Good morning insect lovers, last week we start the series of articles on insect behavior and predation. Check the first article Insect behavior: Are moth larvae predators?
Below you can find the chapter 2: How predators’ presence influence the moth’s behavior ?
The risk of being hunt influences the foraging behaviour in insects
Moths, as most Lepidoptera and insects in general, must deal with many predators such as birds, reptiles and small mammals. Living their ordinary life, both adults and larvae can be hunted and killed at any time. Because of that, it is evident that those animals live a risky life. Deciding where and when to eat becomes a key choice that influences larval and adult behavior of an insect. At any time, a prey balances their energy income with the risk of being killed by a predator. In other words, if there are nearby predators, it is unfavourable to forage in the dangerous area, even if resources are abundant.
Insect anti predators defenses
The anti-predatory defences include those characteristics that allow the prey to avoid being both seen, selected and captured by predators. They can be either constitutive or behavioural. Following a brief explanation of both cases.
The anti-predatory behaviors include those that help the prey to be undetected or to spot predators before they do. In addition, those anti-predatory behaviors prevent the attack or let the prey flee once attacked.
As an example, Lepidoptera caterpillars with cryptic colors are generally quite static insects, remaining motionless during the daytime. They eat only when the presence of predators is minimal. Thus, some species are predominantly nocturnal. Species with aposematic colours (such as Acherontia or Hyles) usually feed on top of the host-plant, where the leaves are more tender and young. Caterpillars absorb direct sunlight to grow faster. Due to their aposematic colours the risk of being hunted while eating is low.
“I can get on stage, in plain sight! As predators know I’m toxic.” That’s what a caterpillar is telling predators warning them.
The constitutive defences are defined and intrinsic characteristics of the organism, such as mimicry or aposematic colorings. Many moth species use cryptic colorations. Caterpillars showing this kind of colouring are often nocturnal and static. In fact, avoid being seen is their main purpose. A classic example is Laothoe populi, the poplar hawk moth.
As the other Smerinthinae species, the larva stay still, positioned on the underside of a poplar or willow leaf, in the medium-high part of isolated trees’ canopy or shrubs. Caterpillars don’t move or roam too much, they forage only when their main predators (birds) are not active.
Flash effect, the case of the death’s head hawk moth
Cryptic coloration is often associated with bright colors. Many other species, such as Acherontia atropos, the death’s head hawk moth, have both cryptic and flash colorations. The adults of the death’s head hawk moth show cryptic homogeneous colouration while resting. Once disturbed, the moth reveals their hind wings with an intense yellow colours and then flies away.
Flash colorings distract and disorient the predator, giving the prey enough time to escape.
In the same way, there are species (such as Macroglossinae) which have developed characteristics resembling a predator, often a snake or a lizard. These features include a set of aposematic colors and shapes.
Daphnis nerii larvae, the oleander hawk moth, presents two large ocelli in the anterior segments of their body, mimicking the eyes of a potential predator or larger animal. The larva contracts them when feels in danger, giving the appearance of a small snake to deceive predators. Larvae play on symmetry and contrasts to distort their image as much as possible. The ocelli of many species (like Deilephila) in the anterior part of the body are often associated with smaller ones and horizontal lines in order to befog predators.