Tag Archives: diseases

Episode 184: The Mosquito!



Thanks to Kaiden who suggested we learn about mosquitoes this week! You know what eats a lot of mosquitoes? Bats! If you don’t already listen to the excellent podcast Varmints!, jump on over to it to listen to last week’s episode about bats! I cohosted with Paul and had a great time, and I know you’ll like the episode and the podcast in general. It’s family friendly and lots of fun!

Further reading:

The Paleobiologist Who Inspired the Science in ‘Jurassic Park’

SMACK SMACK SMACK SMACK:

Mosquito larvae:

An elephant mosquito in amber:

Show transcript:

Welcome to Strange Animals Podcast. I’m your host, Kate Shaw.

This week we have a great listener suggestion from Kaiden, who wants to learn about mosquitoes! This is especially great because last week I was a guest co-host on the awesome podcast Varmints!, and we talked about bats! As you may know, bats eat a LOT of mosquitoes. I’ll put a link to the Varmints! page in the show notes in case you don’t already subscribe. I think you’d like it.

The mosquito is a common insect that lives all over the world, except for Antarctica and Iceland. There are something like 3,500 species of mosquito known. In areas where it gets cold in winter some species of mosquito may hibernate, but most enter a state called diapause. This basically means that any eggs and larvae delay their development until it warms up, then develop into adults normally.

The mosquito is a type of fly, and like other flies it only has one pair of wings. Most mosquito species are only 3-6 millimeters long, gray or black in color, with long, extremely thin legs and narrow wings. The largest known species of mosquito is called the elephant mosquito, which can grow up to 18mm long. That’s almost three-quarters of an inch. Its wingspan is even larger, 24 mm, which is just shy of a full inch across.

The mosquito eats nectar. Oh, sorry, that’s the male mosquito. The female mosquito is the one who drinks blood, and she needs the blood to develop her eggs. But in fact, the female mosquito also eats nectar too, and mosquitoes even help pollinate some flowers. Some species of mosquito can develop eggs without blood, but most need the extra protein and nutrients that blood provides. In some species, the female can produce one clutch of eggs without blood, but she has to have blood to develop more eggs.

The female mosquito has a long, thin proboscis that she uses to pierce the skin of an animal and suck its blood, although the process is a lot more complicated than it sounds. The proboscis is made up of a sheath that protects the other mouthparts, including a pair of mandibles and a pair of maxillae. The mandibles and maxillae are actually the parts that cause the bite. If you look at a mosquito that has landed on your arm and is biting you, it looks like the proboscis must be stuck in your skin like a teensy hypodermic needle, but what you’re seeing is the proboscis sheath. The mosquito touches the sheath to your skin and bends it back slightly, which exposes the mouthparts and acts as a guide as the mouthparts bite you. The mandibles are the pointy ones and the maxillae have flattened ends. The mosquito moves her head slightly back and forth to lever them all into your skin, and the only reason this doesn’t hurt like crazy is because they’re so incredibly tiny, plus it happens very quickly.

Once the mouthparts have pierced the skin, the mosquito injects saliva, which contains proteins that act as an anticoagulant so the blood continues to flow without clotting. The itching and swelling associated with a mosquito bite are due to this saliva, which your body reacts to as a foreign substance, which of course it is.

This biting and saliva injecting process actually takes place very quickly, and then the mosquito sucks the blood up. She can hold up to three times her weight in blood. Not only that, but if she’s not disturbed, she will start digesting the blood quickly and will eject as much of the liquid as possible to make room for more blood, since she doesn’t need the liquid part of the blood.

Vampire bats do this too, if you’ve listened to our vampire bats episode or the new Varmints! episode about bats. They digest the blood they drink quickly, then pee out the excess liquid so they’re light enough to fly. But in the case of the mosquito, she just needs as many nutrients from the blood as possible to develop her eggs. That’s why a single mosquito may bite you numerous times. She needs to fill her stomach with the nutritious solids in the blood while excreting as much extra liquid as she can.

Once she has all the blood she needs, the mosquito will hide somewhere for a few days while her eggs develop. Then she’ll fly out to find a good place to lay them.

Mosquitoes lay their eggs in water, usually stagnant water like small ponds. The larvae stay in the water after they hatch. You may have seen mosquito larvae, since they’re distinctive. They’re only a few millimeters long and skinny, with a bristly-looking head. The larvae come to the surface to breathe through a siphon in the abdomen, so they will hang head downward just under the water’s surface. If something startles them, the larvae will curl up and sort of jerk their way through the water. Mosquito larvae eat algae and other tiny food.

Even after a larva pupates, it can still move around in the water. It doesn’t eat, but it needs to breathe, so it will hang just under the water with the breathing siphon in its abdomen at the surface, just as it did as a larva. After a few days, the pupa splits open and the adult mosquito emerges. Females fly off but the males stay in a group, and female mosquitoes join the group to find a mate.

The mosquito’s feet are adapted to allow it to stand wherever it likes. Its feet have microscopic hairy pads like those found on gecko toes that allow it to stick to smooth surfaces, and it also has microscopic hooks that help it stay in place on skin. And it also has feathery scales on its feet that are only a few microns across that allow it to stand on water. Since some species of female mosquitoes lay their eggs directly into water, being able to stand on the water’s surface is useful.

Mosquitoes spread a lot of diseases, which get injected along with the anticoagulant saliva. These include malaria, West Nile virus, zika, yellow fever, dengue fever, and many others. An estimated two million people die of mosquito-spread diseases every year, which makes the mosquito the deadliest animal in the world.

Because mosquitoes are such disease spreaders, people keep trying to figure out better ways to kill them off or at least stop them from spreading disease. One way to stop mosquitoes from spreading is to make sure there is no stagnant water around your house to breed new mosquitoes. A female mosquito will lay her eggs in even small amounts of water, such as an empty drink can that has collected rainwater, so getting rid of trash helps. In the past, people tried poisoning water or spraying insecticides, but this isn’t always very effective against mosquitoes and also kills other insects that may be beneficial.

But as genetic engineering becomes more sophisticated, scientists have discovered new ways to help stop mosquitoes from spreading disease.

For example, let’s talk briefly about dengue fever. I won’t go into symptoms or anything like that, don’t worry. It’s mostly a tropical disease found primarily in parts of Asia, Africa, and Central and South America, and it’s spread by the yellow fever mosquito, which also spreads many other diseases. People do die from dengue fever but most recover and are fine, but of course no one wants to get sick. There’s a vaccine as of 2016, but it’s not fully effective and has some side effects.

To help stop the spread of dengue fever, people have tried releasing animals into standing water that eat mosquito larvae, such as guppies native to the area. This has actually helped. In northern Vietnam, copepods that eat mosquito larvae were introduced into water storage tanks and did such a good job that the yellow fever mosquito was actually eliminated in the area for years. Some species of elephant mosquitoes, which you may remember from a few minutes ago are the largest mosquitoes in the world, don’t drink blood at all. Its larvae eat the eggs and larvae of other mosquito species, which gives it enough nutrients as an adult to lay plenty of eggs. One species of elephant mosquito specializes in eating the larvae of the yellow fever mosquito and has been introduced into some areas to help control its population.

Genetically modified male yellow fever mosquitoes have been introduced into the wild to mate with ordinary female mosquitoes in many places. The males contain a gene that causes larvae to die before reaching adulthood, and it has helped quite a bit. The yellow fever mosquito population has been reduced by over 90% in the places where the males were released, but it doesn’t affect other mosquito species that don’t carry the diseases. The problem is that genetically modified males have to be continuously bred and released in order for the program to keep working.

Very recently, as of January of 2020, scientists have engineered an antibody for the yellow fever mosquito. It basically stops the dengue virus from replicating in the mosquito, which means it can’t be passed to a human. There have been attempts to do this before, but it was only effective for one or another strain of the dengue virus. This new antibody is effective against all strains of the virus. This will help people while not killing the mosquitoes. The team is also working to engineer an antibody for other mosquito-borne viruses.

So, is it true that some people get targeted by mosquitoes more than others? As someone who seems to be a mosquito magnet when I go outside in the evening when mosquitoes are most active, I would say yes–and science agrees with me. Mosquitoes are attracted to some people more than others. The mosquito has a good sense of smell and can track animals by smelling their sweat and the carbon dioxide they exhale. They also tend to prefer people with type O blood and high body heat, but how attractive a person is to a mosquito depends on genetic traits too.

Some species of mosquito prefer some types of animals over others too. Some feed almost exclusively on birds, for instance. But in a pinch, a female mosquito will bite just about any animal, and it doesn’t even need to be warm-blooded. Mosquitoes will bite reptiles, amphibians, and even fish if they’re partly out of water. Some mosquitoes will even bite caterpillars. Caterpillars don’t have blood, but they do have hemolymph, which is just as nutritious to the mosquito.

Occasionally mosquitoes are found in amber, which as you may recall from episode 108 is fossilized tree resin. The oldest known was found in 79-million-year-old amber, so that means that yes, it could have bitten a dinosaur. But even if it still contained genetic material from dinosaur blood, and even if scientists were able to extract the dinosaur genetic material, it would be damaged DNA. Without a full genome of that particular dinosaur to compare against, we wouldn’t be able to repair the DNA sufficiently to actually clone a dinosaur. But we might be able to clone the actual mosquito and compare it to modern mosquitoes to learn more about them! It’s not as exciting as a dinosaur, but on the other hand there’s not a lot of danger of being stomped on or eaten by a mosquito.

You can find Strange Animals Podcast online at strangeanimalspodcast.blubrry.net. That’s blueberry without any E’s. If you have questions, comments, or suggestions for future episodes, email us at strangeanimalspodcast@gmail.com. If you like the podcast and want to help us out, leave us a rating and review on Apple Podcasts or just tell a friend. We also have a Patreon at patreon.com/strangeanimalspodcast if you’d like to support us that way.

Thanks for listening!

 


Episode 162: Some Seals and the END OF THE WORRRRLLLDDDD



Thanks to Kim and Pranav for their unsettling suggestions for this episode! I swear the reason I decided to do this episode this week was to celebrate getting over my cold, but then I realized I needed to address the virus everyone is talking about right now. I hope you all stay well and safe out there!

The Hawaiian monk seal OMG LOOK YOU CAN SEE ITS BELLY BUTTON, SO CUTE:

Show transcript:

Welcome to Strange Animals Podcast. I’m your host, Kate Shaw.

I’m finally over my cold, so to celebrate let’s do a little bit of an unusual episode. Last year Kim suggested we do an episode about zoonotic diseases and diseases found in polar ice, and Pranav suggested an episode about what happens after humans go extinct. Those two topics seemed to go together, muahahaha.

Zoonotic diseases are diseases that humans can catch from other animals. Rabies is a good example, since it affects all mammals and is passed from one animal to another. In fact, let’s learn a little bit about rabies since naturally people are afraid of catching it but most people don’t know much about it.

Rabies is caused by a virus, specifically the lyssavirus. It acts on the body’s central nervous system, eventually infecting the brain. After that, it infects the salivary glands in order to be transmitted to other animals through a bite wound.

When an animal is infected with rabies, it may not show symptoms for a long time—sometimes years, although it’s more usually a few days to a few months. It starts as a fever and a headache, which are also symptoms of many other diseases. But within a few days of the first symptoms, the animal becomes aggressive, attempting to bite any other animal that it encounters. It has difficulty swallowing, which is why in cartoons animals with rabies are shown foaming at the mouth. This actually happens, but it doesn’t look like shaving cream and you’re not fooling anyone. The foam is just saliva that the animal can’t swallow. In the old days, rabies was called hydrophobia, which means fear of water, because in addition to not being able to swallow, the infected animal actually shows a fear of water. This all happens because the virus wants to be transmitted to other animals, and it does so through contact with infected saliva. If an infected animal could swallow its saliva and drink water, it would be much less likely to transmit rabies. So the virus hijacks the central nervous system to make the animal afraid of water and unable to swallow.

Of course, mammals can only live a few days without water, so once an animal reaches this stage it dies within a few days. Occasionally a human who contracts rabies and starts showing symptoms is rushed to the hospital and treated, but once they’ve reached the final stages of hydrophobia, it’s extremely rare that they survive even with the best medical care available.

So that’s horrifying. Some species of mammal are resistant to rabies and while they may get sick, they don’t usually die from it, including the vampire bat and the Virginia opossum. Birds can catch rabies but usually don’t show symptoms and recover without spreading it. Rabbits and hares, and many small rodents like guinea pigs and rats, almost never catch rabies and as far as researchers know, don’t pass the disease to humans.

And, of course, a vaccine was developed as long ago as 1885, with a more effective vaccine developed in 1967. The vaccine is mostly given to dogs, cats, and other pets, but humans who work with certain wild animals, like bats, are also given the vaccine. In some areas with widespread rabies among wild animals, vaccine-laced baits left for animals to find and eat have helped limit the spread of the disease.

If you are bitten by an animal, even if the animal doesn’t show symptoms of rabies, you should get the rabies vaccine and treatment as soon as possible. Rabies is most commonly spread to humans by dogs, especially stray dogs.

Feeling nervous yet?

What about diseases that spread from animals to humans that aren’t as well-known as rabies, or which appear to be new diseases? This is what has happened with the COVID-19 virus, also called the coronavirus, that has people worried at the moment. If you’re listening to this long after it came out and have no idea what COVID-19 is, at the time of release it’s March of 2020. Also, what’s the future like? Do we have flying cars yet?

The COVID-19 virus was first reported in China and researchers think it may have originated in bats, since it’s very similar to another coronavirus found in bats. There’s also some discussion that it may have originated in pangolins, or that there may be two strains of the disease. It’s still so early in the disease’s study that we don’t know for sure, but it does appear to be a zoonotic disease.

But how would a bat virus get into a human? It’s not like rabies where infected animals are trying to bite and infect others. I mean, when’s the last time a bat sneezed on you? Well, in parts of China people still catch and eat wild animals, including bats. Most of the initial cases of COVID-19 were in people who had gone to a market where bats and other animals were for sale as meat.

Wildlife trafficking is a source of many zoonotic diseases, and it doesn’t matter whether the animal is caught to be shipped live or killed and sold as meat or body parts. Not only is it really bad for endangered species, and of course for the individual animal killed, it also puts people at risk. China has put some stricter guidelines in place to limit the practice, and hopefully other countries will do the same.

COVID-19 is a virus with flu-like symptoms, spread the same way colds and flu are spread. While most people who catch it recover after a few weeks, it can be especially dangerous for people who already have other health issues. I know you’ve been told this constantly the last few weeks, but wash your hands with soap and hot water before you eat or rub your eyes or chew on that fingernail or pick your nose. Your mouth, nose, and eyes are lined with mucus membranes, which are easy for viruses to penetrate. Regular skin is too tough for the virus to get through. That’s also why you should cover your nose and mouth when you sneeze, so no one breathes in the germy droplets you just sneezed out. Hopefully it won’t be long before a vaccine is developed, but until then, if you feel sick the best thing is to stay home and take care of yourself, and not go out and potentially get other people sick.

Right, that’s enough about your run-of-the-mill zoonotic diseases because we’re all feeling icky and nervous now. Let’s move on to diseases found in polar ice!

As you probably also know, right now the earth’s overall global temperature is rising. This is causing more ice to melt at the poles, including some of what’s called the permafrost. The permafrost is a layer of soil that remains frozen and never thaws out, or at least it doesn’t thaw completely for years—sometimes thousands and thousands of years. That kind of permafrost is mostly found near the north and south poles. But now that the earth is warming, more permafrost is starting to melt. That means everything in the permafrost is thawing out too. That includes bacteria and viruses that were frozen thousands of years ago.

Some bacteria and viruses can remain dormant in ice, then thaw out and be just fine. Researchers have found active viruses in dead bodies that are thawing after sometimes hundreds of years. The only known outbreak so far has been a case of anthrax in Siberia that spread to living reindeer from a thawed corpse of a reindeer that died some 75 years ago. The infected reindeer herd then spread the disease to some people living nearby, and one twelve-year-old boy died.

But anthrax is a well-known disease that’s still around today. What makes us all uneasy about this is that there might be unknown diseases or especially dangerous strains of known diseases that could spread to animals and people. So could that happen? Are we all DOOMED?

No, we’re not all doomed, no matter what you keep hearing on the news. Even if a virus or bacterium is fine after being thawed out, it still needs to find a host quickly or it will degrade and die anyway. The reason the anthrax virus was able to infect reindeer was because they were grazing in the area where the dead reindeer thawed out. That virus got lucky, but most don’t. The areas of the world with permafrost are ones that are difficult to live in, so there aren’t as many animals around in the first place. There are even fewer people. Instead of being worried about catching a disease from permafrost, we should probably worry about other issues stemming from climate change. If you’re like me, of course, you can manage to worry about EVERYTHING at once, but you can put polar ice diseases near the bottom of the list.

Of course, there is another aspect of melting ice and disease. In 2004 some sea otters in Alaska were diagnosed with a version of distemper that was only known from eastern North America and Europe. This population of sea otters had never been anywhere but in Alaska, so how did they catch the virus? It wasn’t until researchers noticed that outbreaks of distemper corresponded with the melting of Arctic sea ice that they realized that infected animals from other parts of the country were moving west into newly ice-free territories, spreading the virus to otters that wouldn’t have been exposed otherwise. This particular strain of distemper affects otters, seals, and other marine mammals. It’s dangerous enough that conservationists are now vaccinating Hawaiian monk seals against distemper just in case it spreads to them, since only about 1,400 Hawaiian monk seals are alive to start with.

We haven’t talked about any particular kind of animal yet this episode, so let’s learn about those seals. The Hawaiian monk seal lives around the Hawaiian islands in the Pacific Ocean, but its closest relatives, the Mediterranean monk seal and the extinct Caribbean monk seal, are both native to the Atlantic Ocean.

Hawaii, of course, is an archipelago of 137 volcanic islands, most of them quite small, that span 1,500 miles, or 2,400 km. Seven of the eight biggest islands are the ones where humans live, and many of the islands are part of a protected marine wildlife reserve. The oldest island in the archipelago is probably 28 million years old, while the youngest, which is actually called Hawai’i or just the Big Island, is only about 400,000 years old and is still volcanically active. There’s another volcanic island southeast of Hawai’i that’s still growing underwater, too.

All the islands are so far away from any continent that there are only two mammals native to the area, the Hawaiian monk seal and a species of bat. The bat probably colonized the islands after being blown there by storms, but how did seals whose ancestors were native to the Atlantic reach these islands in the middle of the Pacific? The Atlantic and Pacific Oceans are separated by two big continents on either side. Even humans didn’t settle on Hawaii until 1700 years ago at most.

Before around 3 or 4 million years ago, though, North America and South America were separate continents with a seaway between. It wasn’t until around 3 million years ago that the Isthmus of Panama formed as two tectonic plates collided, forming volcanic islands and pushing the land up. When the oceans were finally separated by this new land, it stopped marine animals from being able to pass back and forth, but of course it also allowed land animals to pass between North and South America, the Great American Interchange which we’ve talked about in previous episodes from time to time. The Hawaiian monk seal’s ancestors probably lived in the shallow seaway between North and South America, and around three million years ago one population was cut off from the rest. That population eventually migrated to the Hawaiian islands and evolved into the seals that live there today.

The Hawaiian monk seal mostly lives around the smaller islands, although sometimes it comes to the larger ones. It’s gray with a pale belly, and a big female can grow up to 8 feet long, or 2.4 meters, while males are a little smaller. Babies are born with black hair. Most of the time the seal is in the water, hunting fish, cephalopods, and crustaceans, but for about ten days out of the year it spends most of its time on land because that’s when it molts. It doesn’t just shed its hair, it also sheds the outer layer of its skin. This is probably itchy and uncomfortable until the new hair and skin grow back. The seal can hold its breath for up to 20 minutes and can dive deeply, but it usually hangs out in shallow water around the islands. It usually sleeps on the beach but sometimes in underwater caves where there’s trapped air to breathe. It also gives birth on the beach. I have to say, it sounds like it has a pretty sweet life, except the part where sharks eat it.

In the 19th century many species of seal, including the Hawaiian monk seal, were either driven extinct or nearly driven extinct by hunters. The hunters wanted the oily fat that seals produce to keep them warm in cold water, which burns really well. Fortunately, once electricity was invented and became widespread, no one wanted to burn stinky whale and seal oil for light. But many species of seal, just like many species of whale, are still having trouble recovering. The Hawaiian monk seal is so endangered that conservationists provide veterinary care when appropriate, especially to young seals that are injured by aggressive older males and by fishing equipment. And, of course, they also provide vaccines to protect the seals from diseases like distemper.

Let’s finish up with Pranav’s question. What will happen after humans go extinct?

That won’t happen for a very, very long time—hopefully millions of years, if we’re careful with our resources and wash our hands. But everything ends eventually. One day we’ll all be gone but the earth will continue without us until the sun burns out and becomes a red giant, destroying the inner planets of our solar system. That won’t be for another 5 billion years or so, so you don’t need to lie awake and worry about it happening any time soon. The earth is only about 4 ½ billion years old now so it’s probably not even halfway through its lifespan.

In the meantime, continental drift will continue to happen just as it always has. Australia will eventually crunch into eastern Asia. Africa will merge into Europe. The Americas might end up squished up with Europe and Africa again, or they might end up merging with Asia on the other side of the landmass. Either way, there will probably be another supercontinent for a while, until the tectonic plates start separating again in their constant, slow dance. Oceans will expand and contract, mountains will build up and wear down, and through it all, for thousands of millions of years, animals of all kinds will continue to evolve.

When I was a kid, I had a book called After Man by Dougal Dixon, which speculated about what animals would look like in the future. I remember being kind of disappointed that they mostly didn’t look too different from the animals we have today. Rabbits were going to do well, I remember that. But of course that’s just speculation, and we can’t possibly know what will evolve in the future. It is fun to wonder, though. Mammals have been going strong for a long time now, but that doesn’t mean they always will. Various extinction events will occur as they always have, wiping out the dominant species and opening up ecological niches for new species to evolve. It might be birds next instead of mammals. It might be reptiles again. It might be something else that hasn’t even evolved yet.

I know we all secretly want to go back in time to see what dinosaurs and other extinct animals really looked like. But we’re very lucky to be alive right now. Travel is reasonably safe, quick, and inexpensive compared to how it used to be in the olden days, so we can go to different parts of the world and see animals where they live. If we can’t travel far, we can go to zoos where animals are usually kept in habitats that mimic their natural habitats as much as possible. We can watch high-quality videos of animals in the wild. We can listen to podcasts that talk about how we’re all going to die one day, sorry about that. We even happen to live at the same time as the largest animal ever known to live, the blue whale, which always just blows my mind. We are so lucky that the blue whale is still around and wasn’t killed off for whale oil along with all those seals!

And, best of all, we know a lot more about how the world works these days. We know the mistakes we’ve made in the past, like killing whales and seals for oil, and we know how to make things better in the future for everyone, people and animals alike. So instead of worrying too much about what horrible things might happen, do your best to make the world a better place every day and wash your hands with soap and warm water. Whenever you do start to worry, just think about a blue whale swimming around in the ocean happily eating krill, or a Hawaiian monk seal lounging on a sunny Hawaiian beach. I think I need a vacation.

You can find Strange Animals Podcast online at strangeanimalspodcast.blubrry.net. That’s blueberry without any E’s. If you have questions, comments, or suggestions for future episodes, email us at strangeanimalspodcast@gmail.com. We also have a Patreon at patreon.com/strangeanimalspodcast if you’d like to support us and get twice-monthly bonus episodes for as little as one dollar a month.

Thanks for listening!