IELTS Online Practice Materials

Mantises

(A) Mantises are an order of insects that contains over 2,400 species and about 430 genera in 15 families. Mantises are distributed worldwide in temperate and tropical habitats. They have triangular heads with bulging eyes supported on flexible necks. Their elongated bodies may or may not have wings, but all have fore legs that are greatly enlarged and adapted for catching and gripping prey; their upright posture, while remaining stationary with forearms folded, has led to the common name praying mantis.

(B) They are mostly ambush predators, but a few ground-dwelling species are found actively pursuing their prey. They normally live for about a year. In cooler climates, the adults lay eggs in autumn then die. The eggs are protected by their hard capsules and hatch in the spring. Females sometimes practice sexual cannibalism, eating their mates after copulation. Occasionally, the females decapitate the males just before or during mating.

(C) The mating season in temperate climates typically takes place in autumn, while in tropical areas, mating can occur at any time of the year. To mate following courtship, the male usually leaps onto the female's back, clasping her thorax and wing bases with his fore legs. He then arches his abdomen to deposit and store sperm in a special chamber near the tip of the female's abdomen. The female lays between 10 and 400 eggs, depending on the species.

(D) Eggs are typically deposited in a frothy mass-produced by glands in the abdomen. This froth hardens, creating a protective capsule, which together with the egg mass is called an ootheca. Depending on the species, the ootheca can be attached to a flat surface, wrapped around a plant, or even deposited in the ground. Despite the versatility and durability of the eggs, they are often preyed on, especially by several species of parasitic wasps.

(E) As in closely related insect groups in the superorder dictyoptera, mantises go through three life stages: egg, nymph, and adult. For smaller species, the eggs may hatch in 3–4 weeks as opposed to 4–6 weeks for larger species. The nymphs may be coloured differently from the adult, and the early stages are often mimics of ants. A mantis nymph grows bigger as it molts its exoskeleton. Molting can happen 5 to 10 times before the adult stage is reached, depending on the species. After the final molt, most species have wings, though some species remain wingless particularly in the female sex. The lifespan of a mantis depends on the species; smaller ones may live 4–8 weeks, while larger species may live 4–6 months.

(F) Sexual cannibalism is common among most predatory species of mantises in captivity. It has sometimes been observed in natural populations, where about a quarter of male-female encounters results in the males being eaten by the female. Around 90% of the predatory species of mantises participate in sexual cannibalism. Adult males typically outnumber females at first, but their numbers may be fairly equivalent later in the adult stage, possibly because females selectively eat the smaller males.

(G) The reason for sexual cannibalism has been debated; experiments show that females on low quality diets have a higher chance to engage in sexual cannibalism compared to females on high quality diets. Some consider that submissive males gain a selective advantage by producing offspring. This theory is supported by a quantifiable increase in the duration of copulation among males which are cannibalized, in some cases doubling both the duration and the chance of fertilization. This is contrasted by a study where males were seen to approach hungry females with more caution, and were shown to remain mounted on hungry females for a longer time, indicating that males that actively avoid cannibalism may mate with multiple females. The same study also found that hungry females generally attracted fewer males than those that were well fed. The act of dismounting after copulation is dangerous for males, for at this time, females most frequently cannibalise their mates. An increase in mounting duration appears to indicate that males wait for an opportune time to dismount a hungry female, who would be likely to cannibalise her mate.

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Adapted from Wikipedia