Butt Snorkels and Breathing Tubes Oh My!
Knowing Mosquito Biology Can Help with Control
It's that time of year again, when mosquitoes start to hatch and swarm and everyone starts swatting and pulling out the cans of insect repellent. Now I know that butt snorkels doesn't sound like a true biological subject related to mosquitoes, but it really is. And knowing about them can help you control mosquito populations in your area.
Mosquitoes are a type of fly in the Culicidae family, and their name literally means "little fly" in Spanish. Many species are actually harmless, but in some, the females consume the blood of animals. It's the blood-meal eaters that are often problematic, because they are disease carriers or vectors. Their bites cause itchy bumps and are often quite irritating. That's not to say that they don't play an important biological role! They are food for many species of other invertebrates, fish, bats, birds, and more.
Mosquitoes go through complete metamorphosis with a four stage life cycle of egg, larvae, nymph, and adult. Female mosquitoes rely on fresh water to lay their eggs. This can be as deep as a pond, as shallow as a dog bowl left filled and not refreshed, an old tire, or even the inner well of a flower or plant. For those of us in the Eastern US, who are surrounded by fresh water and puddles galore, we constantly fight the standing water battle. I knew of an elderly gentleman who paid kids $.10 per tire, lid, bucket, or container to dump the standing water in them.
Most female mosquitoes lay their eggs on the surface of the water. The eggs can be in singles or in small rafts of up to 200 eggs. Some mosquito females use a technique that is similar to dragonflies, where they tap their abdomen along the surface and drop the eggs into the water. The eggs stage can last from 2 days to many months, depending on the species, season, and weather.
After about 48 hours, a young mosquito hatches into a larvae. The larvae (and pupa) are the ones with butt snorkels, or breathing tubes called siphons. The tube is an extension of their spiracles (or breathing holes along their sides -- those are used more in later life when they become terrestrial). The larval mosquito's butt snorkel has a fine ring of hairs and a waterproof material that help to break the surface tension of the water molecules. This allows the snorkel to take in air. Butt snorkels aren't all that uncommon in the aquatic insect world, some species of water scorpions and other flies have them too. Some insects like aquatic beetles attach a bubble of air to their butts when they dive, and then breathe through that. Insect butts are fascinating.
The larvae are not blood suckers yet, they are microbial feeders eating plankton, algae, and other micro materials with their brush-like mouth parts. To get away from predators they often flex their body in a jerky movement. This movement can help you identify them when you're looking in ponds or puddles.
After molting their exoskeleton about four times, the larvae then develop into a pupa. The pupa is described as comma shaped because they have a large head, fused with their thorax, to make a cephalothorax. Their abdomen is still long and skinny, and they must still use butt snorkles to come to the surface to breathe. Much like their larval stage, these pupa can use the power of their abdomen to flip around and move, so they're called tumblers. At this stage many do not have mouth parts, and they are simply hanging around with their butt snorkels in the air waiting to change into an adult. Pupation can take anywhere from 2 days to months. Here in the US many of the common species take only two weeks to complete their cycle.
After pupating, the mosquito splits its skin, and then emerges as an adult. Much like a butterfly emerging from a cocoon, the adult must harden its body and extend its wings to dry and harden, before it can fly.
If you want to control larval mosquitoes and get them before they become adults, then it's good to know about their butt snorkels and their feeding habits. First, if you can, remove all sources of standing water. This includes cleaning gutters, plant pots, refreshing bird baths, turning over tires, emptying cans, etc. Next, for water that you need standing and can't eliminate, try adding a water bubbler. The bubbling causes too much wave action for the mosquitoes to be able to use their butt snorkels and they drown, which is why you don't have many mosquito larvae in fresh running streams or waterways that move a lot.
You can also use a VERY thin layer of vegetable oil on the surface of a standing pond. This layer does not allow the mosquitoes' butt snorkels to penetrate the surface of the water. Be aware, this may affect other insects that come to the surface to breathe, or aquatic plants, so use with caution. If you do use this method, use a spray bottle with water and a few drops of oil. Gently spray the surface of the standing water until you see a thin "slick." This should evaporate in a few days, so you'll have to re-apply.
If it is feasible, one of the best methods of larvae control is using mosquito fish or tadpoles. Remember to use native species if you plan on introducing them into your body of water.
Last, but not least, you can also use bacteria. There are two species, Bacillus thuringiensis israelensis and Bacillus sphaericius, which can be added to water. These types of bacteria are eaten by the larvae and they then die from the toxins that the bacteria produce. The bacteria are suggested by the EPA and are thought to be safe and effective. You can read more on their website. My main concern with this type of control would be the effects to other native insects, so use with caution and weigh your options!
Here's a great video that you watch about their life cycle
I know that mosquitoes are a pain, but they are also biologically important. The best control you can do is prevention. If you can't prevent them, then knowing about their biology and their butt snorkel physiology can help in treating for them. Besides, now you have a cool nature fact to drag out at those summer picnics!
Stay tuned for more insect abdomen posts. Mosquitoes aren't the only ones with unique posterior appendages and uses. Female crickets have funky ovipositors (egg laying tube) and turtles can absorb oxygen and breathe through their butts! Biology is awesome.