Arachnid Digestive System & Diet

Instructor: Julie Zundel

Julie has taught high school Zoology, Biology, Physical Science and Chem Tech. She has a Bachelor of Science in Biology and a Master of Education.

You've seen ticks on your dog, or spiders busily building a web. But how much do you know about how arachnids digest their food? This lesson will explore the arachnid digestive system as well as their diet.

Arachnids Defined

Let me introduce you to the Portia spider, which hunts and kills other spiders. This clever arachnid will climb into another spider's web, wait for it to come over, and then kill it and eat it.

Or the Hackled Orb spider, which doesn't have venom to immobilize its prey, so, instead, it wraps it in a cocoon so tightly it is crushed.

Or the countless species of tick that inject their host with a neurotoxin, thus numbing the area so the unsuspecting prey has no idea its skin has been penetrated and its blood is now flowing into the tick's belly.

A tick feasting on a human
tick bite

Other than feasting on the flesh and blood of others, what do these three have in common? They are all arachnids, which are animals that belong to the Arachnid class and include mites, ticks, spiders, daddy-long legs and scorpions. There are around 70,000 species of arachnid, with over half of those being spiders.

You know what the Portia spider, the Hackled Orb spider and what some ticks eat, but what about other arachnids?

Arachnid Diet

Arachnids have different diets, depending upon the group and species. Scorpions and spiders eat mostly insects or other arachnids, but are known to eat animals like lizards, mammals, birds and amphibians.

A scorpion eating a millipede
Scorpion eating millipede

Ticks and some mites are parasites, meaning they live on another creature, taking that host's nutrients. While most are carnivores, some arachnids eat plants and fungi too. For example, some species of mite suck the juices from plants or eat fungi. And there's a species of jumping spider living in Central America that gets 90% of its nutrients from plants.

Arachnid Digestive System

So how do arachnids digest all of this food? I'm glad you asked! Let's see how their digestive system, or the bodily system responsible for breaking down food, works.

Many arachnids produce venom that paralyzes their prey. While it's still paralyzed, the arachnid will inject digestive juices into the animal, which turns the animal's insides into a mass of goo (oftentimes while it's still alive). Then the arachnid sucks up the animal's insides (kind of like drinking a milkshake... well, if the milkshake were made of liquefied animal guts). Yummy!

Other arachnids use their chelicerae and pedipalps to crush the prey and then use enzymes to break the tissues down further. Both the chelicerae and pedipalps are appendages on arachnids that can be claw or pincher like.

Other arachnids, like ticks, have evolved mouthparts that allow for skin piercing and subsequent blood sucking.

You might be wondering why arachnids don't just chew their food like you and me. Arachnids, as it turns out, do not have a mouth like us, so they cannot bite and chew in the same way. For these reasons they must break down the animal before they can consume it.

Let's follow some food through the arachnid's digestive system so you can get an idea about how the whole thing works. Check out the image to see where each structure is on the arachnid (note: we won't cover every structure, only those associated with digestion).

The arachnid internal anatomy. We will focus only on the digestive system.
spider anatomy

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