Small organisms can produce powerful, sub-millisecond impacts by moving tiny structures at high accelerations. We developed and validated a pendulum device to measure the impact energetics of microgram-sized trap-jaw ant mandibles accelerated against targets at 10⁵ m s^-2. Trap-jaw ants (Odontomachus brunneus; 19 individuals; 212 strikes) were suspended on one pendulum and struck swappable targets that were either attached to an opposing pendulum or fixed in place. Mean post-impact kinetic energy (energy from strike converted to pendulum motion) was higher with a stiff target (21.0-21.5 µJ) than a compliant target (6.4-6.5 µJ). Target mobility had relatively little influence. Mean contact duration of strikes against stiff targets was shorter (3.9-4.5 ms) than against compliant targets (6.2-7.9 ms). Shorter contact duration was correlated with higher post-impact kinetic energy. These findings contextualize and provide an energetic explanation for the diverse, natural uses of trap-jaw ant strikes such as impaling prey, launching away threats, and performing mandible-powered jumps. The strong effect of target material on energetic exchange suggests material interactions as an avenue for tuning performance of small, high acceleration impacts. Our device offers a foundation for novel research into the ecomechanics and evolution of tiny biological impacts and their application in synthetic systems.

Tracks: tracks.zip

These are the outputs from the automated digitizing routine. Each file has the A#**#.csv naming scheme where the A# stands for the ant number, the ** specifies the target type (C = Compliant, S = Stiff, FC = Fixed Compliant, FS = Fixed Stiff), and the last # represents the strike number. In each file, the column titles are as follows:

pt1_cam1_X: The x coordinates for the ant pendulum immediately after impact
pt1_cam1_Y: The y coordinates for the ant pendulum immediately after impact
pt2_cam2_X: The x coordinates for the target pendulum immediately after impact (note that this column does not exist for the fixed targets as the target does not move after impact)
pt2_cam2_Y: The y coordinates for the target pendulum immediately after impact (note that this column does not exist for the fixed targets as the target does not move after impact)

Verification impactor dataset: mICP_Impactor_Dataset.csv

This contains the dataset of impacts with the verification impactor as the energy source. Information included is as follows:

group: Specifies the target type where C = Compliant, S = Stiff, FC = Fixed Compliant, and FS = Fixed Steel   
strike: Strike number - specifies the order of the observation in the amount of strikes performed by the ant for this target type  
initial: The amount of energy delivered by the swinging impactor pendulum measured in Joules. Calculated by finding the velocity of the impactor right before impact with the target 
tke: The kinetic energy of the target's pendulum after the impact measured in Joules
ike: The kinetic energy of the impactor's pendulum after the impact measured in Joules  
pike: Post-impact kinetic energy calculated by adding the kinetic energy of the target's pendulum after impact and the kinetic energy of the impactor's pendulum after impact (tke + ike). Measured in Joules.  

Live trap-jaw ant dataset: mICP_Brunneus_Dataset.csv 

This contains the dataset of impacts with live trap-jaw ants as the energy source. Information included is as follows:

ant: Specifies which ant is performing the strike     
group: Specifies the target type where C = Compliant, S = Stiff, FC = Fixed Compliant, and FS = Fixed Steel  
strike: Specifies the order of the observation in the amount of strikes performed by the ant for this target type  
seq: Specifies the order of the observation in the total amount of strikes performed by the ant across all target types  
duration: The amount of time in seconds during which the mandibles were in contact with the target   
ake: The kinetic energy of the ant's pendulum after the impact measured in Joules   
tke: The kinetic energy of the target's pendulum after the impact measured in Joules  
pike: Post-impact kinetic energy calculated by adding the kinetic energy of the target's pendulum after impact and the kinetic energy of the ant's pendulum after impact (ake + tke). Measured in Joules.   
ratio: The ratio of ake to tke. Note that for impacts against fixed targets, the target remains stationary after the impact and therefore the tke is NA  
dist: The distance (in millimeters) between the ant and the target before the strike  

Annotated Rcode: mICP_DataAnalysis_R_Code.Rmd

This Rcode was used to analyze the verification impactor dataset and the live trap-jaw ant dataset.

CAD files: mICP_CAD.zip 

The folder contains the necessary CAD files (in .stl format) to 3D print the pendulum housings for the mICP as well as the axel insert described in the publication.