Deimatic Displays - Startling Signals

In ethology, threatening or starting behavior is called deimatic behavior. The term was coined by Malcolm Edmunds, emeritus professor of zoology at the University of Central Lancashire, England.

It is similar to aposematism, and scientists often disagree on what makes one signal deimatic and what makes another one aposematic. Some say certain signals can be both deimatic and aposematic. The true difference is that while deimatic behavior is meant to startle, aposematic displays are meant to warn the receiver, and while the former does not result in negative reinforcement, the latter does - the predator learns to avoid aposematic prey. The former is a bluff, the latter is a genuine signal of the prey's toxicity or other ability to defent itself.

Deimatic behavior can be understood as a rather dynamic response. Usually the prey is defenseless - it's minding its own business in an unconspicuous state. Performing a rapid, dynamic startling display is its only chance to confuse the predator and earn precious time to flee.

Some argue that deimatic behavior may only occur before the attack, while others have proven that in some animals, such as katydids, deimatic behavior may, in fact, happen after an attack, which stops the predator from continuing the attack.

No matter how we define 'true' deimatic displays, we should just see what one looks like.

Examples:

Bluetongue skinks (genus Tiliqua) are known for showing their blue tongues in defensive displays. A 2018 article published in Behavioral Ecology and Sociobiology explores the deimatic behavior in northern bluetongue skinks (Tiliqua scincoides intermedia).

The authors of the study found that the skink makes a 'full-tongue display' (i.e. it reveals the entire tongue) only during the final stage of predation, that is, in the moment when it feels it's in the greatest danger. The skink combines the display with hissing, rapid body movement and body inflation to make it even more startling. The reason for such timing, according to the authors, could be to "overwhelm the sensory system of the receiver" - it's a shock! If it decides to activate this behavior at an earlier stage, the skink could make itself more conspicuous to a predator that would have possibly ignored it, had it not acted.

The signal could be especially effective on birds and reptiles for a reason we would never understand without technology - the tongue is UV-blue! What's more, the deeper part of the tongue (the part that's only visible during the 'full-tongue display') is nearly twice as luminous as the tip! The authors, however, aren't convinced that the UV coloration of the tongue has anything to do with making the display more startling, but that it is merely a by-product of the skink's tongue histology. To know for sure, we need to study predator responses to this behavior.

The skink's behavior could be seen as aposematic if the reptile also attacked the predator, making the 'full-tongue display' a signal that means "don't continue because you'll get hurt!" During the study, however, the animals did not attack, so the authors concluded that the behavior agreed with the 'dematic behavior theory'. The signal is meant to startle, not to warn.

Common name:	Devil's flower mantis
Scientific name:	Idolomantis diabolica
Phylum:	Arthropoda
Class:	Insecta
Order:	Mantodea
Family:	Empusidae
Scientific reading:

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Scientific name:	Physalaemus nattereri
Phylum:	Chordata
Class:	Amphibia
Order:	Anura
Family:	Leptodactylidae
IUCN status:	Least concern
Population trend:	Decreasing
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Scientific name:	Papilio machaon
Phylum:	Arthropoda
Class:	Insecta
Order:	Lepidoptera
Family:	Papilionidae
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