are hard to see (case in point: the head is on the left side of this larva).  The back ends are particularly interesting.  They have a ring of fleshy projections, often looking like tentacles, that surround the pores they use to breathe, their spiracles.  These tentacles make these really huge, fleshy larvae look extra awesome!  Unfortunately, I have never figured out what the insects use those lobes for beyond their usefulness in species identification.

I wanted to finish by mentioning one other structure that is very visible on crane flies.  Like all flies, crane flies have only 2 wings.  But did you notice those little knobby things where the hind wings would be?  If not, take a look at a zoomed-in image of them here:

Crane fly halteres

Crane fly halteres. Notice also the v shape on the thorax!

Those structures are called halteres.  Halteres are the remnants of the hind pair of wings and have been modified into new structures.  They are thought to be very important during flight, acting like a gyroscope to tell the fly how it is oriented in the air.  Crane fly halteres are very large and often highly visible due to the way the flies hold their wings out at rest – they’re an excellent fly to  illustrate these structures.  The next time you see a fly, take a close look and see if you can find the halteres!  They may be very small, but almost all flies have them.  Those tiny little wing nubs are likely why flies are such amazing fliers and responsible for their mid-air acrobatics, so they’re very important structures.

Next up is a series of posts on building a pond to attract aquatic insects, so check back in to learn all about my experiences building my pond.  Perhaps you’ll even be inspired to build your own!


Unless otherwise stated, all text, images, and video are copyright © 2010