Confuse to survive – the mimics

Geetha Iyer

Mimicry is a survival technique practised by all living organisms including humans. Humans use manufactured materials to mimic and camouflage themselves; the non-human world is all about being organic. The animal kingdom abounds with numerous examples of mimics that share our spaces, confuse us so well that either we miss them or mistake them – because they are such good mimics. I introduce you to those that are common examples in a biology lesson, yet hidden among them are also some uncommon ones that can be completely missed if one is not alert and observant.

The praying mantis that is not a stick insect
Stick and leaf insects are the most common examples given to students in a biology class. Yet I wonder how many have actually seen a stick insect to be able to recognize one, or even less a leaf insect. Probably a bleached specimen inside a formalin filled jar or a garish image in a book. So teachers, take your students out and try this fun-filled classroom activity, I have titled as “Insect Cons”

A common insect in most habitats across India, especially South India, is this preying mantis that is often mistaken to be a stick insect. It is only in external appearance that it looks like a stick insect. A closer examination will reveal that its front pair of legs is held up folded together in the classical ‘praying position’ that gives mantids the other common name, i.e., praying mantis. Observation will also reveal other features, several spines on the front pair of legs that are never there on a stick insect. The way the legs are held by a stick insect is quite different from the way a praying mantis holds its leg. Another feature is the head. Quite distinct and different in shape and the way they are articulated and held can clearly tell you whether you are looking at a mantid or a stick insect. This preying mantis is a common visitor to most gardens. The stick insect is not so easily seen. Many of them are nocturnal creatures, best seen at night when they emerge to feed or at dawn or dusk. Stick insects can also pretend to be dead if they sense danger. This kind of deception is known as thanatosis.

A longhorned grasshopper that is not a leaf insect
The grasshopper is a well-known insect in biology classes and it is shown in textbooks coloured green. For insects that graze on leaves it is a safe colour for camouflage which is why many phytophagous insects sport green. But some are not satisfied with mere camouflage and add a dash of mimicry to hide themselves. Some make themselves look like leaves. Ask students to give you features that they would expect to see on a leaf insect. Lest they forget, remind them that a leaf insect is an insect and so their description must match closely with the basic body structure of an insect. Let not their imagination run away with them. Now show them the two images that are given here and ask them what they would call these two insects.

Living amongst the plants are these insects called as tettigonids or the longhorned grasshoppers. Some species are commonly called katydids, which is a reference to their call that sounds as if they are saying ‘katy-did, katy-didn’t’ repeatedly. Among these tettigonids is a kind that is not only green, but its wings are patterned to resemble the veins of a leaf. It often sits with its wings flattened around and above its body to resemble a leaf. Many mistake it to be a leaf insect. A true leaf insect belongs to a completely different order of insects and is closely related to the stick insect; whereas the longhorned grasshopper, as the name suggests, is a relative of the commonly seen grasshopper. Leaf insects are not easy to spot and can be seen only in forests, whereas the leaflike tettigonid is a common visitor in our gardens. Tettigonids are jumpers and have distinct calls. The leaf insect is a slow mover and does not call.

The bug and the beetle
Bug is a word indiscriminately used by Americans and others in the English speaking parts of world to describe any small creature that creeps, crawls or flies. Bugs are a specialised kind of insects that belong to the order Hemiptera. These insects inflict the greatest of harm to plants. There are many hemipteran bugs that look like and therefore, mistaken to be beetles. There is a green coloured bug that can be commonly seen across India. This shiny and brightly coloured insect is invariably mistaken for a beetle. A closer examination will show you that it is not a beetle. The outer wings (forewing) of a beetle are hardened to form what is called an elytra. In the case of the bug too, the forewings are thick, but not all of it. In most Hemipteran bugs the lower part of the forewings are membranous whereas the upper parts are hardened as seen in beetles.

Chrysocoris sp is a green coloured bug that can be found on Ipomoea plants (Railway creeper). In this bug the forewings are completely thickened and brightly green and it is often mistaken for a beetle.

There are several more commonly seen insects that are mimics. The world of the butterfly is full of them. This article is merely to give you an introduction to what you are likely to find if you step out into the field with your students.

If your school happens to be in a green area take the opportunity to take your students out on a different kind of field trip. Print out the images of insects given in this article and put it up on the notice board. Call it a Sherlock Holmes activity; cook up a nice story to discover a set of insects in the field and students will enjoy being young detectives, sleuths on the trail of the stick insect, a praying mantis, a moth, a butterfly, a fly or a bee. Such an activity will result in your students learning a lot more about the natural world than you can hope to teach in class. It will also enhance their observation, thinking and reasoning skills; provide you with an opportunity to improve their reference and research skills. Try it and you are sure to find an enjoyable lesson where you are able to introduce a variety of topics from your syllabus and provide an opportunity to students to learn from real life.

References

• https://rps-science.org/slideshow/photographer/4927/ – slide show on stick insect
• www.eol.org – Reference site for commonly seen insects

Insect Cons

Give students the following information at the beginning: Stick and leaf insects are true insects. Their visible characteristics are i) three pairs of legs – each leg having two claws and a pad for climbing and clinging on to leaves; ii) two pairs of wings (most females are wingless, males fl y); iii) body divided into head, thorax and abdomen. They have antennae, compound eyes and breathe through spiracles. Males are very much smaller than the females. As their name suggests they are excellent mimics of plant parts, especially the stem.

If you are in the school garden, you could begin by spending five minutes trying to find the insects that are given here below this box.

Ask students:
• To draw a male and female stick insect as they would imagine them to be.
• If they need more information to draw the insect.

Next, give them a printout of the two images (Preying mantis and stick insect) that accompany this article. Discuss to find out if they are both stick insects? Are they both mimics? Why do they mimic, specifically what advantage does it provide? What do they infer/conclude about their own imagination of the stick insect after seeing the images.

The author is a consultant for science and environment education. She can be reached at scopsowl@gmail.com.