Wrigglers, tumblers and skeeters

It’s that time of year – the time when any foray out to the country or conservation area necessitates packing a can of deet-filled bug spray, when bug jackets and bug traps and bug lights and bug incense all start flying off the shelves. When many people lose many hours of sleep listening to a whine in the corner of the room. When a new dance move, more widespread and familiar than the twist or macarena, begins to be seen at outdoor gatherings. When the mosquito starts to fly.

Mosquitoes are ubiquitous and cosmopolitan, occuring on every continent except for Antarctica. We tend to think of the insects as simply “the mosquito”, but in fact there are 3000 species around the world. Most of these occur in the tropics, however North America has somewhere between 150 and 170 described species north of Mexico. In Canada, where the climate is, for the most part, much harsher and habitats less varied than through the US, that number is just over 70 species, and in Ontario it’s somewhere around 50. But still. Fifty species of mosquitoes just in my home province. Identifying the various species usually requires an expert and a microscope. The Roger Tory Peterson of mosquitoes, Richard F. Darsie Jr., has dedicated most of his career to learning and studying them all and their life stages, and is still going strong at age 90. He lives in Florida, still frequents the University of Florida’s entomology department, and continues to update his 380+-page identification and range guide to North American mosquitoes. I sure hope I’m that active and together when I’m that age!

For the rest of us, the 150 species all just get lumped into the same broad category of “the mosquito”. Mosquitoes are members of the order Diptera, which contains the flies. Like all flies, mosquitoes have just one pair of wings, a pair of vestigal wings called halteres, used for stabilizing the insect in flight, and a pair of relatively large compound eyes. Unlike most flies, mosquitoes have a specialized mouthpart, a tubed proboscis that they insert into the skin of their target to suck out blood. The proboscis is not a smooth tube, as one might expect, but is serrated, which minimizes the points of contact that the proboscis has with the host’s tissue. Unlike a smooth needle which most people can feel being (painfully) inserted, the tiny serrations ensure that very few, if any, nerves are contacted while the mosquito is feeding, and it’s possible for the host to never feel the bite or know the mosquito is there. Of course, it’s not foolproof, and often the proboscis will hit a nerve on the way in – resulting in a quick reflex that the mosquito may or may not survive.

Only female mosquitoes take blood. Mosquitoes don’t actually need blood to survive – males will never ingest any, and a female could live out its whole life without ever having a “blood meal”. Adult mosquitoes actually feed on nectar, like most flies. An adult can live for 2-3 weeks, or as much as 6 months, depending on the species. The longer-lived species are generally ones that overwinter as an adult rather than as an egg, and can sometimes be found buzzing around your house in the dead of winter when there’s a warm spell.

The blood is necessary for the development of eggs, as the female needs the protein available in the blood to produce them. Female mosquitoes generally find their targets at a distance of tens of metres/yards by detecting exhaled carbon dioxide and various body secretions such as sweat, and hone in once they get closer through sensing infrared heat given off by the target’s body. Some people will attract more mosquitoes than other people based on these things (for instance, men, because they’re generally warmer and sweatier, are likely to attract more bugs than women). Mosquito repellents work not by poisoning the mosquitoes or creating a distasteful barrier, but rather by disorienting the mosquito’s infrared honing system. Because of this repellents are not 100% effective, as the insect can still by chance, luck, or a missed area, land on and bite its target, but they’re pretty good.

Because they are blood-suckers, and inject saliva into their targets, mosquitoes are problematic vectors of many diseases. These primarily occur in the tropics, but some, such as West Nile which was introduced to North America in 1999, have made it into temperate areas. Mosquitoes are estimated to transmit diseases to 700 million people around the world annually, many of which are fatal. The mosquito-borne parasite malaria causes the death of 5.3 million people, mostly young children, every year.

The reaction to mosquito bites varies by individual. The very first bite any person gets will not swell or itch, but antibodies are created from that bite that result in subsequent reactions. The itchy bumps are essentially an allergic reaction by your body to the mosquito’s saliva, which contains more than 15 different proteins, including one to prevent clotting, one to disable platelets, one to dilate blood vessels, and others that aid in sugar digestion and nectar feeding. With continued bites some people can become desensitized to the saliva, while others can become hyper-sensitized, with mosquito bites causing severe allergic reactions with rashes, blisters and bruising.

The specific saliva composition varies from species to species, so immunity to one species does not necessarily guarantee immunity to another. My mom recounts that us girls could go outside and play for hours when we were younger and hardly be bothered by the mosquitoes or show any reactions, but when we went on a camping trip a few hours away we all found the mosquitoes horrendous – presumably a different species that we had no immunity to. These days I find I react to the mosquitoes around my parents’, but they don’t bother me too much and providing I don’t scratch them the bumps don’t itch and subside within an hour or two.

A mosquito has four life stages. Females will lay eggs on the surface of water. For this they need still bodies of water – eggs laid on a river’s surface would just get swept away. Any body of still water will do, regardless of size, and standing water in birdbaths, old pots or tires, eavestroughs, etc, can be a breeding ground for baby mosquitoes. Public awareness programs advocate dumping standing water and clearing your eavestroughs to eliminate potential breeding locations, and providing that you don’t live near a pond or a lot of puddles, it will probably work. This is more practical in town, however, where mosquitoes aren’t as much of a problem to begin with. Out in the country the accepted approach to dealing with mosquitoes is just that – just deal with them. There are many products that advertise repellents or control, but they’re hard to avoid altogether.

The above life stage, the larvae, are known in many places as “wrigglers” or “wigglers” for their habit of moving through the water by rapidly whipping their tail end back and forth. When they’re not moving, they tend to sink into the water with their tail tip at the surface and their head pointed downward. Most species of mosquito have a tube, called a spiracle, on the tip of their tail which they poke out of the water and use for breathing. One method of large-scale mosquito control involves laying a substance over the surface of the water that blocks the larvae from breathing.

Mosquito larvae eat micro-organisms and organic matter in the water, and are themselves food for many other creatures, including fish, amphibians, reptiles and other invertebrates. The latter includes the larvae of other mosquito species, specifically those in the genus Toxorhynchites which are sometimes known as “mosquito hawks” (this genus also happens to be one of the few where the females do not take blood). They have been used in some areas as a natural form of mosquito control, but are found in tropical and subtropical forests, so aren’t an option for most of North America.

A couple weeks ago my mom and I started noticing these round, dark invertebrates in the water in my parents’ water garden. We had no idea what they were, but they seemed to have just suddenly appeared. We brought one in and looked at it under the microscope, where it appeared to have a giant thorax with a couple of short antennae, and a long abdomen that folded underneath it. It wasn’t shown in my mom’s aquatic invertebrate guide, and we were stumped, so my mom sent the photo off to an invert expert at the University of Guelph.

It turned out to be the pupal form of the mosquito. Known by many as “tumblers” for their somersaulting movement through the water. The pupal form of many invertebrates is often stationary, but mosquitoes are very active. The two little antennae on its head are its breathing spiracles. The pupal form has no mouth, so its movement through the water is primarily a predator avoidance response, or to move to better conditions (such as out of the sun).

When I went back with my camera I found this empty pupal case stuck to the water hyacinth, just above the water line. Nearby were two newly-emerged adult mosquitoes, resting quietly on the water hyacinth bulb, waiting to dry out. Another reason that mosquitoes need still water is this emergence process – in areas with large expanses of open water it’s not possible to affix to vegetation or rocks, and the mosquito emerges at the water surface, where it rests until its wings and body are dried out and hardened and it can then fly off.

Adult mosquitoes are not strong fliers, and a slight breeze (or a fan) is enough to keep the bugs from bothering you. They fly at about 1-2 km/h (0.62-1.24 mph), for up to 4 hours at a time, and on a still night can fly as much as 10km (6.2 mi). I presume this is not usually actually in a straight line, but rather is the distance covered if the mosquito’s looping movements were unwound into a straight line (like measuring a long-distance runner’s laps of an oval track), but it wasn’t actually stated. Mosquitoes are mostly crepuscular or nocturnal, but they can be very active in the deep shade of the woods, as well. Or just about anywhere, for that matter. But they tend to avoid direct sunlight. In the day they’re usually found resting on vegetation, and walking through long grass in the shade of a forest edge can often throw up clouds of the insects.

The whine associated with mosquitoes is produced by the high-frequency whirring of their wings. This high-pitched noise isn’t heard by many adults, but is heard by nearly all younger people. As I was browsing the net for info, I discovered that this concept has been applied to a product called a “mosquito alarm” – not actually anything to do with mosquitoes at all except in its similar sound frequency. Rather, it’s a high-pitched noise that most adults can’t hear, but most young folks can, and is placed in areas where teens tend to gather and socialize, which can be very offputting for adults, especially if they have to wade through the groups to a store entrance or such. Many towns and stores in western Canada have started installing these and claim to have a great success rate in that they no longer have loiterers in the areas where the “alarms” have been installed. Teens can take it the other way with a “mosquito ringtone” for their cell phones, a high-pitched tone that just the younger folk can hear, allowing them to receive messages in class, or other forums where they aren’t supposed to have or use their phone.

I have several other things I could mention, but I think I’ll stop there today. I’m sure knowing all this won’t make you any happier to be out in the swarms, but at least you’ll have something to tell your friends as you’re swatting!