Author Archives: meh9

Invasive, Sex-Crazed Cannibals

The popular perception of ladybugs. Clipart by Marketa Bauerova.

I was studying outside the other day when I began to notice a couple of small, alligator-like insects circling the outer rim of my table. Curious about these little creatures, I let one crawl onto my hand. It looped around my fingers for a while with surprising speed until I placed it back down and it continued its little circuit around my table.

Using the internet’s infinite wisdom (this website in particular), I was able to identify the insect as a ladybug* larva. In particular, it was an Asian Multicolored Lady Beetle, or Harmonia axyridis. The first things that I discovered about my new friend is that it emits a pungent odor and sometimes bites. I looked down again at the bumpy insect squirming around my table with a newfound sense of disgust, hoping it hadn’t left it’s odorous mark on me.

And that was just strike one for this ladybug.

I was talking to a friend a little while later when our conversation was cut short by the sudden appearance of a larvae falling out of my hair. My voluminous hair has been known to consume anything from bubble gum to bobby pins, but this was certainly a first. Even later, I found one squished in between the pages of a textbook. I knew that I was either very unsanitary, as my friend now suspected, or that they were so common that all of these interactions were not improbable. In any case, I knew that there would be some interesting science behind my insect encounters.

An Asian multicolored lady beetle larva found by the fountains near Brochstein Pavilion (on Rice University Campus). Photo by Marie Hoeger.

Asian Multicolored Lady Beetles in North America

It turns out that the Asian Multicolored Lady Beetle is an introduced invasive species that is causing some trouble in North American and European countries. They have been released multiple times in North America as biological control agents (they’re very effective aphid predators) from as early as 1916. They failed to establish in North America until 1988, when their populations started exploding. Now, they are expanding at an extremely rapid rate — approximately 442 km per year (read a chapter from this book to learn more about the impact and history of Asian Multicolored Lady Beetles in North America).

These lady beetles have been shown to be highly successful in controlling aphid pest species, as intended. An adult eats roughly 60 aphids per day, and even smaller larvae eat around 25 aphids per day. However, the benefits to humans only last through summer and spring. Around fall, they migrate in masses and become a common pest. They flock to houses and other man-made structure as winter approaches to hibernate in cracks and crevices. Their massive aggregations stain carpets, curtains, furniture, and more.

Because they’re such highly generalized and effective predators, they’re also harmful to many native and non-target species. On top of depleting the food source, they actually eat the eggs of their native brethren (this type of predation is called intraguild predation — it’s literally a ladybug eat ladybug world they live in). Although native species’ larvae also prey on Asian lady beetle eggs (not so cute, eh?), according to this Journal of Insect Science article, the Asian lady beetle is just better at it. Overall, they’ve made a positive impact in some areas of pest control, but are largely considered a model of the dangers and failure of introducing new species as biological controls.

An Asian multicolored lady beetle larva eating native lady beetle larva. Photo by Don J. Dinndorf, blogger on

The Sex and the Cannibalism

Through my research of the Asian Multicolored Lady Beetle, my conception of ladybugs as these adorable, charismatic creatures has certainly changed. But those are just the Asian Multicolored Lady Beetles right? Nope, ladybugs are just really weird, kind of disgusting and fascinating creatures. Here’s the evidence:  

  • When threatened, ladybugs begin to bleed from their knees. Their blood is full of toxic chemicals that make them taste bad to predators, so bleeding a little gives them a preview of the meal to come (learn more about ladybugs here).
  • Ladybugs have the most sexually transmitted infections of virtually any insect. In the words of Dr. Greg Hurst of the University of  College London, ladybugs are “remarkably promiscuous.”
  • Ladybugs are cannibals, especially when food sources are scarce. They feed on both sibling and non-sibling eggs.

Two ladybugs eating a dead ladybug. Photo by Maria F., WordPress blogger. You can read her story about this image by clicking the image.

*DISCLAIMER: The term “ladybug,” is actually a misnomer. Ladybugs are small beetles of the Coccinellidae family, and not true bugs (true bugs belong to the insect order Hemiptera). I often refer to these lady beetles as ladybugs because that is how they are colloquially known. 

Mosquitoes Suck.

After a month of living through Houston’s mosquito season, a single thought has consistently crossed my mind: are mosquitoes more attracted to me than others? I know it sounds crazy and perhaps self-centered, but I seem to consistently come away with more bite marks than those I am with.
PHIL Image 1969

Blood enlarged female mosquito. Photograph by James Gathany, CCD Public Health Image Library.

This week, I set off to find out once and for all if and why mosquitoes are attracted to some people more than others.

The good news is, I’m not crazy! Mosquitoes do seem to be attracted to some people more than others for various reasons. Unfortunately, the question of why can’t exactly be answered once and for all — at least with the information that is currently available. That isn’t to say though that scientists don’t have a good idea about what attracts mosquitoes to people and, perhaps more importantly, what repels them. 

Difficulties in Generalized Answers

It’s so hard to create generalizations about causes of attraction because of the differences among mosquito species that exist. Humans bodies also give off a lot of trackable information too (heat, movement, chemical compounds in body odor, etc.), making it that much more difficult to pinpoint a specific reason.

There are over 3,000 species of mosquitoes worldwide, and many species behave differently from each other in terms of aggressiveness, preferred prey, and the chemicals that they are more attracted to. For example, in a study from the Imperial College London (check it out here), scientists found that different baits were more attractive to different species. The baits used were carbon dioxide and human body odor — both known attractants of mosquitoes. They observed that all species tested were more attracted to both traps as bait concentrations increased, but that there was a difference in which of the baits attracted a larger portion of the mosquitoes across different species. This shows that although the generalization that mosquitoes are attracted to carbon dioxide and chemicals in human body odor can be made, this generalization doesn’t show how the strongest factor of attraction can be different for different species.

Mosquitoes also take into account many different factors when seeking blood, as Dr. Leslie Vosshall explains in an interview with The Daily Beast. First, the mosquito detects the smell of body odor and carbon dioxide (mosquitoes can detect carbon dioxide from 30-40 feet away). Then, as the mosquito moves closer, it is able to detect heat and movement. Finally, when the mosquito lands, it notices taste. Dr. Vosshall notes that in her own experience, mosquitoes will fly towards her and land on her, but then fly off without biting, highlighting the fact that taste can play a roll in mosquito attraction. 

What We Know

Although the complexity of the issue keeps us from a black or white type of answer, scientists do agree that certain things attract mosquitoes in general. For example, carbon dioxide (released from skin and by exhaling) and lactic acid (a chemical compound in skin that is especially present when exercising) have been shown to attract mosquitoes, as seen in the Imperial College study mentioned before.

However, these attractors don’t explain why some people get bitten more than others; we all emit CO2 and have lactic acid. Also, as Dr. Vosshall mentioned, it is only known that body odor and carbon dioxide are very important in a mosquito’s initial attraction.

Mosquitoes avoiding DEET (a mosquito repellent) treated hand on right. Photograph by Greg Allen, USDA-ARS.

Instead of focusing on analyzing what about a person makes them more attractive, researchers have begun to explore the possibility that some people emit extra, repellent chemicals that either mask or actively repel mosquitoes. Researchers at Rothamsted Research in the U.K. have collected and analyzed the body odors of known mosquito-attracting individuals and mosquito-resistant individuals and identified certain chemical compounds that were present in the resistant group but not the attractive group. Many of these chemicals are believed to be related to stress, but it is still not known if stress leads to less mosquito bites. You can read more about Rothamsted Research’s work here and here.

The answer to my question wasn’t as neat and specific as something like “eating bananas attracts mosquitoes” or “taking vitamin B-12 repels them” (both are just wives tales), but then again, nature wouldn’t be as exciting and beautiful as it is if all of the answers were that simple.

Other Cool Mosquito-Related Links