How Invasive Crayfish Help More Mosquitoes Thrive

iStock
iStock

When invasive species somehow find their way into an environment where they don’t belong, they can disrupt everything from the food web to public health.

Recently, researchers at UCLA and other California institutions discovered an unwelcome squatter that might directly affect the spread of mosquito-borne disease. It’s the red swamp crayfish, a tasty delicacy often found in gumbo that may also be allowing mosquito populations to thrive.

Native to the southeastern U.S., the crayfish are now found in California. While investigating their damaging ecological presence, scientists made a chilling observation: In streams where crayfish concentrations were high, there was a noticeable spike in the number of mosquito larvae. They found something else, too—a sharp decline in the larvae-eating dragonfly nymphs that they would expect to see in the area.

In the paper, published in Conservation Biology, lead author Gary Bucciarelli observed 13 streams in the Santa Monica Mountains. Eight had crayfish populations and were high in mosquito larvae but low on dragonfly nymphs. Five crayfish-free streams had more nymphs and fewer larvae.

In a lab experiment putting the crayfish, mosquitoes, and dragonflies in proximity, Bucciarelli watched as the dragonfly nymphs—normally happy to prey on mosquito larvae—kept their distance in the presence of crayfish, apparently spooked by the crustaceans. In the wild, high concentrations of crayfish appear to be interrupting the dragonflies' hunting habits, allowing more mosquitoes to roam unchecked.

That’s not great news for humans. Mosquitoes are notorious for spreading viral diseases like West Nile, Zika, and malaria. In Los Angeles, where the mosquito population could conceivably get a boost, 15 of the 16 mosquito species can harbor pathogens that pose a threat to public health.

No one is quite sure how crayfish spread to the area—it’s possible fishermen used them as bait decades ago—but it's likely their presence will continue interfering with native species. In 2015, a nonprofit backed by the California Department of Fish and Wildlife started removing crayfish from the Santa Monica streams using traps set by volunteers. The captured crayfish were sent to Malibu to become snack fodder for opossums and raccoons. But it’s a sizable task. Roughly 600 crayfish might be caught in a given day out of the millions thought to inhabit the waters.

Conservationists might soon pursue more aggressive means to combat the crayfish's damaging ecological footprint. In addition to scaring dragonflies into inaction, they can threaten the integrity of underwater dams by burrowing and consume plants that help purify the water.

h/t National Geographic]

Why Does Humidity Make Us Feel Hotter?

Tomwang112/iStock via Getty Images
Tomwang112/iStock via Getty Images

With temperatures spiking around the country, we thought it might be a good time to answer some questions about the heat index—and why humidity makes us feel hotter.

Why does humidity make us feel hotter?

To answer that question, we need to talk about getting sweaty.

As you probably remember from your high school biology class, one of the ways our bodies cool themselves is by sweating. The sweat then evaporates from our skin, and it carries heat away from the body as it leaves.

Humidity throws a wrench in that system of evaporative cooling, though. As relative humidity increases, the evaporation of sweat from our skin slows down. Instead, the sweat just drips off of us, which leaves us with all of the stinkiness and none of the cooling effect. Thus, when the humidity spikes, our bodies effectively lose a key tool that could normally be used to cool us down.

What's relative about relative humidity?

We all know that humidity refers to the amount of water contained in the air. However, as the air’s temperature changes, so does the amount of water the air can hold. (Air can hold more water vapor as the temperature heats up.) Relative humidity compares the actual humidity to the maximum amount of water vapor the air can hold at any given temperature.

Whose idea was the heat index?

While the notion of humidity making days feel warmer is painfully apparent to anyone who has ever been outside on a soupy day, our current system owes a big debt to Robert G. Steadman, an academic textile researcher. In a 1979 research paper called, “An Assessment of Sultriness, Parts I and II,” Steadman laid out the basic factors that would affect how hot a person felt under a given set of conditions, and meteorologists soon used his work to derive a simplified formula for calculating heat index.

The formula is long and cumbersome, but luckily it can be transformed into easy-to-read charts. Today your local meteorologist just needs to know the air temperature and the relative humidity, and the chart will tell him or her the rest.

Is the heat index calculation the same for everyone?

Not quite, but it’s close. Steadman’s original research was founded on the idea of a “typical” person who was outdoors under a very precise set of conditions. Specifically, Steadman’s everyman was 5’7” tall, weighed 147 pounds, wore long pants and a short-sleeved shirt, and was walking at just over three miles per hour into a slight breeze in the shade. Any deviations from these conditions will affect how the heat/humidity combo feels to a certain person.

What difference does being in the shade make?

Quite a big one. All of the National Weather Service’s charts for calculating the heat index make the reasonable assumption that folks will look for shade when it’s oppressively hot and muggy out. Direct sunlight can add up to 15 degrees to the calculated heat index.

How does wind affect how dangerous the heat is?

Normally, when we think of wind on a hot day, we think of a nice, cooling breeze. That’s the normal state of affairs, but when the weather is really, really hot—think high-90s hot—a dry wind actually heats us up. When it’s that hot out, wind actually draws sweat away from our bodies before it can evaporate to help cool us down. Thanks to this effect, what might have been a cool breeze acts more like a convection oven.

When should I start worrying about high heat index readings?

The National Weather Service has a handy four-tiered system to tell you how dire the heat situation is. At the most severe level, when the heat index is over 130, that's classified as "Extreme Danger" and the risk of heat stroke is highly likely with continued exposure. Things get less scary as you move down the ladder, but even on "Danger" days, when the heat index ranges from 105 to 130, you probably don’t want to be outside. According to the service, that’s when prolonged exposure and/or physical activity make sunstroke, heat cramps, and heat exhaustion likely, while heat stroke is possible.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

This article has been updated for 2019.

Two Eco-Minded Kids in England Are Petitioning McDonald’s and Burger King to Nix Plastic Toys

romrodinka/iStock via Getty Images
romrodinka/iStock via Getty Images

Some kids are not content to wait around while the grown-ups sort out the future of our planet. Two of them, 9-year-old Ella and 7-year-old Caitlin, have launched a petition on Change.org requesting that McDonald’s and Burger King stop giving out plastic toys with their kid’s meals, Thrillist reports.

“Children only play with the plastic toys they give us for a few minutes before they get thrown away and harm animals and pollute the sea,” the British girls wrote on Change.org. “We want anything they give us to be sustainable so we can protect the planet for us and for future generations.” The petition has almost 400,000 signatures so far, and their current goal is to reach 500,000.

McDonald's Happy Meal
McDonald's

Last October, UK environment minister Thérèse Coffey also implored McDonald’s to stop giving out plastic toys, suggesting instead that they develop smartphone-friendly games to accompany the meals. At the time, a UK McDonald’s spokesman acknowledged the importance of reducing plastic waste and cited their promise to switch to paper straws, but countered the assumption that the plastic toys were only used for a few minutes, telling The Telegraph that they “provide many more fun-filled hours at home, too.”

The fast food giant did study the environmental effects of their toys last year and found that they are hard to recycle, since they’re manufactured from various types of plastic. As a result, McDonald’s is researching more Earth-friendly ways to make their toys. A Burger King representative told The Wall Street Journal that it, too, is exploring “alternative toy solutions.”

But according to Ella and Caitlin, “It’s not enough to make recyclable plastic toys—big, rich companies shouldn’t be making toys out of plastic at all.” The young activists themselves recycle as much as they can, and even hung a poster in their window about saving the planet.

You can sign their petition here, and learn how to reduce your own environmental impact.

[h/t Thrillist]

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