Skip to main content

#38: Arachnids

Harvestman (aka daddy longlegs)

Mite

Spider

 

Litinsects #38: Arachnids

Today we are taking a little excursion outside the world of insects into a neighboring class of arthropods, the ARACHNIDS. Most people think spiders when they hear arachnids but the group includes so much more than that!
  • In addition to spiders 🕷, the arachnids consist of mites and ticks, scorpions 🦂, pseudoscorpions, tailless whip scorpions, and harvestmen (aka daddy longlegs which are NOT actually spiders!). The closest relatives of arachnids are horseshoe crabs
  • Like insects (and all other arthropods), arachnids have jointed appendages and a hard exoskeleton and grow by molting
  • Arachnids have neither wings nor antennae. They possess only simple and no compound eyes
  • Unlike insects, which have 3 body segments (head, thorax, and abdomen) arachnids generally have two body sections, the PROSOMA, aka head, and the OPISTHOSOMA, aka abdomen (but the two may be fused into one in some groups)
  • Arachnids are easily recognized by their 8 legs but they also possess two additional pairs of appendages towards their heads. CHELICERAE are basically jaws that can be used as pincers or modified into fangs to inject venom. PEDIPALPS are used either for feeding or locomotion and can be highly specialized in various groups. (In scorpions for example, the pedipalps are modified into huge pincers, making it seem like they actually have 10 legs).
  • This group has an almost worldwide distribution. The majority of species are terrestrial and predatory
  • Among the smallest arachnids are mites, some as tiny as 0.1mm! (More on my mite friends to come later!) On the other end of the spectrum sits the goliath bird eater, a spider that can measure up to 30cm
If there is one thing I want you all to take away from this post it is this: spiders are NOT insects and they are not the only arachnids!
Labels:

Comments

Post a Comment

Popular posts from this blog

#4: Simple Eyes

Litinsects #4: Simple Eyes Yesterday I talked about compound eyes, the multi-faceted structures that most insects use to see the world 👀 But insects actually have another visual system as well, composed of simple eyes or OCELLI. Unlike compound eyes, ocelli are composed of only one structure which makes them comparatively “simple” although they are still very important. These are light-detecting organs consisting of a single lens with sensory cells. They can detect movement but don’t form complex images. “Ocellus” comes from the Latin word oculus, meaning eye. So these structures are literally “little eyes” Ocelli are located on the insect’s head, usually between or adjacent to the compound eyes. They are usually dome-shaped, somewhat shiny structures In most flying insects (such as flies, dragonflies, bees, etc.) there tend to be three ocelli in a triangle arrangement (see photo). Some terrestrial insects (like cockroaches) have only two ocelli ...
Post a Comment
Read more

#33: Hamuli

A row of hamuli on the wing of a bee The top two hamuli shown here are hooked onto the back edge of the forewing. Litinsects #33: Hamuli Today’s post is another on anatomy and is about a structure found in a group of insects that probably everyone around the world is familiar with... The order HYMENOPTERA is comprised of bees, wasps, sawflies, and ants. (Yes, ants are actually related to bees and wasps.) At around 150,000 described species it is among the top 4 largest group of insects (along with beetles, flies, and butterflies). One defining characteristic of hymenopterans are HAMULI (see photos). Hamuli (singular hamulus) are microscopic hook-like structures on the front surface of the rear wing that hook into the back edge of the front wing. This system interlocks the two wing pairs during flight, allowing them to beat in unison and act as one functional pair of wings. Basically hymenopterans have developed an anatomical wing coupling feature to enhance flight efficiency. (In the t...
Post a Comment
Read more

#39: Leaf cutter ants

© Gail Sumway  Litinsects #39: Leaf cutter ants You’ve likely seen them in nature documentaries; countless individuals on a trail with abstract leaf cut-outs on their backs... these are LEAF CUTTER ANTS. They can carry impressively heavy loads on their backs, up to 20 times their body weight. But have you ever wondered what they do with all these leaves that they carry back to their nests? You might assume that they eat them but they don’t! What they actually do is way cooler than that. Leaf cutter ants participate in a MUTUALISTIC SYMBIOSIS with fungi, a close relationship that benefits all parties. Ants cultivate underground fungus gardens in their nests and it’s actually the fungi that eat the leaves as they decompose. The fungus in turn serves as food for the ant colony! Because the fungus needs the ants to stay alive, it is a mutually beneficial relationship. Ants actively groom the gardens by removing parasites and even secrete anti-microbial substances to prevent growth ...
Post a Comment
Read more