I want you to do me a favor. I want you to hit me as hard as you can.
What’s that? You want more background?
Folks, things have started to pick up. Perhaps the most important development since June 11th has been the christening of our two mantis shrimp, which will give me an excuse to talk about mantis shrimp anatomy. We have two mantis shrimp living in our humble makerspace, All Hands Active: Toothfinger and Featherclown.
Toothfinger’s name comes from his scientific name, Odontodactylus scyllarus. To break that down, “Odonto” means relating to a tooth or teeth (think dentist), and “dactylus” is related to a greek word for finger. Featherclown’s name comes from two common names for Odontodactylus scyllarus, the peacock mantis shrimp (peacocks having those big colorful feathers), and the harlequin mantis shrimp (harlequin meaning clown, not the Joker’s love interest).
Anyway, let’s get into the anatomy that gave Toothfinger his name: the second raptorial maxillipeds, or as scientists in the field call them, his raps. The raps are 4-part “fingers,” composed of a the merus (the “femur”), the carpus (think the carpal bones of the hand), the propus (the “tibia”), and finally the dactyl. I briefly mentioned the concept of power amplification in my first post. It’s the way mantis shrimp are able to store up and quickly release an immense amount of energy that a single muscle twitch cannot accomplish by itself. This energy is stored in a sort of “spring” embedded in its rap called the saddle.
The seminal work on this spring action, as well as the EMG work I cited in my last post, was done by Professor Sheila Patek. In addition to being a true science badass (podcast) and an alumnus of my school, UMass Amherst, she discovered the mechanism of power amplification in mantis shrimp. The saddle shape on the merus is known as a hyperbolic paraboloid, a shape that shows up in architecture and origami. Here’s a gif of my Starbucks paper bag—turned saddle, resisting deformation. This should give you a sense of how the saddle stores and releases energy. By using multiple twitches, the extensor muscle in the merus compresses the saddle further and further, twitch by twitch, until the energy is released by the flexor.
Facing the 3-inch long beasts
Having done recordings in several insects, I felt that I had enough data for a preliminary cross-species analysis of EMGs between insects and the mantis shrimp. Meaning that I had to face the prospect of touching Toothfinger and Featherclown, those murderous bastards. However, it turned out that the challenge wasn’t in keeping my fingers intact, but in getting the stomatopods to punch at all.
The juicy bits of mantis shrimp behavior happens inside of and around their burrow: they grab whatever comes too close to the opening, recede into their lair, and get to work opening up the shell with intermittent audible clicks. Some of the first work on mantis shrimp from the ‘60s detailed their territoriality. Most social interactions involve burrow eviction/defense, where one stomatopod has to demonstrate dominance over another individual who wants its to steal its digs, no pun intended.
So their striking is closely tied to their burrow. My first attempt to get them to punch involved making a behavioral chamber that simulated a burrow. No dice. Featherclown just sat there. Then, I tried copying Sheila Patek’s restraint paradigm from her EMG paper, and again we encountered a distinct lack of dice. Odds are I’d have to invest a lot of time in habituating the animals to a restraint setup, plus it’s not burrow-like at all.
I was feeling a bit lost, and then I noticed another paper from the Patek lab had come out on this year with a methodological stroke of genius: just use the actual burrow! In the lab, a mantis shrimp burrow is usually an ~6-inch long PVC pipe. Why not open a window lengthwise along the pipe, and place the window against the glass?
All that was left was to see if they’d strike from their new burrow, so I stuck my hand into the tank.
Holy reliability, Batman! If spaced out by a minute or two, I can pretty much elicit a strike every time. Here’s a fun thought experiment: what does it mean to the mantis shrimp that I put my finger near his burrow and the pull it back when he strikes every minute or so for a period of time?
Crane, R. L., Cox, S. M., Kisare, S. A., & Patek, S. N. (2018). Smashing mantis shrimp strategically impact shells. The Journal of Experimental Biology, 221(Pt 11), jeb176099. https://doi.org/10.1242/jeb.176099
Dingle, H., & Caldwell, R. L. (1969). The Aggressive and Territorial Behaviour of the Mantis Shrimp Gonodactylus Bredini Manning (Crustacea: Stomatopoda). Behaviour, 33(1–2), 115–136. https://doi.org/10.1163/156853969X00341
Patek, S. N., Korff, W. L., & Caldwell, R. L. (2004). Biomechanics: Deadly strike mechanism of a mantis shrimp. Nature, 428(6985), 819–820. https://doi.org/10.1038/428819a
Kagaya, K., & Patek, S. N. (2016). Feed-forward motor control of ultrafast, ballistic movements. Journal of Experimental Biology, 219(3), 319–333. https://doi.org/10.1242/jeb.130518