Where we examine the various summer insects that are out to drink our blood
by Joe D. Shorthouse MANITOULIN—Insects are the most abundant animals on Manitoulin Island. There are more species of insects here than all other species of animals combined, and our natural ecosystems would collapse without them. Most Manitoulin insect species go unnoticed as they spend their lives providing ecosystem services such as breaking down organic matter, eating other insects, or pollinating plants. However, some species cause us endless grief because they feed on our blood. These insects, and a few other species of small animals that also feed on blood, are the subject of this two-part series. In Part 1, mosquitoes, black flies, horse flies, and deer flies are discussed. Centuries ago, everyone fed on the blood of deer, elk, snowshoe hares, and birds, but once humans arrived, we quickly expanded their banquet options. In Part II, lice, fleas, bed bugs, and ticks are discussed. Ticks are not insects, but since they are related arthropods and are of concern to the residents of Manitoulin Island, they are included. Although most of us cringe at the thought of animals eating our blood, a few hours at the exhibition provided a new perspective on the role blood feeders play in our environment and the surprising ways they adapt to their lifestyles . For the animals discussed in these two articles, blood is an energy- and nutrient-rich food source used to produce eggs. However, a problem for all vertebrate blood feeders is that blood easily clogs the tiny mouthparts. To prevent this, blood feeders have developed anticoagulants in their saliva. Although anticoagulants solve a problem for blood feeders, it is saliva that accounts for much of our discomfort when we feed, and in many cases, it is saliva that transmits disease. There are two types of blood feeders—so-called capillary feeders and pool feeders. Capillary feeders such as mosquitoes, bedbugs, lice and ticks have mouthparts modified to form two flexible tubes in which they seek a blood meal from a vein beneath the surface of the skin. In one tube they inject anticoagulants to stop the blood clotting, while in the other they suck the blood meal. They can usually feed without alerting the host to their presence. Pool feeders such as horse flies, deer flies and black flies cut a hole in the skin and wait for blood to flow freely and pool. They add anticoagulants to the droplet and surround the blood pooling on the surface. The bite of most pool feeders is painful. Mosquitoes Adult mosquitoes are the flying insects most disliked by humans. They buzz in our ears as we try to sleep and their bites cause itchiness, welts and swelling. There are about 82 species of mosquitoes in Canada and 67 in Ontario and probably about 50 species on Manitoulin Island. The appearance of the adults of each species is scattered in the season and so there are mosquitoes to bother us throughout the warm months. Although delicate little flies, mosquitoes are the deadliest animal to humans on the planet because of the infectious diseases they transmit. Mosquitoes kill hundreds of thousands more people in the world each year than all other deadly animals combined. Mosquitoes are both aquatic and terrestrial. However, they spend most of their lives in the aquatic stage. Eggs are laid in stagnant water and hatch into mobile larvae called wrigglers that feed on algae and microscopic debris floating in the water. Larvae cannot breathe underwater and must come to the surface where they use a breathing tube on their dorsal surface to get oxygen. The larval stage lasts from six days to two weeks depending on the species and water temperature. Unlike most other insects, the larval stage of mosquitoes actively swims, but does not eat. It has a comma-shaped body and also has to come to the surface to get oxygen. Although mosquitoes are sensitive, they can fly long distances and have an uncanny ability to locate human hosts. Adults are about 6-8mm long, with long, massy legs. Their heads have large eyes and a pair of long antennae. The antennae of males are bushier than those of females and contain auditory receptors to detect the characteristic whine of the female’s wings. Mosquito wings beat 300 to 600 times per second. Their large eyes allow them to see people several meters away and the sensill on their antennae to detect levels of CO2 and other compounds that are expelled as we breathe. They can detect sweat and other body odors, along with body heat, and as a result, some people are more attractive than others. Mosquitoes can smell body odor and CO2 up to 20 meters away. Adult mosquitoes can feed at any time of the day, depending on the species. Most species feed actively at dusk or dawn. Both females and males feed on nectar which they use for energy. However, only females feed on blood used to produce eggs. Most mosquitoes feed on warm-blooded mammals or birds. Mosquitoes that feed on birds transmit West Nile virus. Development from egg to adult takes about 40 days. Adults live one to two weeks. Most mosquitoes rest in a cool place during the heat of the day and wait until the evenings before foraging for a meal, although they may still bite if disturbed. Mosquitoes are some of the most adaptable and successful insects on Earth, and they are found in some unlikely places. Virtually any natural or man-made collection of water can support mosquito larvae. Mosquitoes have been discovered in mines nearly a kilometer below the surface and on mountaintops at 420 meters. Mosquitoes easily fly through the open windows of vehicles and houses and look for people to feed on. Black flies Black flies are robust small flies (most are 5-8 mm long), black or gray that are a scourge on humans and livestock across Canada. They are most common starting around mid-May and can continue to make us miserable until June or even July. They can bite at any time during the day, but do not feed at night. Unlike mosquitoes, they are insensitive and look more like a small prairie buffalo, hence their other common name “buffalo gnats”. Black flies have a habit of swarming and are most annoying when they get under our clothes and feed on our blood without being noticed. They do not transmit disease to humans, although their bites are painful, itchy and slow to heal. Some people have an allergic reaction to their bites. Black flies have short legs and antennae. There are 162 species in Canada and about 63 in Ontario and at least 40 on Manitoulin Island. Like mosquitoes, they are both aquatic and terrestrial, with most of their lives spent as larvae in fresh flowing waters of streams and rivers. They have one generation a year. Their eggs are laid on the edges of streams and rivers in mid-summer. When the larvae hatch, they sink to the bottom where they attach to rocks using hooks on the back end. Larvae are shaped like small urns and bend in the direction of the current with their heads down. Their mouthparts consist of folding fans that expand when feeding to catch passing debris such as organic particles, algae and bacteria. The larvae took food into her mouth every few seconds. Larvae develop into pupae, an inactive stage of development in which they do not feed. The nymphs develop into adults that float to the surface in an air bubble. Adults are ready to fly when they emerge from the water and immediately seek a blood meal. They can lay eggs immediately after a blood meal. The average lifespan of an adult black fly is three weeks. Mature adults can disperse tens or hundreds of kilometers from their breeding grounds under their own power or with the help of prevailing winds, complicating control efforts. Both males and females depend on plant nectar for their flight energy, while females require blood for egg development. Males are rarely seen and do not feed on blood. Females have specialized mouths with serrated “stilettos” that they use to slice through the skin to expose blood vessels. Anticoagulants in saliva also partially numb the feeding site, reducing the host’s awareness of being bitten and thereby extending the flies’ feeding time. Blood continues to collect at their feeding sites after the flies have left. Feeding often causes local swelling and inflammation and the site itches. Heavy feeding can cause “black fly fever,” probably caused by the anticoagulant, resulting in headache, nausea, fever, swollen lymph nodes, and joint pain. Black flies only feed during the day and tend to zero in on areas with thinner skin such as the neck or ears and ankles. Interestingly, they will not feed on people inside vehicles or houses. Manitoulin Island black flies do not transmit disease. Horse flies and deer flies Horse flies and deer flies are large, robust flies with prominent compound eyes. As their names suggest, their main food sources are the blood of large animals such as horses and deer. However, they will feed on any large mammal they can find such as cows, dogs and humans. Deer flies will readily seek human blood, while horse flies feed less often on humans. Both flies are often found buzzing around stables and fields. Depending on the species, we may be bothered by horseflies and stagflies from May to September. There are approximately 3,700 species of horseflies in the world with 144 found in Canada. There are about 44 species of deer found in Canada, most likely on Manitoulin Island. Horse flies and deer flies can be…
