Hexapoda 2 (insects)

Cimex lectularius, bed bug

The Apterygote (wingless) insects

These are the Diplura (bristletails), Collembola (springtails), Protura and Thysanura (silverfish).

The bristletails and silverfish both have two long cerci, and between this a caudal appendage. There are just under 10 000 described species of Apterygotes.

Class Pterygota (winged) insects

These insects have two pairs of wings; one pair on the mesothorax and another on the metathorax. Pterygotes have muscles which allow them to close their spiracles so greatly reducing water loss and enabling them to colonize drier habitats.

The Pterygotes can be further divided into two groups; those that undergo complete metamorphosis (holometabolous). A typical holometabolous insect the brown house moth, Hofmannophila pseudospretella shown on the right in the various stages of its life. And those that undergo a gradual metamorphosis (hemimetabolous).

Hemimetabolous insects have young that resemble the adults, and the gradual development of wings is external . Such insects include, Cimex lectularius (the bed bug) above, which shows the gradual change to the adult form, also Odonata (dragonflies), Orthoptera (grasshoppers), Dermaptera (earwigs) and Hemiptera (aphids, cicadas.

Holometabolous insects have young (larva) that usually do not resemble the adult (see above), and often occupy a different niche. These insects form a pupa (see above) before emerging as the adult form.

About 88% of the described insects are holometabolous and include the four largest Orders that have diversified along with the diversification and radiation of the Angiosperms; they are the Diptera (flies), Coleoptera (beetles), Hymenoptera (wasps, ants, bees), and Lepidoptera (butterflies and moths).

Hofmannophila speudospretella, brown house moth

Insects as vectors of diseases in humans

Disease Insect vector
Malaria Anopheles mosquito (Diptera)
Yellow fever Aedes aegypti Mosquito (Diptera)
Filariasis Culex mosquito (Diptera)
Typhoid House fly (Diptera)
Dengue Aedes mosquito (Diptera)
Sleeping sickness Tsetse fly (Diptera)
Plague Fleas (Siphonaptera)
Typhus fever Louse (Anoplura/Siphunculata)
Chagas Rhodnius (Hemiptera)

Insects as pollinators.

  • In the US alone insect pollinated crops were worth $20 billion at 2000 prices.
  • Every third mouthful of food we eat comes directly or indirectly from crops that have been pollinated by bees.

Importance of insects

Insect behaviour patterns.

Courtship. This usually involves males trying to attract females. The female behaviour is simply to accept or reject, e.g. during courtship the male scorpion fly presents the female with a dead insect which she eats during copulation.

Copulation. Copulation is the physical joining of the male and female culminating in the passing of sperm from the male to the female, e.g. bumblebees.

Egg-laying. Most species have very specific site requirements for egg-laying, so that the eggs are laid on, in or near the source of food for the larva or nymph, e.g. dung beetles.

Defence. Defence can be active, e.g. sting (bees, wasps, etc.), bite (beetles, etc.), chemicals (bombardier beetle); or passive e.g. hiding (cockroach), camouflage (stick insect).

Communication. Communication is the transfer of information between individuals - usually of the same species, e.g. honeybees communicating the location of a good food source.

Grooming. This is especially important in hairy insects, e.g. bumblebees. These and all others need to keep their antennae, eyes, wings, legs and mouthparts clean. Most have a brush or comb on their forelegs, e.g. bumblebees, that can be used to cleans antennae and legs.

Insect records

Fastest flight Austrophlebia costalis (Odonata: Aeshnidae), a dragonfly at 98 km/h
Hybomitra hinei wrighti (Diptera: Tabanidae), a fly at 145 km/h
Fastest wing beat Forcipomyia sp. (Diptera:Ceratopogonidae), a midge, species not known can beat its wings 1046 times per second.
Fastest runner Cicindela hudsoni, an Australian tiger beetle can run at 2.5 metres per second.
Least specific vertebrate blood sucker Glossina palpalis (Diptera: Glossinidae), tsetse fly. It can feed on any vertebrate.
Longest Pharnacia serratipes, a stick insect, at 55.5 cm (22 in).
Smallest adult Dicopomorpha echmepterygis (Hymenoptera: Mymaridae), a parasitic wasp. The length of the male is 139 µm.
Largest swarm <Schistocerca gregaria, the desert locust. In 1954 a swarm covering 200 km sq invaded Kenya. The swarm was estimated to contain 10 billion individuals.
Largest eggs Xylocopa auripennis, a carpenter bee lays eggs 16.5 mm long and 3.0 mm in diameter.
Heat tolerant Cataglyphis bicolor (Hymenoptera: Formicidae), a Saharan ant which can forage at body temperature above 50oC and surface temperature of up to 70oC.
Cold tolerant Polypedilum vanderplanki (Diptera), an African chironomid (midge) can survive submersion in liquid helium at -270oC.
Most spectacular mating Apis mellifera (Hymenoptera), the honey bee. The drone (male) dies after mating once. The queen bee files off with his phallus still in her vagina. The phallus having broken off after sperm exits explosively. The queen eventually ejects the phallus and goes on to mate again.
Longest regular migration Danaus plexippus (Lepidoptera: Danaidae), the monarch butterfly. Some migrate more than 4000 km from Southern Canada to Central Mexico. It now looks likely that the longest migration is by dragonflies who make a 14 000 - 18 000 km round trip from India to southern Africa stopping off at the Maldives and the Seychelles.
Longest adult life Lasius niger, ant queen survived 28.75 years in captivity.
Pogonomyrmex owyheei, ant queen, 30 estimated in the wild.
Longest life cycle Buprestis aurulenta larva, a wood boring beetle, emerged after 51 years
Shortest adult life Dolania americana (Ephemeroptera), a mayfly, lives for less than five minutes after her final molt. During the five minutes she chooses a mate, mates, and lays her eggs.
Shortest generation time Rhopalosiphum prunifolia, an aphid, has the shortest generation time of 4.7 days at 25o C.
Most polyandrous (female with highest number of mates) Apis dorsata (Hymenoptera:Apidae) a queen bee mated 53 times, each with a different male.
Chrysochus cobaltinus (Coleoptera: Chrysomelidae), a blue milkweed butterfly female, had up to 60 matings, though some of these were multiple matings with the same male.
Loudest Brevisana brevis (Homoptera: Cicadidae), a cicada, produces a calling song with a mean sound pressure level of 106.7 decibels at a distance of 50 cm.
Best "new" man Male Nicrophorus orbicollis, a burying beetle, participate in all activities, remain with the brood throughout development, and can take over all parenting responsibilities if the female disappears.
The above insect records, taken from Walker, T.J., ed. 2001. University of Florida Book of Insect Records, 2001.
Fastest muscles Termes panamensis, (a termite) has the fastest muscles in the world. It needed film shot at 40 000 frames per second to calculate the speed at which T. panamensis snaps its jaws shut, and the result is 70.4 m s-1. Its jaw muscles are so big that they fill half the space inside its head, and they are triggered by seeing an intruder's face inside the nest.
Longest sexual intercourse In many stick insect species males are never or hardly ever seen, however in other species the males can maintain intercourse for months at a time.

Flight data from some insects (from various sources)

Insect Speed metres per second Wing beats per second
Scorpion fly 0.5 28
Field grasshopper 0.5  
Mosquito 0.9  
Damselfly 1.5 16
Stag beetle 1.5  
Ammophila wasp 1.5  
House fly 2.0 190
Common wasp 2.5  
Large white butterfly 2.5 12
Honey bee 2.5 250
Monarch butterfly 2.8  
Bumblebee 3.0-4.5 130-240
Cockchafer 3.0 46
Hoverfly 3.5 120
Horse fly 4.0 96
Desert locust 4.4  
Hummingbird hawk moth 5.0 85
Hornet 6.0 100
Dragonfly 7.0 38
Fruit fly (Drosophila)   300
Midge (Scottish)   >1000
German wasp, Vespula germanica   250
Swallowtail butterfly   5

4 main functions of a sense of smell in insects, plus examples

Sexual attraction Gathering of male moths to a female releasing a pheromone
Recognition of nest mates Ants, bees and wasps recognise nest mates and intruders. Ants lay down trails between nest and food source.
Egg laying attractants Blowflies and carrion beetles are attracted to rotting meat as this provides a food source and habitat for larvae.
Food attractants Dung beetles attracted to the smell of dung as a food source and also as an egg laying site.
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