Litinsects

Litinsects #22: Caterpillars Since you are freshly familiar with metamorphosis from my last posts, I will today be talking about caterpillars 🐛 and some structures that change drastically in appearance from before to after metamorphosis: legs. Caterpillars are the worm-shaped larval stage of butterflies and moths. They have huge appetites; they mainly feed to grow and gain energy for their transformation into adulthood. In order to do this they need to get around, for which they use le gs because only adult stages have wings.  But insects only 3 pairs of legs, right? So where do all these extra legs come from all down the sides of their bodies?  Caterpillars have 3 pairs of TRUE LEGS, attached to their thorax, which are jointed and have little claws on the end. These legs are still present after metamorphosis, though they will have changed substantially Additionally, they usually have 2 to 5 pairs of PROLEGS, which are protrusions fr...

Litinsects #21: Complete vs. Incomplete Metamorphosis Welcome to METAMORPHOSIS PART 3: Let’s start with a recap of my last two posts... Within winged insects (or PTERYGOTES), there are two different developmental strategies: HOLOMETABOLOUS insects undergo complete metamorphosis with 4 stages: egg, larva, pupa, and adult. All stages look completely different from one another HEMIMETABOLOUS insects undergo incomplete metamorphosis with 3 stages: eggs, nymph, and adult. The nymphal stages physically resemble the adults Nymphs of hemimetabolous insects typically share the same food and habitat as adults and exhibit similar behaviors whereas holometabolous insects usually look different, display different behaviors, and occupy different habitats in each life stage. The takeaway here is that holometabolous insects are very good at compartmentalizing certain tasks into different life stages, in order to reduce or eliminate competition among life stages! Th...

(© Brandon Thorpe) (© Brandon Thorpe) Litinsects #20: Hemimetabola Welcome to METAMORPHOSIS PART 2: Yesterday I discussed complete metamorphosis, where an individual’s appearance changes pretty drastically through its life stages. But some insects undergo a different kind of transformation: INCOMPLETE METAMORPHOSIS. These insects are HEMIMETABOLOUS (hemi = half/part, metabola = change) because they go through gradual changes to their body layout. This includes 3 life stages: egg, nymph, and adult. 1) As usual it starts with an EGG 2) A NYMPH emerges, which generally resembles the adult form of the insect but WITHOUT WINGS. Nymphs molt several times, growing in the process, but never enter a pupal stage. These nymphal stages are called INSTARS 3) The ADULT insect emerges after the final molt, with WINGS and REPRODUCTIVE ORGANS. Nymphs may differ from adults in coloration or body proportions but hemimetabolous insects usually have similar diets in ...

Litinsects #19: Metamorphosis, Part 1: Holometabola Who would like to join me on this 3-part adventure of insect metamorphosis? It is my hope that by the end, you will be TRANSFORMED... into a person who knows a lot more about insect metamorphosis than when you started! 😁 So here goes METAMORPHOSIS PART 1: Everyone knows that a caterpillar 🐛 makes a cocoon and emerges as a butterfly 🦋 , right? This is an example of COMPLETE METAMORPHOSIS (as opposed to incomplete which I will go over tomorrow). Butterflies, and a whole lot of other insects, are HOLOMETABOLOUS (holo = whole/entire, metabola = change), so called because the insect undergoes drastic changes in body layout and function and each stage is completely different in appearance from the others. This includes 4 life stages: egg, larva, pupa, and adult. 1) All insect lives begin with an EGG. Most hatch within a few days after being laid 2) From the egg emerges a LARVA. Some have legs, some do...

Litinsects #18: Spiracles and Tracheae Take a breath in... and out. Have you ever wondered how insects breathe? They don’t have lungs like we do. In fact they use a completely different respiratory system than vertebrates. Insects breathe through SPIRACLES, which are small holes in the exoskeleton along the thorax and abdomen. A tiny “door” to the spiracle can be opened and closed to reduce water loss Connected to the spiracles is a network of TRACHEAL TUBES that extend throughout the body. Gas exchange occurs by DIFFUSION across the walls of the smallest tubes. In insects, the respiratory system is SEPARATE from the cardiovascular system. Their “blood” does not carry oxygen to cells (technically they don’t have blood but a future post will go into that more) Some insects have collapsible internal sacs to store air for when their spiracles are closed. Aquatic insects use these air reserves while under water and can regulate buoyancy with the a...

Litinsects #17: Thrips Today I’m talking about a lesser known group of insects called thrips, which most people probably haven’t seen before because they are quite tiny. I worked with thrips for my master’s thesis so I was able to learn a lot about them and get these great photos. Here go some fun facts... Thrips are small insects (around 1mm) with very narrow and fringed wings that make up the order THYSANOPTERA (Greek thysanos =fringe, pteron = wing). FYI, thrips is both the singular AND the plural form Their mouthparts are ASYMMETRICAL, a feature that is unique to the group. The right side is reduced (vestigial) or absent and only the left side is used to scrape open plant cells and extract contents These insects feed on a wide variety of plants and are often considered PESTS of commercial crops. They are also vectors for plant diseases Thrips go through incomplete metamorphosis (which I will explain in a post coming up). They lay their eggs into p...

Litinsects #16: Cricket Ears Towards the beginning of this series, I posted about how grasshoppers hear using a TYMPANAL ORGAN, which is located on each side of their abdomen. Crickets, as well as grasshoppers, belong to the order ORTHOPTERA 🦗 (ortho = straight, ptera = wing) and also hear using tympana. Theirs, however, are located somewhere completely different and rather strange: their legs. Cricket tympana are located on the TIBIA of their forelegs Crickets call... and in order to find each other, they must obviously be able to tell where a call is coming from. Underneath the tympanum there is a network of pathways through which sounds can travel through the body and between the left and right tympana. The animals can gauge the DIRECTIONALITY of a sound depending on how sound waves act on both the external AND the internal surfaces of their tympana! This difference of pressure is vital for localizing the calls of fellow crickets. Crickets call...

Litinsects #15: The Success of Insects The first insects evolved around 410 million years ago. They have witnessed many global changes and numerous catastrophes that wiped out plenty of other species yet somehow they survived and continue to thrive. With around 1 million named species, insects currently account for around 2/3 of animals worldwide and are found in almost every kind of ecosystem. So what makes insects so successful? Here‘s what it comes down to: 1) An insect’s EXOSKELETON provides protection, support, and prevents desiccation (water loss) 2) Their SMALL SIZE means they can hide easily from predators, they require fewer resources to survive, and they can disperse easily (by themselves or by being carried) 3) FAST GENERATION TIMES means that insects potentially evolve faster due to the accumulation of more mutations per unit of time. This means, insects have many more chances for new species to arise than say an animal that needs years or decades ...

From: Nesbit, C. and Nesbit A. (2017) Insecta. teNeues Media GmbH, Kempen. Page 79  Litinsects #14: Earwigs Did you ever hear that earwigs will crawl into your ear while you sleep and lay their eggs in your brain? I know I did as a kid. Rest easy, that’s a total old wives’ tale! Let me shed some light on these misunderstood insects Earwigs make up the order DERMAPTERA, which means... anyone? You guessed it, “skin wings”. The forewings are short and leathery, modified into TEGMINA (similar in function to beetle elytra). The hindwings are very thin and fan-like and, although they are capable of flying, they very rarely do Those big pincers on their abdomen are actually modified CERCI, which are paired structures that are usually used as sensory organs. In earwigs, the cerci are modified into forceps-like PINCERS, which can be used either to hold prey, to grasp each other while mating, or for defense In some earwig species, mothers care for their eggs and hatched ...

Litinsects #13: Insect Legs Insect legs can be as diverse as the animals themselves. Some are long and slender like a crane fly’s, some are short and hefty like a mole cricket’s. But what all insects share is the number and layout of those legs. Hexapods have 6 LEGS, a pair each of fore, mid, and hind legs that are made up of the same basic units. Starting closest to the body, they are:  (1) the coxa, which attaches the leg to the thorax  (2) the trochanter (3) the femur, which is oft en the thickest segment  (4) the tibia, often covered in tiny hairs (5) the tarsus, which contains 5 “pseudo-segments”  (6) the pretarsal claws, of which most insects have 2 on each leg The basic units of the leg always occur in this order but may be reduced or highly modified in some species to fit certain tasks such as running, digging, swimming, grasping, or jumping. This photo sums it up perfectly: from < https://wiki.bugwood.org/File:Insect...