Insects, because of their small size, cannot put up a fight against an attacking bird. However, they have developed some innovative ways of protecting themselves.
Insects defend themselves from predators by running away, hiding, camouflaging, crypsis, mimicry of poisonous insects, and even causing small explosions.
Insects have numerous enemies, including birds, mammals, and other insects. Most studies on insect defense have been concerned with how insects protect themselves against birds.
An insect’s first and best line of defense is to hide. Many species do this by restricting their movements to the hours of darkness when most birds cannot see them. Most will stay concealed during the day, burrowing or creeping under debris and into crevices.
Flying insects are much easier to spot at night. Many night-flying moths hide during the day in long grass or under low bushes, and many can be seen hiding during the day in garden trees and bushes
Butterflies that overwinter in the adult winged stage of their lives, such as the comma and the tortoiseshell, can also be seen hiding among vegetation or in hollow trees, sheds, or garages.
Insects living among the foliage of trees and bushes are surrounded by green leaves and brown twigs. Insects that hide in the leaves are almost always brown or green. Those that are found around the leaf litter are almost always brown or black. Camouflage is sometimes the best way to avoid being an easy meal.
The next stage in the elaboration of camouflage is the disruptive pattern. In the military, planes and tanks are often painted with irregular patterns of dark and light green.
These patterns break up the outline, helping them to stay concealed. These patterns can be seen in larger mammals such as zebras and giraffes. While not as predominant in insects, the patterns usually relate to their habitat.
The oak beauty moth has a band running across its forewings to break up the head shape while its wings closely mimic the bark of the trees it rests on.
Countershading is another technique used by many larger caterpillars. Light, under natural conditions, comes mainly from the sun above, and a rounded body tends to give away its shape when lit from above and shaded below. Some insects counteract this by having a darker top half and paler underneath.
The caterpillar of the eyed hawk-moth is an interesting example of this countershading, being dark green underneath and light green on top. Since its normal resting position is upside-down, this reversed countershading allows it to stay camouflaged.
Grasshoppers have excellent camouflage among the grass stems as they have brown and green streaks down their body. Crickets are often either brown or green, depending on whether they mainly live on the ground or on foliage.
How Do Insects Defend Themselves When Resting?
Butterflies and moths have various resting positions, which make their camouflage even more impressive. The comma butterfly, for example, closes its wings while resting so that it resembles a dying leaf.
The lappet moth also hides among dead leaves, helped by its reddish-brown wings and disguising its shape with the help of its hindwings.
One of the most amazing kinds of camouflage is adopted by the stick caterpillars of some geometer moths. Their bodies are colored and patterned to resemble the twigs of the trees and bushes on which they feed, often even having bumps on their backs to represent buds.
When they are not walking or feeding, these caterpillars adopt a rigid pose, clasping a twig with two pairs of abdominal feet to resemble growing twigs. They are hard to find for us even if we are looking for them, so must be even more difficult for a bird.
Several brightly colored insects, which do not attempt to hide or camouflage themselves, would appear to be sitting targets for hungry birds, yet birds are not interested.
While many of these insects appear beautiful, the message their coloration conveys to predators is a warning. Nearly all are distasteful or poisonous and therefore inedible.
In dry open spaces, such as chalk downland and sand dunes, where there is little cover for concealment, brightly colored burnet moths are often seen flying about and resting on flowers in the sunshine.
Although brightly colored, nearly all birds ignore them. If a young or inexperienced bird dares peck at a burnet moth, it immediately drops it and then exhibits signs of distress, salivating and wiping its beak. In this instance, it will learn to never touch another burnet moth.
Burnet moths do not only taste unpleasant but are also poisonous since they contain hydrocyanic acid and various histamine substances. The burnet moth contains cyanide.
The magpie moth, a white species with black and yellow markings, is another common insect that displays its warning on its body. These have a bitter flavor, something a well-known entomologist knows only too well after trying them in their different life stages.
Some species of caterpillar protect themselves with a coat of hairs, which may be extremely thick, as in tiger and ermine moths, and are also poisonous. The hairs on the caterpillar of the brown-tail moth are capable of causing a severe and irritating rash on human skin.
Butterflies and moths are not the only insects that adopt these fearsome tactics. The bugs of the suborder Heteroptera taste and smell extremely unpleasant, a fact you soon discover when around them.
Some, such as the well-known ladybirds (which secrete a vile-smelling liquid) and the rare black and red Lygaeus equestris, have warning colors, but many species are green and brown, appearing to use camouflage as a first line of defense and their foul taste as a final defense.
Wasps display a striking coloration in the form of yellow and black stripes, which inform potential predators of their capacity to sting. A rather unexpected feature of this is that, as well as being armed with a dangerous sting, they also taste really bad.
The distinctive coloring of wasps has come to be recognized by birds as a danger signal, and wasps are therefore left well alone.
This has led to the development of an extraordinary phenomenon in the insect world. A large variety of completely harmless insects have evolved markings and colors similar to wasps.
They gain a distinct protective advantage from this resemblance, which is known as insect mimicry.
Some smaller moths and caterpillars that rest on leaves are colored white or black to resemble bird droppings. It is not known whether they are trying to hide, resemble something unpleasant, or use mimicry, but it certainly works as a way of defense.
The bombardier beetle has the most remarkable defense mechanism, consisting of minor explosions emitted from the beetle’s rear.
Chemical substances called hydroquinone, and hydrogen peroxide is secreted into a reservoir near the beetle’s rear end, which opens into a combustion chamber.
When alarmed, the beetle passes the mixture into the combustion chamber, together with catalytic enzymes, which cause the two substances to combine in a chemical reaction.
This produces water, oxygen, caustic quinones, and enough heat to vaporize some of the liquid so that the charge is blasted out as a boiling hot corrosive spray. Ten to twenty discharges will deter even the most persistent predators.