Cicadas Use Darkness to Climb Trees | Skototaxis Explained

Here in Chicago, as spring tentatively unfurls along the Magnificent Mile and through Lincoln Park, it’s easy to gain lost in the blossoming cherry trees and the return of migratory birds. But a fascinating piece of recent research reminds us that even the most seemingly simple natural behaviors are underpinned by surprisingly complex mechanisms. Scientists have discovered that cicadas, those iconic harbingers of summer, don’t just randomly climb trees; they actively seek out darkness – the shadows cast by the exceptionally branches they intend to inhabit. This behavior, known as skototaxis, adds another layer to our understanding of these remarkable insects and raises engaging questions about how animals navigate their world.

The Science of Shadows: How Cicadas Find Their Perches

The study, recently highlighted by Science News, reveals that cicadas use the contrast between light and shadow as a primary cue for upward movement. This isn’t about simply avoiding bright light; it’s about actively *seeking* the darkness created by the tree canopy. Researchers believe this strategy is particularly crucial for newly emerged cicadas, whose wings are still developing and require a stable perch to dry and harden. Imagine a newly emerged cicada, struggling to gain purchase on a smooth surface. Finding a shadowed branch offers not only a safe haven but also a visual guide for its ascent. It’s a beautifully elegant solution to a challenging problem.

Skototaxis isn’t unique to cicadas. Many insect species exhibit this behavior, often as a means of finding shelter or avoiding predators. However, the specific application of shadow-seeking for tree-climbing in cicadas is particularly noteworthy. It highlights the importance of visual cues in insect navigation and demonstrates how animals can exploit environmental features to their advantage. The research also prompts us to consider how changing light conditions – such as those caused by urban light pollution or deforestation – might impact cicada behavior and, their survival. The Illinois Ornithological Society, for example, has been tracking the impact of light pollution on migratory bird patterns for years, and this cicada research offers a parallel for insect behavior.

Cicadas in the City: A Chicago Perspective

Chicago, with its mix of dense urban landscapes and sprawling green spaces like the Cook County Forest Preserves, provides a unique environment for observing cicada behavior. While the periodical cicadas that emerge in massive broods aren’t common in the immediate city center, their presence is felt in the surrounding suburbs. The last major emergence in 2007 was a memorable event for many Chicagoans, with the sheer volume of insects creating a deafening chorus. Understanding how these insects navigate and find suitable perches is crucial for predicting their distribution and potential impact on local ecosystems.

The University of Illinois at Chicago (UIC) has conducted extensive research on urban ecology, including studies on insect populations in Chicago parks. Their perform demonstrates that even in highly urbanized areas, insects play a vital role in pollination and nutrient cycling. The discovery of skototaxis in cicadas adds another dimension to this understanding, suggesting that even seemingly simple urban features – like the shadows cast by buildings – can influence insect behavior. The Chicago Park District actively manages tree canopies throughout the city, and understanding cicada preferences could inform future planting strategies to support these important insects.

The impact of climate change on cicada emergence patterns is also a growing concern. Warmer temperatures could potentially alter the timing of emergence and disrupt the synchronicity between cicadas and their host trees. The Illinois Department of Natural Resources (IDNR) is actively monitoring insect populations across the state to track these changes and assess their potential consequences. This research into skototaxis provides a valuable tool for understanding how cicadas might adapt to a changing environment.

Navigating a Cicada Season: Local Resources in Chicago

Given my background in ecological research, if you find yourself experiencing a significant cicada emergence in the Chicago area, or simply want to learn more about these fascinating creatures, here are three types of local professionals who can provide valuable assistance:

Arborists specializing in tree health:

Cicada egg-laying can sometimes cause minor damage to tree branches. A qualified arborist can assess the health of your trees and recommend appropriate pruning or treatment to minimize any potential harm. Look for arborists certified by the International Society of Arboriculture (ISA) and with experience working with local tree species.

Pest Control Professionals (Integrated Pest Management Focus):

While generally not harmful, large cicada populations can be a nuisance. If you’re concerned about the impact of cicadas on your property, a pest control professional specializing in integrated pest management (IPM) can offer environmentally responsible solutions. Avoid companies that rely solely on broad-spectrum pesticides.

Entomologists or Wildlife Biologists (Consultation):

For those truly fascinated by cicadas and their behavior, consulting with a local entomologist or wildlife biologist can provide in-depth insights. These professionals can offer expert advice on cicada identification, life cycles, and ecological roles. Check with local universities or nature centers for potential consultants.

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