welcome to our last lecture covering phylum arthropoda in this lecture we'll be covering subphylum hexapoda and this is chapter 21 in your textbook hexapoda is an exceptionally diverse subphylum but all the members in this subphylum have six legs which is where they get their name from hexa six pota legs and all of their appendages are uniramus so this is not like what we saw in crustaceans because in crustaceans they had byramus appendages or they sometimes will have birmis and uranus appendages in hexapods all of their appendages are uniramus the hexapod body plan is composed of three tag mata the head the thorax and the abdomen all of the appendages will be present on either the head or the thorax segment there are no appendages present on the abdomen and this is because of a lack of the expression of the dll gene so we talked about dll or distillase gene when we went to the the first lecture on arthropods and we talked about how this gene plays a role in whether an appendage will be uteranus or byramus in the case of hexapods this gene is not expressed at all on their abdomen so they do not develop appendages in that region there are two classes of hexapods the first that we're going to talk about is the class entognatha and this includes springtails so if you've ever seen a springtail this is a picture of one here this guy's a springtail and there's also a picture of some black springtails on the last slide of this presentation they're not always black they can be different colors but they're very very very very small they almost unnoticeable that's how small they are and all of the members of this class are characterized by the fact that they have their mouth parts contained within their head capsule so when you look at a mouth part you have you know the hinges and then you have whatever the extension is so if it's a jaw you have the rest of the jaws if they're mandibles you have the you know the extension of the mandibles but in the case of antagonisms the vast majority of their mouth parts are not visible when you look at them because they're contained within the head so if we look at these as an example this is the mouth parts of the springtail and the only part of the mouth parts that you can really kind of see protruding from the mouth is this little region here it's kind of hard to see but also if you look at this diagram of a springtail down below this is the mouth region and only part that you can really see of the mouth parts that protrudes from the mouth is kind of this little segment here all the rest of the mouth parts are not visible if you just look at springtails or other antagonists because they're located within the head you would have to actually break open the head to see the rest of the mouth parts and then the other main class of hexapods are insecta and insecta include ants flies moths beetles bees flies all the things that you normally would think of as an insect belong to this class and one key characteristic of them is that they have ectognathus mouth parts so their mouth parts are located on the outside of their head and you can see that in this ant really well obviously these very clear mandibles you can see the hinges of the jaws and the entirety of the jaws outside of the head capsule same thing with this mosquito this mosquito mouth parts are all located outside of the head so they're very visible when you look at these animals and then there are two groups of insects we have our pterygotes which are our winged insects and then you have atera goats which are the wingless insects class and secta hold many titles for one they're the most diverse and abundant group of all arthropods so that's a lot of diversity but even more impressive than that there are more species of insects than all other species of animals on the planet combined so that's a lot of biodiversity and then on top of that there are more members of the class insecta than all other animals combined together so if you took every animal on the planet every animal that is living right now and put them all together and counter them up and then you counted all the insects on the planet right now there will be more insects by number than there are all other animals on the planet so that's insane that's a lot of insects and so when you look at the amount of diversity and the amount of numbers of insects it's no wonder that they've been so successful on this planet they're basically everywhere the only habitat that they haven't been able to successfully colonize is the oceans and we know that crustaceans have basically uh colonized that area when it comes to arthropods but pretty much everywhere else you can find insects and their nearly ubiquitous nature has been attributed to two main factors one their ability to fly and two their rapid ability to adapt so you can imagine if you can fly from place to place you can more easily colonize new habitats which is exactly what insects have been able to do but in addition to that your ability to rapidly adapt helps them to colonize these new habitats as well so you can fly to a new habitat but if you can't adapt to the conditions of that habitat then a species won't be able to proliferate there but insects have been very successful at traveling to new habitats and then adapting to those habitats very quickly and then reproducing relatively quickly to inhabit the habitat and when insects insects are able to occupy every niche of a habitat so one insect will occupy one niche and then another insect will travel to that new habitat as well occupy another niche and it just keeps going and going until basically every niche in that habitat is occupied by some species of insect insects can be pre-living or parasitic and they can be herbivorous carnivores or they can be saprophytic depending on the species and the conditions insects like all other arthropods have a cuticle and their cuticle is reinforced with these proteins called scleroproteins and they provide rigidity and strength to the exoskeleton while also allowing it to be lightweight and this is important for the mobility of the insect so they have to have that cuticle to keep them protected but if their cuticles too heavy then they can't move quickly or they can't fly or makes flight very difficult so having a lightweight yet strong and rigid cuticle helps them to survive in various conditions in addition to the cuticle being lightweight and protective it's also waterproof and this is really important for the insect's ability to become completely terrestrial no so not all arthropods have this you know watertight waterproof uh cuticle we talked about the crustaceans roly-polies in the last lecture and how they still have to live in moist and wet environments to prevent them from drying out because their cuticle doesn't really hold water well in the tissues insects don't have to worry about that they can inhabit places as dry as deserts because their cuticles really good at keeping the water maintained within their bodies so each segment of the insect body plan is covered by the cuticle and the cuticle is composed of kind of four main parts and each of those parts is referred to as a sclerite which is just a fancy word for a plate so there are four main plates in the cuticle there is the turgum or the nautum which is on the dorsal side and you've heard me say this word turgum before um i think i pronounced it wrong in the last lecture um but they also were present in the uh crustaceans on the segments that were not protected by the carapace right so it's a similar thing here and then they have the uh ventral side is covered by the sternum plate and then we have two pleura on this on the lateral sides so here and here and all of these plates are composed of that cuticle exoskeleton so they can protect the insect the head of the insect is where all of the mouth parts are located so of course you have your mandibles and your maxilla and your labial palps but you also have your antennas that are located on the head and they also will have these three oscillate commonly on the head so you can see them here you can kind of see them a little bit in the previous slide when you look at the ant's head you can kind of see the oscillate present there so that's pretty much the main components of the header for obviously eating and sensing their environment and then the second tag mata is the thorax and the thorax is composed of three main parts we have the prothorax which is the most anterior region which is in this picture of this grasshopper this region here and then we have our mesothorax which is posterior to that which would be this region here and then the most posterior portion of the thorax right before the abdomen is the metathorax which would be present here and each segment has a pair of legs so you can kind of see them here there's the pair of legs in the front for the prothorax and then the pair of legs here these ones are attached to the mesothorax and then these long legs for the cricket that are helping them to jump and to high heights and things like that are attached to the metathorax and also the wings will be attached to either the meso or the metathorax depending on the species but that's where they're um attached to and then the final segment of the insects is the abdomen and the abdomen is usually composed of between 9 and 11 different segments and um there sometimes will be cersei or ovipositor on the very last segment and then the genital pore will be generally between the eighth and ninth segment but this can vary depending on the insect insects can use a variety of methods to get from place to place they can walk run jump swim burrow fly you name it they can do it and they're able to use all these methods of locomotion because they have specialized appendages that allow them to move in different ways all of their appendages though are controlled by cross-striated muscles similar to the skeletal muscle that we see in humans and when an insect is walking they'll often use something called the tripod method and this is where of their six legs they'll have two the front and back legs on one side in contact with the ground and then the third uh or the middle leg on the opposite side in contact with the ground so it gives them this kind of tripod look to their legs when they're walking and this provides them with stability so you can imagine if they move all three legs on one side of their body and then all three legs on the other side of their body they would wibble and wobble right but using this tripod method allows them to be stable as they walk around their environment insects also have wings and most insects have two pairs of wings they have one pair of four wings and one pair of hind wings but there are some insects that only have one pair of wings and these belong to a group called diptera an example can be seen here are the true flies um only have one pair of wings and then you also have insects that lack wings altogether insects that don't have wings this could be due to a ancestral characteristic because they share common ancestor of all insects lack wings or can be a derived characteristic depending on the species and those insects that lack a second pair of wings but they do have one pair of wings they often will have something called halters at the back which are these kind of like nub-like extensions where the second pair of wings would have been and they use these halters for stabilization and and equilibrium as they're flying through the air and as i mentioned before the wings are attached to the exoskeleton at the meso and metathorax so in this image here you can see the four wing is attached at the mesothorax and the high wing is attached at the metathorax and where the wings are actually attached on the thoracic segment is at a space between the turgum and the pleura so when we were talking about the sclerites um in the last slide we mentioned that there is the oh let's choose a different color we have our tergum which is on the dorsal side then we have two pleura and then we have our sternum between the turgum and the pleura there's this kind of hinge space and this is where the wings are attached and this location plays a major role in their ability to fly which we'll talk about in the next upcoming slide wings are composed of cuticle they're actually just thin layers of cuticle and it's generally two membranes of cuticle that are stuck together and the cuticle will also have these veins in them and so you can see the veins very well in this picture of a fly like all these kind of darker veiny segments and these veins are just strengthened areas of cuticle that provide rigidity and strength for the insects so that their wings don't crumple under the pressure of wind or um they don't fold when they move flight and insects is facilitated by two muscle groups we have our direct muscles which are attached directly to the wing and we have indirect muscles which are attached to usually the cuticle or other parts of the body of the insect but they are not directly attached to the wing most insects will use their indirect muscles to flap their wings but there are some that use direct muscles for flapping but we won't really talk about that in this lecture so much of the insects that use indirect muscles to flap their wings they use their direct muscles to kind of position the wings so that they can get thrust and they can have more controlled movements as they fly so an example of this is seen in this cartoon of this flyer bee they're showing you that figure eight movement or path of the wings and that's facilitated by the direct muscles pulling the wing down in certain air currents and up in certain air currents so they can more accurately control their flight and they can fly the best way possible so how does this all work so we start with the sternotegral muscles which are shown here this muscle here and their name makes kind of sense they run from the sternum down here to the tergum up here right and so those indirect muscles will contract and when they contract it brings the tergum closer to the sternum so the distance between the turgum and the sternum will decrease and this pulling down of the turgum will cause the wings to lift and then while this is all happening the longitudinal muscles here in the center are relaxed so the sternosterno turbo muscles contract while the longitudinal muscles are relaxed and this causes the wings to go up now when the sternal turtle muscles relax and the it will cause the longitudinal muscles to contract so now these muscles here that run the length of the animal will contract and these muscles here will relax and when that happens that pushes the tergum out and bows it more and when it pushes the turgum out that causes the wings to go down so this is how this alteration of contraction and relaxation between the sternotergal indirect muscles and the longitudinal indirect muscles is how they can get that flapping motion there's a couple of types of neuronal contractions that stimulate the muscles to contract we can have synchronous contractions which means that one nerve impulse equals one wing stroke so for every nerve pulse you get one flat or you can have asynchronous neuronal control which means one nerve impulse will result in multiple wing flaps so you get one impulse and you might get several even up to hundreds of wing flaps with just that one impulse and this asynchronous wing pulse allows for them to have far more quick speed when it comes to flight and it's all facilitated by the fact that when the sternotegral muscles contract it causes the longitudinal muscles to be stretched and in response to those stern integral muscles becoming relaxed the longitudinal muscles not only just contract but they also will start to snap back so that initial snapping back and is not facilitated by any sort of nerve impulse it's just the fact that there was tension pulled on those muscles and then they naturally will spring back and so this basically they antagonistically work against each other to stimulate each other's expansion and contraction expansion and contraction and that's how you get multiple wing pulses for one nerve impulse the mouth parts of insects are morphologically diverse but they're all ectopicus so they all lie outside of the head capsule and insects can be herbivores carnivores scavengers or parasites depending on the species and conditions and even within the parasites we have some variation there are some insects that are hyper parasites so they're parasites of parasites and then we have some that are parasitoid and parasitoid insects oftentimes will lay their eggs within a particular host and those eggs will develop into larva and then the larvae once they are ready um to leave the host will oftentimes kill the host and um some examples of both parasitoid and hyper parasitic insects are included in the last slide of this presentation there are a couple of videos that you can feel free to watch to get more information on these lifestyles and feeding structures so the feeding structures and the habitats of intex are heavily specialized for them to take advantage of their food source and so we can see that here in this this graph is a couple examples the proboscis of a butterfly is specialized for them to obtain nectar whereas the mouth parts of a grasshopper are clearly very very different and that's because grasshoppers don't uh drink nectar they eat leaves right so their mouth parts are specialized for that the fascicle of a mosquito looks something like this with a sharp edge to it like a hypodermic syringe and they're specialized for obtaining blood from mammalian or avian hosts right so they're different structures for different functions and this is beneficial because it allows for these insects to optimize their ability to obtain food however it does limit their diet so a butterfly cannot use as proboscis to eat leaves or to suck the blood from a host it can only use their proboscis to get nectar from flowers right so their diet is heavily limited based on whatever their mouth parts are and this is beneficial for insects overall because it limits the competition between different species a butterfly and a mosquito are not going to be in direct competition with one another because they do not have the same food source so this is has some benefits and some drawbacks to having such specialized mouth parts the gut of an insect is complete so it comes with a four gut midgut and hindgut the four gut is the most anterior region and includes the crop um and the esophagus in the mouth which is all kind of this region here and then we have our mid gut which lies posterior to that and the mid gut is responsible for absorption of nutrients primarily and then finally we have the the hindgut which is everything that's posterior to the mid-gut and its primary function is the reabsorption of ions and water insects have an open circulatory system they use their dorsal heart and aorta to pump hemolymph to the various tissues throughout the body the primary purpose of the hemolymph is to distribute nutrients to all the tissues and cells it's not to distribute oxygen and so what they use instead to undergo respiration is a tracheal system and so we talked about trachea in the first um arthropod lecture as they pertain to arachnids and the trachea and arachnids and insects work in very similar ways so if you need a refresher on how the trachea work i recommend going back to that presentation and taking a look at that section of the lecture but um the trachea even though they perform similar functions and work in similar ways in arachnids and insects they are analogous in these two groups so they did not arrive arise from a shared common ancestor instead trachea evolved independently in both groups and the use of a tracheal system is actually more efficient than using their circulatory system and so that's why it's been maintained it allows for more efficient and more direct gas exchange than if they used cells within their hemolymph to carry oxygen to the tissues so the tracheal system is primarily composed of trachea obviously and the trachea open up to the environment via the spiracles or sphericals depending on how you pronounce it and um you can see them there you see them here as well and these are openings in the exoskeleton that open up to the environment and the sphericals have a valve within them that closes when the organism is not inhaling or exhaling and this allows for them to minimize water loss which is really really important for a terrestrial lifestyle and so if you want to see a video of this there's a video at the end of this presentation that shows you i think it's a prank mantis or a stick insect um but you can see their trachea up close you can see that valve opening and closing to help minimize the water loss in the insect and then the trachea are supported by these structures called tinidia and the tinidia are shown here in this picture as like a spring but basically all it is is hardened strengthens uh thicker segments of cuticle within the trachea and they hold the trachea open and so it prevents them from collapsing altogether these are important because if the trachea collapsed then the organism would suffocate right they couldn't undergo respiration so those tinidia hold the structure open and they also play a role in bringing in oxygen which we'll talk about in a few seconds and the trachea branch to every part of the body so you can see that in this picture up here they're showing you all that purple in this image showing you that the trachea and tracheoles are able to access all the tissues and pretty much every cell within the body there's no cell within the insect body that's more than a couple of millimeters away from a trachea or tracheal and so i've already mentioned this term tracheals but tracheals are these thinner vessels that look just like this or similar to this um that kind of branch off from the trachea so the trachea are constantly branching and branching and as they're branching they're getting thinner and thinner until they become these very thin fluid-filled vessels that are in direct contact with the cells and tissues and this is where gas exchange actually occurs so the trachea the tracheals will be in direct contact with the cells and they will deliver oxygen to the cells that need it and then they will uptake the co2 um as the waste product and then the co2 will travel from the tracheals to the trachea and then out of the sphericals into the environment so the uh larger insects are able to like almost like breathe if you will so that video at the end of the presentation that i talked about where you can see the sphericals you can also see this kind of breathing motion and so what insects will do is they'll use a combination of their muscles and their tinia to inhale and exhale so they use their muscles um to basically uh exhale so they will contract their muscles and that will contract or put pressure on the trachea which will expel the gas that's contained within them out into the environment and then when those muscle fibers relax the tinio will spring back because they are for providing that structure right so they've been compressed they'll spring back and that will cause uh inhale so it'll bring in the gases and so this antagonistic uh interaction between the tanedia and the muscles allow the insect to inhale and exhale inhale and exhale there's a really good uh video of that at the end of this presentation to see how that works and then um even aquatic insects have trachea but instead of using their tinia and muscles to inhale and exhale they just allow for diffusion directly into the trachea small insects will do this as well so they don't have to use their muscles or anything to bring in oxygen instead they're so small or they're in the water so the oxygen will just directly diffuse into the trachea through the tracheals to the cells and co2 will just diffuse straight out insects use mouth piggy and tubules to undergo osmoregulation but also for the removal of nitrogenous waste and we talked about my piggy and tubules before in the first arthropod lecture when we talked about arachnids but the my pigeon tubules and arachnids and insects are analogous to one another even though they're analogous they do function in in similar ways so if you need a refresher on how myopic and tubules work i recommend going back to that lecture and reviewing that portion of the presentation to get a refresher my picking tubules and insects are located between the mid gut and hindgut you can see them here is all this kind of yellowy fibers between the mid-gut and the hindgut are the malpiggian tubules in this lower picture here they also have them present here um as kind of green spaghetti looking material in this cartoon between the mid-gut and the hindgut the primary nitrogenous waste product of insects is uric acid so we're going to spend some time talking about how uric acid gets into the mouth piggy and tubules and how it gets removed from the body so when we're looking at the malpigian tubules there is a difference in ph in that tubule on the very ends of the tubule the ph is more alkaline so in this area the ph is um higher right so um we'll say ph is alkaline and this is important because under normal physiological ph uric acid is not soluble so this is the only part of the tubule where uric acid or urate can be brought into the tubule because it can be dissolved so the uh uric acid potassium salts all different types of salts are brought into the malpigian tubule and in this case potassium and urate are brought in together and in your book they uh use the notion of khur to show you potassium and urate so they're brought into the malpudian tubule when this occurs it causes water to passively diffuse into the tubule as well and then as the potassium and urate are traveling down the mount pigeon tubule co2 will also be brought into the tubule when co2 is brought in the co2 will bind with potassium to make potassium bicarbonate which is this here when the potassium bicarbonate is is produced it will cause the ph of the fluid in the in the tubule to decrease so now it's more acidic sorry for the poor handwriting but it's more acidic now so with the fluid being more acidic uric acid will no longer be uh soluble it will be precipitate and so now it's a precipitate solid in the tubules and it will remain solid until it leaves the body so from here the uric acid will then go into the hindgut it travel down the hindgut excess water from the filtrate will be reabsorbed excess ions will be reabsorbed and then the uric acid as a solid will be released from the body a few species of insects are parthenogenic but the vast majority are dioecious and dioecious insects undergo internal fertilization internal fertilization can occur via one of two mechanisms one you have the direct transfer of sperm from the male into the female reproductive tract which we're probably most familiar with and then two you can have the use of a spermatophore and a spermatophore is just this packet of sperm that the male insect will deposit onto a substrate for the female to later come along and collect the sperm an example can be seen here with this grasshopper that little white bubble of sperm will be deposited either on that flower or nearby leaf or stem and then the female will later come by and collect the sperm from that packet the use of a spermatophore is actually an ancestral characteristic so all of the ancestors share common ancestors of all insects use the spermatophore for reproductive purposes and whether there's the use of a spermatophore or direct injection of sperm in both cases the sperm is stored in the seminal receptacle of the female until she's ready to undergo fertilization and the seminal receptacle is here oops that's here in the female and so the sperm will be stored there for later use once a a insect gives birth they can either be viviparous so they give birth to live young or they can be over paris which means they lay eggs and some examples of some eggs can be seen here all those little uh brown balls on the edge of this leaf are each an egg that will give rise to some sort of insect and there are a couple of different growth and development characteristics that we can see or patterns that we see in insects we have insects that are considered to be a metabolism so that means they do not undergo metamorphosis and then we have insects that are metabolism which means they do undergo stages of metamorphosis during their development in both cases whether they are a metabolism or metabolism the insects will undergo several rounds of molting the stages between the mulch are called in stars and in in insects that undergo metabo endigo metamorphosis these instars may show different morphology but in those that are a metabolism they will look the same as the adults the smaller version so the stages of a metabolism insects include the egg juvenile and adult so if we were to look at um an example here of the silverfish silverfish hatch from their egg so let's say we draw a stage of an egg here so the juvenile silverfish will hatch from their egg or they'll be birthed live and then they're just basically small immature versions of the adult and as they undergo several rounds of malt they just get bigger and bigger there aren't really any major changes that occur in this insect as they undergo growth and then eventually they'll just reach their adult size and they'll be sexually mature and they're ready to go so there's not much change between the young the young version and the adult in a metabolism insects and then those that undergo metamorphosis we have two main groups those are hemi metabolisms and those are holo metabolis and we'll spend a lot more time on the next slide talking about the differences between them but you can see some differences here looking at um a hemi metabolism example using this roach and in a whole metabolism example using this larva but we'll take a more close look at that next hemi metabolism metamorphosis is often referred to as incomplete metamorphosis this is because the changes between the youth and the adult stage are far more gradual than what we see in complete metamorphosis which is what we'll talk about next and the major life stages in the incomplete metamorphic life cycle include the egg nymphs and the adult stage and what you might notice here is that from this picture is that the nymph kind of sort of resembles the adult but there are some key characteristics that are missing for one the biggest thing that you might notice is the difference is the presence of wings the nymphs does not have wings where the adult does and so what happens is actually when the nymph arises from the egg they'll have these small buds and as the nymph undergoes uh periods of molting with each molt those buds will become wings and then the wings will grow in size until we get to the adult stage where they will have fully developed wings um and they'll be ready to undergo reproduction because there's a lot of other changes that occur between the nymph and the um adult stage and so this differs from a metabolism insects because a metabolism insects are basically just small sexually immature versions of the adult they don't undergo very many changes except for a growth in size whereas in hemi metabolism or incomplete metamorphosis these insects do develop more characteristics that are indicative of the adult that they did not have in their nymph form and some examples of insects that undergo incomplete metamorphosis include grasshoppers mantids and dragonflies then we also have complete metamorphosis or holo metabolism metamorphosis and this is the process that most insects undergo that undergo metamorphosis and the major life stages include the egg the larva the pupa and the adult and each of the life stages has a primary responsibility so the larva's main responsibility is to eat and grow so all they do is eat grow mold eat grow molds they just do that over and over and over again until they are ready to undergo the next life stage which is the pupa and the pupa's main responsibility is differentiation so um the caterpillar will then transform into the butterfly in this kind of intermediate pupa stage and then the adult's main responsibility is to undergo reproduction and this responsibility is so important that in some insect species they actually don't even have mouth parts like they're not you have feeding structures in their adult they are are strictly supposed to go out mate lay eggs and die so not all species are like that of course but there are some species that are so dedicated to having their adults reproduce that they don't even eat and having this type of life cycle is beneficial because it allows for the larva and the adults not to have competition with one another so the larva occupies a completely separate niche than the adult does and that way you know the the larvae aren't eating up all the resources from the adult and adults aren't eating all the resources from the larva this allows for them to grow as much as possible and have as many members as possible because they're not competing with one another and the transition from the juveniles into the adults in both the nymph stages and in the egg larva pupa stages are dictated by the concentrations of the hormone juvenile hormone which you've probably read about in the group assignment insects have several methods they can use to protect themselves from both physical and environmental threats one way that insects can protect themselves from environmental threats is through the process of diapause and diapause is a period of dormancy to prepare the insect for unfavorable conditions and generally this occurs between the fall and the spring so a insect will begin the process of diopause sometime in late fall and then they will remain dormant or kind of like hibernating through the winter and then they will emerge generally in the spring the process of diopause is internally controlled but it's triggered by environmental cues so changes in humidity daylight and temperature and other factors like that will cause the insect to start undergoing the process to to go into diapause and during this time there's an arrest of growth so a lot of times the pupa stage will occur during this time because there is no growth in the pupa right there's just differentiation and then in the case of like a pupa going and developing into a butterfly the butterfly will emerge in the spring it's not just in in these in this cases there are a lot of different species of insects that will maybe burrow into the ground and they do not undergo any growth during the winter and then they will emerge in the spring and they'll then start to eat again and grow again so it's just a period of pause diapause right a period of pause where they're basically just waiting out those unfavorable conditions until things become favorable again and then to protect themselves from physical threats there's a couple of other methods they can use of course they have their exoskeleton that is really good at protecting them from predators and falls and dehydration and things like that so this rhino beetle always is a really good example of a very hard sturdy exoskeleton to protect um the insect from the environment but any type of cuticle exoskeleton is also protective and then they some of them produce chemical defenses so they will either produce poor smells or bad tastes poisons or irritants to deter predators some use mimicry this is a good example this insect here looks very much so like a leaf and this is a way for them to protect themselves from predators right if this insect looks and moves like a leaf then a predator is less likely to come and attack it and eat it and they can also use this as a deterrent so in the case of this image here this is a monarch butterfly and um butterflies are toxic birds that eat these will have serious issues but there are some butterflies that will mimic the look of a monarch butterfly so that predators think oh my gosh i shouldn't eat that it's going to make me sick when in actuality they're completely harmless they're not poisonous at all so mimicry is a really can be a really effective way of protecting yourselves from predators and then they can also fight back right so a good example that if you've ever been stung by a bee you know what this is a stinger is one way that bees and other insects will fight back as well as horns and spikes and quills there are various different ways that an organism can fight and then of course they can run away they can fly away they can run they can hop they can jump and swim away from predators the relationship between humans and insects is more complicated than you might think this is because insects are ecologically economically and medicinally important for both positive and negative reasons now on the whole we as humans benefit more and the whole planet benefits more from insects than we are harmed by them but there are some benefits and drawbacks so some major benefits that we get from insects is number one they're pollinators and so all of the crops that we have to eat that we feed to our livestock and that we use for fuel and for products are pollinated by insects and so without them all the crops that we need to survive and get products from would surely die um we also get commercial products directly from insects like beeswax honey and silk are just a few examples of products that we get directly from insects that we use in our everyday life insects are also a natural way of pest control there are many carnivorous insects that eat other insects that would be pests for us an example that i like are the praying mantises that take up shop on our deck those praying mantises i like having them there because i know that they're eating the pests that i don't want to make it into my home because of the woods behind our house right so they can be a natural way of keeping the pest level down without having to use chemicals and then also probably the most one of the most important uh benefits that we get is biodiversity so insects are a kind of base fundamental level of the food web in many habitats they are a source of food for many uh insects amphibians um reptiles mammals birds you name it there's probably a predator that eats that insect and so they without insects we wouldn't see the biodiversity that we see in many habitats and then also insects are major decomposers so when a tree falls or there's leaf litter or an animal dies then some of the first animals to come and try to take care of that situation aren't insects and without them we would be swimming in debris and and dead animals right so they they benefit us in a lot of different ways but there are some drawbacks so some insects if left unchecked can completely decimate crops and other foliage this can happen of course when we have commercial crops but it can also occur in forests and things like that in in nature where particular insects particularly invasives are really bad at this will go through and just completely decimate areas and can even cause certain plants to go extinct and then one thing that we all hate uh insects for the most is that they can be vectors for disease so this guy obviously is pretty famous there's mosquito and mosquitoes are notorious for being vectors of disease but there are also other arthropods out there and insects out there that are vectors for human disease and so that's one major reason why we don't like pests pest insects and then finally which is a little bit less of an issue because it's more annoying than anything but it can be a serious problem is that insects can be pests to humans so they can destroy your property like in the case of termites and moths right termites can eat the wood that is present in the walls of your home and that can destroy your property moths come in and can eat the wool in your sweaters and destroy your property that way there are a lot of different ways that insects can cause you serious issues but even if they're not causing destruction to property they can cause psychological problems right so if you find that your house gets infected with some sort of infested with some sort of insect like ants or roaches or bed bugs that can cause you psychological issues as you're constantly worried are they gonna eat on me are they gonna get in my food what's gonna happen right so there's a lot of drawbacks that come with insects but when you put it all together the pros and the cons there are a lot more pros to insects than there are the cons to insects okay with that said you've made it to the end of the arthropod lectures you can go ahead and start reading chapter 21 read the intro 21.1 through 21.4 and then i've also included some videos here as well um that might help you to understand some of these concepts the sphericals up close that's that video so you can see the opening and closing of the valve as well as kind of the inhaling and exhaling of insects a video on metamorphosis another video to show you um how the flight muscles work so if you didn't quite understand what i was saying that video has a good animation to show you how the indirect muscles coordinate to allow an insect to fly also the videos on the parasitoid and hyperparasit hyperparasitic insects and then finally the last video is really not that helpful but it's really kind of cool on the first slide i had a picture of a caterpillar that almost like is made of glass or crystal and those are called jewel caterpillars and so i just put a video here of jewel caterpillars just in case you're interested okay excellent the next lecture that we'll have we'll begin our lectures on deuterostomes and we're going to be talking about echinoderms