This question is one I get asked a lot. And it really depends on your definition of bugs.
Are spiders bugs? People tend to use the word bug loosely for any very small creature with legs. Are spiders small creatures? Yes they are. Do they have legs? They do. So by that definition, spiders are bugs.
If by bugs you refer to insects, then spiders are not bugs because they are not insects. Spiders are arthropods, invertebrate animals that have an exoskeleton, a segmented body, and paired jointed appendages.
Dictionary.com says that only a particular Order of insects, the Hemiptera, are the “true bugs.” They also say that “you are not wrong to call various insects bugs; because of the common usage of this meaning, it is certainly acceptable.”
Are Spiders Invertebrates?
Another question that keeps popping up on the forums, Quora, and Reddit.
Are spiders invertebrates? Yes, spiders are invertebrates. They do not have a backbone which is a defining feature of vertebrates.
Invertebrates are animals without a backbone or bony skeleton. This is by far the largest group in the animal kingdom: 97 percent of all animals are invertebrates. They range in size from microscopic mites and almost invisible flies to giant squid with soccer-ball-size eyes.
Take our Which Spider Is This? Quiz
The word “invertebrate” comes from the Latin vertebra, which means a joint in general, and sometimes specifically a joint from the spinal column of a vertebrate. The prefix in- means “not” or “without”.
Spiders are found on every continent except for Antarctica, and have become established in nearly every habitat with the exceptions of air and sea. There are at least 48,200 spider species, and 120 families have been recorded by scientists.
Only one species was described as herbivorous in 2008, and all other known species are predators, mostly preying on insects and on other spiders, although a few large species also take birds and lizards. It is estimated that the world’s 25 million tons of spiders kill 400–800 million tons of prey per year. How amazing is that!
They are also pretty crafty at catching prey. They trap it in sticky webs, lasso it with sticky bolas, mimic the prey to avoid detection, or run it down. You’ve seen a spider before, you know what I’m talking about.
While the venom of a few species is dangerous to humans, like the black widow, scientists are now researching the use of spider venom in medicine and as non-polluting pesticides. Also, spider silk provides a combination of lightness, strength and elasticity that is superior to that of synthetic materials.
We already mentioned that 97 percent of all animals are invertebrates. They include animals as diverse as sea stars and urchins, earthworms, sponges, jellyfish, lobsters, crabs, insects, spiders, snails, clams, and squids.
Invertebrates serve as
By far the largest number of described invertebrate species are insects.
Invertebrates can be classified into several main categories (some are debatable, but still used as terms of convenience):
- Sponges (Porifera)
- Comb jellies (Ctenophora)
- Hydras, jellyfishes, sea anemones, and corals (Cnidaria)
- Starfishes, sea urchins, sea cucumbers (Echinodermata)
- Flatworms (Platyhelminthes)
- Round or threadworms (Nematoda)
- Earthworms and leeches (Annelida)
- Insects, arachnids, crustaceans, and myriapods (Arthropoda)
- Chitons, snails, bivalves, squids, and octopuses (Mollusca)
Vertebrates include such groups as:
- jawless fishes
- jawed vertebrates, which include the cartilaginous fishes (sharks, rays, and ratfish)
- tetrapods, which include amphibians, reptiles, birds and mammals
- bony fishes
There are currently about 69,963 species described. They range in size from the frog species as little as 7.7 mm (0.30 in), to the blue whale, at up to 33 m (108 ft). Vertebrates make up less than five percent of all described animal species as we already know.
There is an exception to vertebrates, in that they traditionally include the hagfish, which do not have proper vertebrae due to their loss in evolution, though their closest living relatives, the lampreys, do. Hagfish do, however, possess a cranium.
How many eyes does a spider have? People usually think of spiders having eight eyes, but that’s not always true. Most spiders have eight eyes, but some species have six, four, two, or even no eyes. Even within a single species, the number of eyes may vary, but it’s always an even number. Why do they have so many eyes? With the main eyes being used for basic vision, the secondary sets of eyes are believed to be used to detect motion. This will aid them in response to a predator attack or the movement of their prey.
Are spiders insects? No they are not. Spiders are Arachnids and have two body parts: the cephalothorax (head + thorax) with eight legs, and the abdomen while insects have three body parts: the head, the thorax with wings and six legs, and the abdomen.
Are spiders mammals? Even though some spiders nurse their young with milk, spiders are not mammals, they are air-breathing, eight-legged arthropods. Mammals are vertebrate animals constituting the class Mammalia and characterized by the presence of mammary glands which in females (and sometimes males) produce milk for nursing their young.
Are centipedes insects? Centipedes are not insects even though they are small creatures that have many legs. They actually belong to myriapods, an arthropod group that also includes millipedes and other multi-legged creatures while insects are hexapods.