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

#13: Insect Legs

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...
Post a Comment
Read more

#22: Caterpillars

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...
Post a Comment
Read more