Insects our six legged friends

What Are Insects?

          Insecta is a class of invertebrates from the phylum Arthropoda and are probably the most commonly recognised of all invertebrates. Insects comprise 56% of all known species on the planet within 29 orders. Insects are described as having a chitinous exoskeleton made up of three body parts, the head, thorax and abdomen. Connected to the thorax they have three pairs of jointed legs and connected to the head they have two segmented antenna and two compound eyes. Having these parts is the only thing the orders have in come though.

The Orders of Insects:

Archaeognatha - Bristletails

Thysanura - Silverfish

Ephemeroptera - Mayflies

Odonata - Dragonflies and damselflies

Plecoptera - Stoneflies

Blattodea - Cockroaches

Isoptera - Termites

Mantodea - Mantids

Grylloblattodea - Rock crawlers or Ice crawlers

Dermaptera - Earwigs

Orthoptera - Crickets and Grasshoppers

Phasmatodea - Stick and Leaf insects

Embioptera - Web spinners

Zoraptera - Angel insects

Psocoptera - Barklice and Booklice 

Phthiraptera - Parasite Lice

Hemiptera - True Bugs

Thysanoptera - Thrips

Megaloptera - Alderflies and Dobsonflies

Raphidioptera - Snakeflies

Neuroptera - Lacewings and Antlions

Coleoptera - Beetles

Strepsiptera - Strepsipterans

Mecoptera - Scorpionflies

Siphonaptera - Fleas

Diptera - True or Two winged flies

Trichoptera - Caddisflies

Lepidoptera - Butteflies, skippers and moths

Hymenoptera - Bees, Wasps, Ants, Sawflies and Woodwasps

          The class Insecta has one of the most diverse body plans of the animal kingdom, with individuals being found in nearly every single habitat across the planet (The exception being the polar caps). Another thing that makes the insect class an interesting one is that individuals have been found to feed on nearly every available food source across the planet with Coleoptera have individuals of each of the different food sources present in their order.

Why are insects our friends?

          First off I'll start by saying that the study of these six legged marvels is known as entomology, which has been studied from prehistoric times by many cultures but wasn't until the 16th century that it had a more scientific focus. Second off, whilst many of the six legged organisms, Hexapod, are very useful to us, many more of them are considered pests and aren't our "friends".

          The ones that people would considered our "friends", are more appropriately consider useful to us and our wider environment. A lot of the Insecta class are considered useful due in the most to acting as the first animals on the trophic food chain, which means that most of the species in the world are dependent on insects existing as a direct food source or as a food source for their prey. However,  many insects have more commercial uses such as production of food, pharmaceuticals, forensic investigations and many other areas which we will discuss in a future post. Along with food and commercial gain they also help with the local environment by pollinating plants, clearing detritus and recycling waste material, and sometimes they even feed on insects and other invertebrates that can cause you and I harm.

          This was a very brief overview of what makes an insect an insect and why they are good for us, along with a list of the orders present within the class Insecta in the next few posts I plan to go more in depth into this fascinating class and why they are some of the most important species to humans. Hope you've enjoyed reading and hope to see you next time.
Heyze

Species of the week: Tegenaria spp.

Figure 1. Tegenaria domestica

Tegenaria Spp.

Domain: Eukarya

Kingdom: Animalia

Phylum: Arthropoda

Class: Arachnida

Order: Araneae

Family: Agelenidae

Genus: Tegenaria 

Species: domestica(Figure 1), atrica, gigantea, parietina and saeva. (This is a list of the UK tegenaria species and is also worth mentioning that not all of these are considered part of the Tegenaria genus but have in fact been moved to a new genus Eratigena).

          Of all the spiders in the UK nothing strikes as much fear in people scared of spiders as the Tegenaria spp. do. They are one of the largest species in the UK and are very common in the household as that is their preferred place of residence. The fear of this spider comes from it's menacing look, large size, its fast speed and the fact that it invades our private residences but despite this they are a relatively friendly species. The only species that they are associated with is T. agrestis, also known as the hobo spider (Figure 2), which in the US it is considered a dangerous species but on closer inspection it is more likely that bites from the hobo spider are actually caused by Loxosceles reclusa, also known as the brown recluse spider (Figure 3). Unlike Tegenaria spp. the brown recluse spider can have a potentially fatal bite. Although the bite has no fatal effects it has been reported that in very large specimens that when they have bitten (Which is rare) that it felt like a pinch with a very small amount of localised swelling.

Figure 2. The hobo spider Tegenaria
agrestis

Figure 3. The brown recluse spider
Loxosceles reclusa

Where to find them:

          As a lot of the people in the UK will know the Tegenaria spp. as the big hairy spider that tries to live in the house with them, this isn't an entirely accurate description of where they live though. Most of the species in the UK tend to live in less used buildings, such as sheds, where they can build a web that isn't going to be destroyed quickly. In the shed they are usually found in corners where there is a crevice that can take them out of view.

 Tegenaria domestica:
          This species is more reliant on peoples homes as it requires the heat for it to survive, especially across the winter period, but it can still be found in cave entrances and in hollow trees and produces the largest web of the five species. This is the most commonly found of the Tegenaria spp. in the UK and attains the smallest size of a body size of 10mm.

Tegenaria gigantea/duellica:
          This species is less reliant on peoples homes but can still be found in them, it tends to live more in out buildings, and in the outdoors in general. This species tends to be found in the southern half of Britain and attains a body size of 18mm.

Tegenaria saeva:
          Essentially this spider is the same as T. gigantea but instead of being found in the south it is found in the northern and western parts of Britain.

Tegenaria parietina:
          This is another species that tends to hang around outside. This species is the largest with a body size of 20mm and can be found across Britain. Because of its large size it is considered to be a nightmare spider by some.

Tegenaria atrica:
          This spider is the same as T. parientina only it is less common and tends to be slightly smaller with an average body size of 18mm.

Web type:

          Tegenaria spp. are a type of funnel web making spider (not to be confused with the Sydney funnel web spider) that makes a tubular web in small crevices and behind walls and furniture. The tubular web then flows into a sheet web that is generally in a triangular shape with a few loose strands trailing off at the end. The strands serve a warning that prey is approaching on the sheet web where the spider will then run up and inject it's prey to immobalise it before dragging it into its funnel to feed on.

Lifespan:

          The lifespans of the Tegensaria spp. are very similar with the male living till mating and after a couple of weeks dying off with the female usually using him as a food supply. The female is able to live for several years and can lay multiple egg sacs a year up until she dies.

Mating:

          Mating time occurs in the Autumn and is the reason you find so many of these spiders in the house during the Autumn. This is because the male goes out in search of a females web in order to mate with her. Once he has found the web he will proceed to find the female in her funnel where he will then produce a packet of sperm, in his pedipalps, to wipe on her epigyne, which is then stored in the sperm receptacle and can be used for the rest of the spiders life. After this exchange the male may then stay in the web with the female or it will wonder off but ultimately it will die after a couple of weeks.

Figure 4. The white egg sac pulled out from its dirt and debris
cover than can be seen in the top left.

          After mating the female will wait until April (Spring) to lay her eggs in an egg sac made of a special kind of silk. These egg sacs are quite interesting in that the female will use dirt and debris to cover the egg sac (Figure 4) so that predators don't recognise it as anything more than a ball of dirt. Online it says that the eggs will hatch around midway through April, from my personal experience though they will hatch from anywhere between 15 and 25 days. 

          After hatching the babies are free to leave the web and go start their own lives. It takes less than a year, and several moults, for them to reach an adult size but the males tend to not mate until there second Autumn.

Feeding:

          Mostly Tegenaria spp. will feed on anything that creeps into its web and triggers the outer trip strands. In a captive environment I have had great success on feeding them with crickets and locusts with the occasional meal worm, but I have these from keeping pet reptiles if you don't have access to captive live food then you can just as easily use other insects from the garden.

Captive care:

Figure 5. My Tegenaria spp. set up with my female Tegenaria
gigantea feeding in the front.

          These species are very easy to keep. I use a smallish plastic faunarium with some sort of cave to be used for a funnel web and a sheet web across the rest of the tank (Figure 5); I then provide twigs and dried leaves to give it a more natural feel to it. I feed the spider about once a week as more than that will make it fat and can reduce its life span. Water isn't necessary in the tank as the spider can get all of its hydration from the insects that it feeds off of. If the spider is young when you get it, or from a previous spiders egg sac, then it should be kept in a smaller environment as it may not be able to find its food, with the size being upgraded every couple of sheds. The food should also be around the same size as the spiders body as any bigger may cause damage to the spider.

I hope this article has helped or taught you something new.

Thanks for reading,

Heyze.

History of invertebrates: Part 1 Ediacaran epoch

The Ediacaran Epoch: Where the invertebrates around us today started

          The true origins of the early Metazoa (Another name for the Animalia kingdom) is still a mystery to us. What we do know now though is that by 600 million years ago (mya) marine invertebrate fauna had begun to make an appearance. This happened during the late Proterozoic Eon known as the Ediacaran Epoch which began at around 605 mya and lasted till around 570 - 540 mya. The Ediacaran fauna contains a lot of fossil records with the first evidence on the origins of modern phyla, however, we still do not know how these early records fit into the evolution of life. 

          The modern phyla that are represented in the Ediacaran fauna are Porifera, Cnidaria, Echiura, Mollusca, Onychophora, Echinodermata, a group of annelid-like organisms and quite possibly, Arthropods. However, a lot of the animals discovered from this time cannot be positively placed in categories with living taxa as they may be parts of phyla that were wiped out at the Proterozoic-Cambrian transition.

Figure 1. An artists impression of what the "Garden of Ediacara
would look like

Figure 2. A fossilised Dickinsonia showing its bilateral sym-
metry. The organism managed to reach a meter in length.

          The Ediacaran fossils have been found in more than 100 sites in the world with a large majority found at Ediacara in the Flinders Ranges of South Australia which is where the name is derived from. Most of these Edicaran organisms have been found to be shallow water species but they have also been found in deep water and continental slop communities. Most of the species found have been soft bodied organisms  with none have heavily shelled bodies. Many of these Edicaran organisms are described as being immobile discs, fronds, tubes, and quilted mattresses that stayed attached to the same place their entire life. The period of time when they existed is even known as the "Garden of Ediacara" because nearly all of the organisms filtered water for energy or used sunlight which meant that they did not attack each other.However, even though they were soft bodied, chitinous structures had developed to start forming the early jaw structures of annelid-like worms. Even with these structures though it is still hard to find Edicaran fossils because the soft bodied organisms do not fossilise well and many of the fossils are just imprints of the bodies found in sandstone beds and ashes. Many of the organisms found in the Ediacaran epoch lacked complex internal organ structures and their body plan followed radial symmetry, however, towards the end large animals with bilateral symmetry had started to appear and did have more complex internal organ structures (Such as the the segmented, sheet-like Dickinsonia seen in Figure 2).

          The Ediacaran epoch heralded the end of the Precambrian period and the Proterozoic eon. These periods were followed by the Cambrian period that is characterised by the great "explosion" of skeletonised life that evolved and brought about the fist mass extinction of most of the Ediacaran fauna. It is still a mystery though, as to why skeletonised animals appeared at this time and in such large quantities. Data on the Earths early atmosphere tells us that the atmosphere lacked oxygen that would be needed for animal life to evolve. This oxygen would have then been added to the atmosphere from the early Cyanobacteria (blue-green algae) that used photosynthesis to get the energy they needed. Some workers still just prefer the idea that early metazoan life was just soft bodied so isn't present in the fossil records due to them not fossilising properly. However, some metazoan meiofauna has been discovered in the Proterozoic strata in China which suggests that the organisms were tiny in the Ediacarna epoch and that by the Cambrian period they had just started to grow larger with the increase in atmospheric oxygen levels. This can also be debated though because large creatures did exist during the Ediacaran epoch such as the Dickinsonia. WHat we have seen though is that early chitinous jaws had started to form which would allow Precambrian organisms to start feeding on other animals and plants. We also know from modern studies that animals evoolve in an ecological arms race which means that the skeleton was the start of the ecological arms race that started as a defense against predators.

          The development of these skeletons did mark the end of the Proterozoic eon and marked the start of the Phonerozoic eon that started with the Cambrian period. The Cambrian period included most of the trophic levels of feeding that we see in our current marine communities, which included giant predatory arthropods, and was very different from the peaceful life of the Ediacaran epoch. This fascinating period is what we will be looking at in part 2 of this series.

Thanks for reading,
Heyze.

Where did the invertebrates come from: A brief overview

Where did it all begin?

          In the beginning all there was on earth were Prokaryotes, organisms that lack membrane enclosed organelles and a nucleus, and they don't have linear chromosomes. The Prokaryotes can be split into the two kingdoms Eubacteria, which include Cyanobacteria and Spirochetes, and the other Archaea (Archaebacteria). Everything else in the world now a days is classed under the Eukaryotes which is comprised of four kingdoms Fungi, Plantae, Protista and, Animalia. All of the invertebrates are part of the kingdom Animalia.

          The kingdom Animalia is defined as multicellular, ingestive, heterotrophic organisms, that is to say that the feed on other organisms and organic materials. All of the animal kingdom has a common ancestor that would have been a Prokaryote mean that you and I come from the same place as the invertebrates did.

           The earliest known record of life on Earth is somewhat of a debate. One record was found to be 3.8 billion years old however, they were trace records which could have also just been mineral deposits. The earliest known record that isn't contested is 2 billion years old but these also contain multicellular organisms which suggests that life must have evolved earlier than this date. Therefore at our current understanding the best estimates guess that life first appeared between 3.8 and 2.5 billion years ago.

           After life developed on the planet it began to evolve. At about 1.6 billion years ago plants and animals had their last common ancestor which means it took somewhere from 2.2 to 0.9 billion years for animals to first appear in the Earths oceans. Fossil records suggest that the earliest time for invertebrates to have existed was at least 600 million years ago (mya) with most extant species found today being found in the fossil record by 500 mya. It then took another 130 million years for any of the animal kingdom to walk on land and become a terrestrial species.

            So since the beginning it took the invertebrates 3.2 to 1.9 billion years to evolve from their prokaryote ancestors. Next time I'll start to go into more detail of where early life started and how the invertebrates came to rule the planet for a time.

A little bit about invertebrates

What is an invertebrate?

          Simply put an invertebrate is an animal that lacks a backbone. This is a very broad statement and includes around 95 percent of the entire animal kingdom and is made up of around 30 phyla (Phyla is the plural of the word phylum which describes a large group of organisms that are related to eachother. It is the next division after kingdom and before class.). 

What are the phyla?

          Here is a list of the phylums for invertebrates and the estimated number of describe species:

Porifera - 5500

Placozoa - 1

Monoblastozoa - 1

Rhombozoa - 70

Orthonectida - 20

Cnidaria - 10,000

Ctenophora - 100

Platyheminthes - 20,000

Nemertea - 900

Rotifera - 1,800

Gastrotricha - 450

Kinorhyncha - 150

Nemata/ Nematoda - 25,000

Nematophora - 320

Acanthcephala - 1,100

Entoprocta - 150

Gnathostomulida - 80

Priapula - 16

Loricifera - 10

Cycliophora - 1

Sipuncula - 320

Echiura - 135

Annelida - 16,500

Onychophora - 110

Tardigrada - 800

Arthropoda - 1,093,514 (This comes from a book published in 2003 so this has likely jumped to closer to 2,000,000)

Mollusca - 93,195

Phoronida - 20

Ectoprocta - 4,500

Brachiopoda - 335

Echinodermata - 7,00

Chaetognatha - 100

Hemichordata - 85

What does this tell us?

          From this list alone we can see that the largest invertebrate phyla is Arthropoda with close to 2,000,000 identified species. If we compare this to the phylum Chordata, (Everything that isn't an invertebrate) which has has approximately 50,00 describe individuals, we can see that just one one invertebrate phylum comprises most of the planets animals.

          The phylum Arthropoda has 13 classes in it which include spiders, scorpions, millipedes, centipedes, crustaceans and insects. So Arthropoda is what people colloquially refer to as bugs, micro beasts and insects.

I hope this has been a useful little look into the invertebrate world, and hope to see you next time.

Heyze.

Welcome

          Welcome all to my blog. I am a zoology graduate with a passion for invertebrates and I would like to share that passion with all of you so I have decided to start a blog about just that, so hopefully you guys will learn some new and interesting things about these wonderful animals and maybe some of you will even be inspired to go out and discover even more new things for your self.

          This blog is also a place for me to learn at the same time, because you can't ever know everything about invertebrates. So if I get anything wrong please don't hesitate to let me know by dropping me an email at captivecritters@googlemail.com. I will also try to answer any questions as well if you just send your questions to the email address above.

          A little more about me. I've been interested in invertebrates, and animals for that matter, since I was a little kid when I would run all around the garden catching as many species as I could and placing them in jam jars so that I could watch them and identify them. This then led to me to pursue them as a career so I took a course in zoology. Since graduating I am now looking to get a job in the conservation sector teaching school kids about invertebrates and their impact on the world.

          With that, welcome to Invertebrates in all their glory. I hope you find this and interesting and useful place to find information.

Thanks,
Heyze