Aquatic Insects: Fill & Download for Free

Insofar as anyone knows, no cephalopod has ever evolved the ability to tolerate fresh water. We don’t have a scientifically accepted answer. Here’s what we do know.What are cephalopods?These are squids, octopuses, nautilus, and ammonites. Some of these animals have the largest, most sophisticated brains of any invertebrates. And the giant squid and the colossal squid are the largest known invertebrate species.[1]What about their relatives?Cephalopods belong to the phylum mollusca. This chart shows the relationships between mollusk classes[2] though scientists haven’t reached a consensus on the layout of this tree.[3]Only two classes of mollusks evolved the ability to live in freshwater: gastropods (snails) and the bivalves (freshwater mussels and clams). Insofar as anyone knows, the other classes never evolved freshwater species.Is it hard to adapt to fresh water?It’s complicated to do so but it has happened lots of times.One possibility is that it’s so hard to adapt to fresh water that only a few species made that change. To live in seawater, an animal must continually pump salts out and water into its cells. To live in freshwater, an animal must do the reverse. So, for an animal to move into fresh water from salt water, it must reverse existing cellular machinery.The machinery by which freshwater mussels maintain the correct salt and water balance is certainly complicated, as you can see in this chart depicting the main controllers in a single cell.[4]But it can’t have been all that hard since bivalves moved into freshwater habitats on at least 11 separate occasions and mollusks overall evolved the ability to live in fresh water about 40 times.[5] [6] Crustaceans, insects, and fish have also independently evolved this ability.[7]What about diet, physiology, or ecology?Maybe cephalopods never moved into fresh water because there wasn’t enough to eat in rivers. Octopus and squid are probably too big for many rivers and streams but some cuttlefish are small enough to survive in a river. They eat other mollusks, crabs, shrimp, and fish. In a freshwater environment, they would be limited to fish and there might not be enough fish in a typical river for them to survive or maybe fish would outcompete for that prey.Or maybe the way cuttlefish swim makes it difficult for them to navigate in rapidly flowing rivers. They rely heavily on a form of jet propulsion which uses more energy than the method fish use.[8]ConclusionsWe don’t know why there are no fresh water cephalopods. The majority of mollusk classes never evolved the ability to live in fresh water. So, cephalopods aren’t unusual.This hasn’t prevented some cephalopods from leaving the ocean. This octopus has figured out how to travel on land.[9]And occasionally, an octopus can even find something to eat on the land.[10]Footnotes[1] 500 million years of cephalopod fossils[2] The mollusca[3] Platydoris scabra | Tahsha Say[4] Toxicological perspective on the osmoregulation and ionoregulation physiology of major ions by freshwater animals: Teleost fish, crustacea, aquatic insects, and Mollusca - Griffith - 2017 - Environmental Toxicology and Chemistry - Wiley Online Library[5] https://www.biorxiv.org/content/biorxiv/early/2018/12/23/505305.full.pdf[6] https://repository.si.edu/bitstream/handle/10088/7390/IZ_Strong_et_al_FW_Gastropods_2008.pdf[7] Toxicological perspective on the osmoregulation and ionoregulation physiology of major ions by freshwater animals: Teleost fish, crustacea, aquatic insects, and Mollusca - Griffith - 2017 - Environmental Toxicology and Chemistry - Wiley Online Library[8] Aerobic respiratory costs of swimming in the negatively buoyant brief squid Lolliguncula brevis[9] Beware the Land-Walking Octopus | BBC America[10] Octopus Attacks Crab on Land

Good question—better than I took it for at first.They don’t breathe anything like land vertebrates do. Air enters the ant’s body through a row of tiny pores called spiracles along the flanks of the body like those on the caterpillar below. These lead to tubes (tracheae and tracheoles) that branch out among their body cells and deliver air directly to all the tissues throughout the body, rather than oxygen being delivered by the circulatory system. Most of the gas exchange in the smallest branches of this system is by diffusion rather than bulk flow of air.My first impulse was to say that insects can’t voluntarily control this, but a fact check showed I was wrong. They do have valves at the openings of the spiracles and muscles that can open or close them. Here’s a scanning electron micrograph of a spiracle of a cricket.Both photos are from Respiratory system of insects - Wikipedia, which says:Insects have spiracles on their exoskeletons to allow air to enter the trachea. In insects, the tracheal tubes primarily deliver oxygen directly into the insects' tissues. The spiracles can be opened and closed in an efficient manner to reduce water loss. This is done by contracting closer muscles surrounding the spiracle. In order to open, the muscle relaxes. The closer muscle is controlled by the central nervous system but can also react to localized chemical stimuli. Several aquatic insects have similar or alternative closing methods to prevent water from entering the trachea. Spiracles may also be surrounded by hairs to minimize bulk air movement around the opening, and thus minimize water loss.(emphases added by me)This doesn’t directly answer your question as to how long an ant can holds its breath, but at least it does show that it’s possible.

Why exactly, nobody can tell you yet. For some, it may be because of their navigation system, with them confusing artificial lights for the moon, but not all insects use the moon for navigation (e.g. moths don’t).What we can say is that UV light is far more attractive than LED light. Insect zappers work by emitting UV light (through a fluorescent bulb, a black light, or a mercury lamp), which all insects can see and so are naturally attracted to. Every insect is attracted to different spectra of light. For examples, moths are into UV and blue light, while mosquitoes and midges are also attracted to the green range of the spectrum. Kissing bugs, on the other hand, only go for the blue range. Of course, brightness and colour saturation also play a role.The reason is simply because of what the organisms’ eyes are attuned to. The best example I can think of is that of secondary aquatic insects, those with aquatic larvae and terrestrial adults, like dragonflies and mayflies. They find water by looking out for the horizontal polarisation of light reflected by water. Problem is that light reflected off asphalt, dark cars, and black sheets at night is also horizontally-polarised, and the insects will land on them and try to swim. If you go to a street lamp that shines a spot on a road, you will see this very clearly during an aquatic insect dispersal night: they will stay within the lit circle; as soon as they get to the edge, they will move back to the center.If a moth sees a huge UV glow, it will go towards it because that looks like a landmark or something that might be interesting. Not a very fancy explanation, but it fits, I think. The precise reason will differ for each insect group (e.g. only the secondary aquatics are attracted to horizontally polarised light).