Spiders do not have antennae like insects. Instead, they use other senses and features of their body to detect the same things that antennae sense for insects.
Insects have antennae to detect smells, distinguish hot from cold, feel the surface of an object, listen to sounds, and detect movements around them. Spiders, on the other hand, use other parts of their body to perform the same functions that antennae do for insects – most notably, the hairs that are built on their bodies.
What Does a Spider’s Body Look Like?
Spiders only have two main parts of their body: the cephalothorax, which is the head and the torso of the spider, and their abdomen.
On their cephalothorax, spiders have:
- Eight legs (four on each side)
- Pedipalps (or feelers) at the top of their body
- Chelicerae (or mouthparts)
- Hairs on legs and body (also called urticating hairs)
The structure of a spider’s body is designed in such a way that they’re able to move around quickly and also be able to hide from their prey at the same time to ambush them. They have eight mechanical legs which will help the spider move equally as fast in all directions, but also jump if necessary.
A big difference between insects and spiders is also the structure of a spider’s head and the features it has around its mouth. For example, spiders have chelicerae, which carry fangs. These fangs are then used for spiders to catch their animals of prey and to administer the venom, which then kills or paralyzes the target.
But perhaps one of the most important body parts of spiders are the hairs on their body, which play several important functions.
The Crucial Role of Hairs for Spiders
One of the main distinguishing features between insects and spiders is that spiders don’t have antennae, but they use hairs on their body, which are also called the trichobothria, or urticating hairs, to perform similar tasks as an antenna would.
A spider has approximately 2400 hairs on each of its legs, and some spiders also have hairs on their bodies. These tactile hairs give them a significant advantage over their prey, as they help spiders spot nearby animals and help spiders recognize any animals that are flying by the spider.
These hairs are primarily used for moving around different surfaces with ease, as they provide the spider control over each surface and the ability to navigate easily, as it helps them stick to the surface easily.
Spiders also have poor eyesight and their hearing is also not the best, so they have to rely on their hairs and the sense organs they have in their cuticles.
A spider’s hairs also help the spider to:
- Sense the animals that are flying near the spider
- Help the spider hear better
- Mate and sense the mating counterpart as it is ready to mate (hairs on pedipalps)
- Taste foods (which is especially true for hairs around their mouths)
- Sense vibrations going on around the spider
- Capture their prey
Spider hairs play some crucial roles in the survival of the spider. Without the hairs, a spider would not be able to function properly, detect its surroundings, move around its habitat, capture its prey, and perform other critical functions that are needed for them to survive.
In many cases, these spider hairs replace antennae that are found on insect bodies, which is why spiders don’t have them.
Why Do Insects Have Antennae?
To help you better understand why spiders don’t need an antenna, let’s take a look at some of the most important functions that the antenna plays for the insect.
Insects use their antenna to:
- Feel the surface of an object
- Sense cold and hot
- Detect movements of air and wind
- Recognize the environment around them
Antennae are crucial for the survival of an insect. They help regulate the flight path of the animal as they fly around the environment. They also help them sense the world around the insect, as the antenna helps the insect sense smells, feel surfaces of an object, distinguish hot from cold, and more.
Perhaps even more importantly, these antennas allow the animal to detect other animals around them, which is essential for their survival. For example, it enables them to defend themselves against their predators. Not only that, but they’ll also help them catch and locate potential animals of prey thanks to their sensory features.
These antennae can be detected in animals like ants, flies, centipedes, crustaceans, bees, wasps, and other similar creatures. On the other hand, spiders are chelicerates, which means they use their chelicerae and hairs to perform roughly the same functions as the hairs do for insects.
Why Do Spiders Not Have an Antenna?
Spiders don’t have an antenna because they’re chelicerates, meaning that they’ll depend on their chelicerae and the hairs on their body to detect the movements around them.
Instead of having an antenna on their body, spiders have chelicerae and hairs, as well as other crucial body parts to help them perform the same functions as an antenna would for the insect.
Also, an antenna would hinder a spider’s movement because it would make them unable to crawl into thin surfaces such as crevices that they prefer to hide in. They want to be as tight and as space-efficient as possible when they move around, as they don’t want to arouse a lot of attention when moving around.
To conclude, spiders don’t have antennae. They’re chelicerates, so they focus on the functions that are provided to them by their chelicerae and their hairs.
The main mechanism that replaces the antenna is the hair system. With it, the spider detects movement around them, sense threats and opportunities, as well as make sure they are able to move around as efficiently as possible without making themselves heard or seen.