On my Thursday (Aug. 17, 2023) morning dog walk in Hawthorn Place I found myself engulfed by a swarm of mosquitos. I’ve experience mosquitos here before, but never quite this intense. The day before there was nothing. Then suddenly full on swarm conditions for a week. Everywhere I went on campus the bugs were intense. This past Monday my partner and I expressed deep sympathy with the little kids marshalled on the grass along Main Mall waiting for their geering up program to get started.
Mosquitos have become the topic of almost every sidewalk chat this past week. To find out what’s up I contacted some campus entomologists.
Karen Needham, Curator Spencer Entomological Collection UBC, passed me along to mosquito specialist Ben Matthews. In doing so she commented:
“I can tell you, personally, is that I was over at the UBC Experimental Ponds (not too far from your neighbourhood) last Friday and I got eaten alive! I did notice many larvae living in the large plastic tubs of standing water they have there (mozzies breed mainly in standing water), so it is not over yet. Luckily, it is only for a few weeks each year, and the larvae, pupae, and adults are an important food source for other animals, while their breeding habitats provide an additional source of water for other critters, especially in this time of drought.”
Mosquito on the hand in Hawthorn Place parklet.
I met Ben over zoom Tuesday, August 22, 2023 and we talked all things mosquitos.
A Mosquito primer
I asked Ben for a mosquito primer on the life cycle and details that would help one understand the mosquitos in our community. His response:
“We as humans have been coexisting with mosquitoes for a very long time. There are about 3500 different species around. There are a handful that are of biomedical importance because they transmit parasites and viruses like malaria and dengue and yellow fever, west Nile and all of those. So a lot of what we know is based on very few species.”
“In general, mosquitoes have aquatic larval and pupal stage. They spend about a week, sometimes two weeks, as aquatic swimming larvae and pupae, and then they emerge directly on the surface of the water as flying terrestrial adults.”
“Most mosquitoes, but not all, will blood feed, and it's only the females that blood feed, so the males do not. It's because it's not for nutrition per se. It's for reproduction. The protein that comes in the blood meal is broken down by the adult female, and then she'll convert that into eggs that she's developing in her ovaries. The reason that they're so good at transmitting disease is that they go through these cycles, so they'll bite, they'll take the blood, they have to digest it for about three or four days, and then they lay their eggs, and then they'll go back and bite again.”
“The way that a mosquito transmits disease is that she has to bite a human or an animal that is infected with a virus or a parasite. Then she becomes infected. Then she can transmit on the next cycle, the next time that she bites.”
“That's why the handful of species that we kind of worry the most about, from a medical point of view, are the ones that really have evolved to prefer human beings over all other animals. So we call them anthropophilic. You can put them in the middle of a zoo, and they will take the humans walking around rather than the other animals. In a pinch, they might feed on other animals, but they have developed a very strong preference for, in particular, the smell of humans. They can detect humans from a distance. They're very sensitive. Their sense of smell is primarily through the antenna, and they just pick up on compounds that are put off by bacteria that live on our skin (this is the current thinking).”
“There are some species of mosquitoes that don't blood feed, and instead what they do is their larvae are predatory and gather all of the nutrition and all the protein that they will need for the adults to then go on and develop eggs.”
I asked Ben how long might mosquito eggs lie dormant in the ground.
“It depends on the species,” Ben said. “But they can last for years, in some cases, until the environmental conditions on the ground are ripe for them to hatch and to emerge. So that's one of the adaptations that we actually study in a mosquito that evolved in sub Saharan Africa, Aedes aegypti, which is a yellow fever mosquito. There we know that it's their adaptation to get around the dry season. There are many months of the year where there's no water similar to our summer here. What they do is they lay the eggs, and then the eggs go into a dormant state where they just can sit and wait until they're submerged in water. Depending on the species, it can be anywhere from months to years.”
“We'll see that with the snowmelt mosquitoes in particular in BC, if they get a dry spring, they'll just wait until the next one, and then if they get a wet spring, then they'll emerge.”
Next I wondered how long the adults live.
“Depends on whether somebody swats them or not,” Ben said. “But it can be several months, it can be two to three months. So that's why one mosquito can potentially become infected with something and then bite maybe a dozen other people in the course of its life. A lot of what we know about their lifespan comes from the lab, and there's certainly a lot of mortality as time goes on. But it is not unusual to think about a single female mosquito being alive for months. When they're not feeding on blood, both the males and the females tend to feed on nectar. There's actually some good evidence from a former postdoc in my lab, Dan Peach, who studied this when he was a PhD student at Simon Fraser (supervised by Gerhard Gries), that they're actually effective pollinators as well. So just like bees, the male and female mosquitoes will feed on nectar from flowers, and they can pick up pollen as they do that. Then as they move on to the next flower, they can actually serve as pollinators.”
What gives with all the mosquitos?
I asked Ben to help explain what’s up with all the mosquitos this year. I noted that over the years I’ve lived on campus I’d never experienced this swarming effect. In the past there would be mosquitos through the summer, but last week it was like someone turned on a switch and boom, out came the bugs.
“I suspect it's different,” Ben said, “in that everything has been concentrated this year. If I can ask you to remember if you were in town two weeks ago, pretty much to the day, that was the last time we've had rain. Before that we had no rain for, I think, six weeks. So the only rain we've had in about two months time was that one concentrated period about two weeks ago. What mosquitoes do, many of them, is they lay their eggs near a body of water, but not directly in the body of water. And the thought process for them is that the larval and pupal development -the immature stages- are fully aquatic. They need to exist in water for about a week, ten days, two weeks, depends on the species, depends on the environment. The adult female will lay her eggs near water because that's a body of water, but then they'll wait until it rains, and then the eggs will be submerged and then they'll hatch.”
“What I suspect walking around our neighbourhood, I live down in Westbrook Village near the softball field. I suspect what happened is basically two weeks ago, all of the eggs that had been laid in the spring and the summer hatched all at once. What we're now seeing is about two weeks out from that event, all of the adults are around, and now the weather is hot and dry, or warm and dry at least, and that's kind of perfect adult weather. So we're just noticing them. I suspect that we're probably not dealing with more mosquitoes than we would in a normal summer, but just that instead of them being spaced out, they just emerged all at once. We went from zero to 100 in the span of about a week.”
“What might be the effect of climate change?” I asked. “Might that have an impact on the concentration of the mosquitos?”
“Absolutely,” Ben said. “We see this with other species of mosquito in other places of BC and the world with snowmelt. So there are a lot of species of mosquitoes that will hatch when the snowmelt comes. If you have a relatively large snowmelt, you'll get a certain emergence pattern. If you don't have a lot, then you might get fewer. It's not quite as simple as saying it will always result in more or fewer, but I think you're right. I think it probably reflects at least this summer we had a very unusual precipitation pattern. The fact that we had that one day of rain meant that it synchronized everything. If I had to guess, if we had no rain, we probably still would have no mosquitoes just because it's been so dry for so long. The normal process of having standing water, sitting around because of rain and all of that, that wouldn't have been supported in the same way it would in a normal season. That's my suspicion of what's going on in our part of the neighborhood.”
I noted that “I grew up in north coastal British Columbia, and the mosquitoes I experienced growing up, I've always found them a lot more aggressive and pervasive than the ones down here. I always used to think of these ones as a little lackadaisical. They kind of stumble around in the air. They're a little bit easier to swat out of the air. So I was doubly surprised when I had found my body covered in dozens of mosquitoes in no time. The blood dripping down the legs.”
“I don't know what species of mosquitoes these are around here at the moment,” said Ben. “There are certainly different host preferences and different levels of aggressiveness across different species. It could be that it's a particularly good year for a human preferring species, and so we're seeing the effects of that. Or it could just be, again, that the numbers are around because I had the same experience. If you stop for even just a few minutes when you're walking or biking, if you're wearing shorts, you look down and there are dozens of mosquitoes. It is true that there are different levels of aggressiveness, different levels of flight capability and all of that, but the ones that we have right now are particularly annoying. I would agree with you on that.”
Ben’s Lab
Before ending our conversation I asked Ben to tell me a bit about the work being done in his lab.
“We mostly study Aedes aegypti, which is the yellow fever mosquito,” Ben said. “But we've also grown really interested in a coastal rock pool mosquito, Aedes togoi, which you can find on the BC coast. We have a field site in Lighthouse Park in West Van. We're really interested in their sensory systems; their sense of taste and smell and also mechanosensation. So their touch, sense of touch, basically, and how they use this to find victims to bite and choose whether or not to feed, but then also specifically how they select egg laying sites. This is a question that I've become really interested in, is the mother gets one shot at this.”
“There's no parental care in the traditional sense of sticking around and actively caring for your offspring. Her parental care is in choosing the best place to lay an egg so that it has the best chance of hatching and surviving once it's become submerged. So there are a lot of really complex decisions about how much salt is in the water. Are there chemicals associated with predators? How deep is the water? How soft is a substrate? Can she embed an egg so that it will stay and not fall off too early and get predated upon? We're interested in how they make decisions and how they navigate the world using their sensory systems.”
“We use genetics to get at this and behaviour and neuroscience techniques, kind of treating them like a model organism, the same way a fruit fly or a mouse has been used in the past. But these are animals that you can't really model using a fruit fly, for example, because they [fruit flies] don't blood feed and they don't lay eggs near water. So we're taking advantage of all of the new kind of developments in genetics and neuroscience that have happened over the last ten or twenty years to really focus in on mosquitoes directly.”
Parting words
As a wrap I asked Ben to share a fun fact by which to end our chat with.
“I think I like to go back to the biodiversity of mosquitoes we know and are annoyed by,” Ben said, “the handful of species that find and bite us and transmit disease. But some of my favourite mosquitoes are ones that, for example, feed on amphibians. They've specialized on very particular things that aren't humans, and they just exist in the environment and do their thing.”
“I guess mosquitos get a bad rap for a good reason. I don't want to encourage people to learn to love mosquitoes per se, but just to realize that there's more to them than just the nuisance that they are in the summer. [For now] it's long pants and insect repellents for us.”
Thank you for the timely article!
Thanks for the excellent explanation. I've been wondering what's up with the mozzies; they're even biting me, and they usually prefer other humans. In my culture we say some people have "il sangue amaro," bitter blood, and mosquitos don't like the taste, but I think that's a folk belief.