How to Catch a Bee

During my days as a summer camp unit director, one of my campers brought me a flower. When I looked closer, I realized this 11-year-old was not interested in the flower, but the bee and spider on top of the flower, head to head. I assumed they were fighting, but they were both pretty still, and it dawned on me that the bee was a goner, locked in the “jaws” of the spider, whom I figured had won the fight. I was still wrong, and the reality of this interaction is even cooler than I had imagined:

The spider hunts by hiding in flowers that attract their prey, the bees.

I posted my spider-bee-flower pic on Instagram recently, which received more interest than I had expected. I even had comments asking about the evolution of this flower-sitting ambush spider, so I looked it up, and I stumbled upon a cool chemical ecology story.

The first thing I learned is that, when given a choice, both the bees and this group of spiders, crab spiders, pick the same flowers. By covering the flower with saran-wrap and watching the spiders’ flower choice change, scientists were able to figure out that spiders are choosing their flowers by following chemical signals in the air, aka smells. This means these spiders are adapted to smelling out flowers that are more likely to attract their dinner.

Do bees fall for this trap? Bees not only fall for this ambush, but are more attracted to flowers with spiders than to safe, spider-free flowers.  Why would a bee fly closer to a purple flower that has a white, hungry spider in the middle?

Clearly, bees see differently from us. As I was perfecting my Instagram post, I was struck by my black and white Instagram filter, which showed the flower and spider as same shade of white (Figure 1). Even without extensive training in bee sensory biology, I figured there must be some sort of visual trick at play.

Figure 1. Screenshot of my Instagram post with 100% of the color saturation removed.

Too bad there is no UV filter on insta, because bees can see ultraviolet. Flowers take advantage of the bees’ visible spectrum in UV and often attract bees with target-like patterns, using dark UV spots in the middle. Darker UV target patterns can mean more pollination, so this trait is selected for in both flowers and bees.

So why are bees attracted to the crab spider flowers? Crab spiders have a layer of transparent cells covering spider skin cells that can change color! There are a few types of this pigment- the ommochrome pigment, which either allows spiders to or yellowish to red, or allows white spiders to have UV fluorescent patterns. With a UV pattern on their backs, flowers with spiders look like an extra dark flower target and attract bees more effectively than flowers without spiders.

Of course, natural selection goes both ways. Native bees in Australia fly close to, but can recognize and veer away from native crab spiders, whereas introduced honeybees have not adapted to recognize this danger.

Plants interact with insects and their predators. Scientists use the term “tritrophic interactions” to describe three trophic levels, or links in the food chain, interacting and affecting one another. As my thrilled camper and curious Instagram “fans” could pick up on, tritrophic interactions are fascinating! From an applied science perspective, knowing the intricacies of tritrophic interactions is essential to fully understand the side effects of potential global solutions in food security, and pest management, and conserving biodiversity.


Note: All the papers I cite in this post are by Dr. Astrid M. Heiling, who has many other fantastic papers. Check her work out!


Wings on Fire

I had always dreamed of going to the Amazon. The rainforest was a dream that breathed new life into me the way it breathes oxygen into the planet. As indescribable as the awe that comes from being amongst such biodiversity may be, the rainforest enchanted me in the movement of a toucan awkwardly wielding its beak, and in the flapping of wings on fire in the sunset as the faithful scarlet macaw streaks across the sky in its squeaky calling out to all below. Some moments brought forth vulnerabilities- the surprise of a snake’s delicate flicker of its tongue interrupting our gaze, and some brought forth grace, such as meeting the long-dreaded tarantula and experiencing not fear, but its majesty. Walls of rain sing in the rainforest upon giant sheets of leaves and dance on the surface of the turbid river. There is promise in the sunrise through the canopy mist, and in the sigh of achievement in the last orange glows on emergent branches, awaiting the stars and tree frog songs. I believe in this feeling of awe, and in its power.  Because of this, I live with more connection to the earth, more affinity for discovery, and more passion for sharing this awe with the global community. Dr. Kelly Swing, the director of the research station, quoted an Amazonian tribe leader in a presentation to visiting students, “We only know what we see; we only love what we know; we only care about what we love”. This has become my personal mission statement.

Some days I feel powerless. Numbers can be defeating—statistics on global carbon emissions, deforestation rates, biodiversity loss, increased poverty, inequality in human rights, and school shootings lead me to question whether I can have a positive impact. Science gives me hope; through science more people have a reason to care. My goal is to create research to discover new results, my findings will allow deeper understanding, and through understanding my work will facilitate an affinity for ecology. Through practice I know I have the power to connect as a science instructor and I have the power to connect across cultural boundaries. Of course I am still refining the art of connecting people from many different backgrounds to science, but luckily science inquiry is a task that always brings me joy.