SUBJECT: Ph.D. Dissertation Defense
BY: Elio Challita
TIME: Tuesday, May 9, 2023, 9:00 a.m.
PLACE: Ford ES&T, L1255
TITLE: Fast and Furious: Principles of droplets, jets, and damping in ultrafast Invertebrates
COMMITTEE: Dr. Saad Bhamla, Chair (ChBE)
Dr. David Hu (ME)
Dr. Simon Sponberg (Physics)
Dr. Sheila Patek (Biology)
Dr. Sughwan Jung (ME)


This thesis presentation delves into the world of tiny ultrafast organisms, specifically sharpshooters, springtails, and slingshot spiders, to explore the role of fluid dynamics in their rapid biological movements. In the first part, we investigate the fluidic, energetic, and biomechanical principles that enable sharpshooter insects (Hemiptera: Cicadellidae) to thrive on a nutrient-sparse xylem sap diet. We examine their remarkable superpropulsion strategy during droplet ejection through the temporal coordination between the stylus and the droplet. Employing experimental, mathematical, and computational approaches, we explore the physical limits of this unique droplet propulsion strategy and demonstrate why it is energetically favorable for these insects to fling their droplet excreta instead of using alternative mechanisms such as 'jetting' and 'dripping.' Using dimensionless analysis, we show how biological organisms living in a world governed by surface tension develop novel strategies to overcome capillary adhesion during fluidic ejection. In the second part of the presentation, we introduce a mathematical framework for the arrest and damping of ultra-fast movements in biological organisms. We contextualize and validate this framework through field and lab experiments on two organisms: the rapid launch of slingshot spiders (Araneae: Theridiosomatidae) and the controlled landing of semi-aquatic springtails (Arthropoda: Collembola) at the water-air interface. For slingshot spiders, we demonstrate how these organisms use their tension line and viscous drag to halt their ultra-fast movements. For springtails, we investigate the adhesive landing mechanisms employed by these creatures on water surfaces, revealing how collophore adhesion assists in controlling their upward movement after reaching maximum depth. By analyzing the movement of these extreme invertebrates through physics-based arguments, we unveil how these finely tuned ultrafast organisms harness their structure-fluid interactions to survive and fulfill their biological functions, including excretion, predation, and predator avoidance.